Razor Pages with EF Core in ASP.NET Core - Update Related Data - 7 of 8

By Tom Dykstra, and Rick Anderson

The Contoso University web app demonstrates how to create Razor Pages web apps using EF Core and Visual Studio. For information about the tutorial series, see the first tutorial.

If you run into problems you can't solve, download the completed app and compare that code to what you created by following the tutorial.

This tutorial shows how to update related data. The following illustrations show some of the completed pages.

Course Edit page Instructor Edit page

Update the Course Create and Edit pages

The scaffolded code for the Course Create and Edit pages has a Department drop-down list that shows Department ID (an integer). The drop-down should show the Department name, so both of these pages need a list of department names. To provide that list, use a base class for the Create and Edit pages.

Create a base class for Course Create and Edit

Create a Pages/Courses/DepartmentNamePageModel.cs file with the following code:

using ContosoUniversity.Data;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.EntityFrameworkCore;
using System.Linq;

namespace ContosoUniversity.Pages.Courses
{
    public class DepartmentNamePageModel : PageModel
    {
        public SelectList DepartmentNameSL { get; set; }

        public void PopulateDepartmentsDropDownList(SchoolContext _context,
            object selectedDepartment = null)
        {
            var departmentsQuery = from d in _context.Departments
                                   orderby d.Name // Sort by name.
                                   select d;

            DepartmentNameSL = new SelectList(departmentsQuery.AsNoTracking(),
                        "DepartmentID", "Name", selectedDepartment);
        }
    }
}

The preceding code creates a SelectList to contain the list of department names. If selectedDepartment is specified, that department is selected in the SelectList.

The Create and Edit page model classes will derive from DepartmentNamePageModel.

Update the Course Create page model

A Course is assigned to a Department. The base class for the Create and Edit pages provides a SelectList for selecting the department. The drop-down list that uses the SelectList sets the Course.DepartmentID foreign key (FK) property. EF Core uses the Course.DepartmentID FK to load the Department navigation property.

Create course

Update Pages/Courses/Create.cshtml.cs with the following code:

using ContosoUniversity.Models;
using Microsoft.AspNetCore.Mvc;
using System.Threading.Tasks;

namespace ContosoUniversity.Pages.Courses
{
    public class CreateModel : DepartmentNamePageModel
    {
        private readonly ContosoUniversity.Data.SchoolContext _context;

        public CreateModel(ContosoUniversity.Data.SchoolContext context)
        {
            _context = context;
        }

        public IActionResult OnGet()
        {
            PopulateDepartmentsDropDownList(_context);
            return Page();
        }

        [BindProperty]
        public Course Course { get; set; }

        public async Task<IActionResult> OnPostAsync()
        {
            var emptyCourse = new Course();

            if (await TryUpdateModelAsync<Course>(
                 emptyCourse,
                 "course",   // Prefix for form value.
                 s => s.CourseID, s => s.DepartmentID, s => s.Title, s => s.Credits))
            {
                _context.Courses.Add(emptyCourse);
                await _context.SaveChangesAsync();
                return RedirectToPage("./Index");
            }

            // Select DepartmentID if TryUpdateModelAsync fails.
            PopulateDepartmentsDropDownList(_context, emptyCourse.DepartmentID);
            return Page();
        }
      }
}

The preceding code:

  • Derives from DepartmentNamePageModel.
  • Uses TryUpdateModelAsync to prevent overposting.
  • Removes ViewData["DepartmentID"]. DepartmentNameSL from the base class is a strongly typed model and will be used by the Razor page. Strongly typed models are preferred over weakly typed. For more information, see Weakly typed data (ViewData and ViewBag).

Update the Course Create Razor page

Update Pages/Courses/Create.cshtml with the following code:

@page
@model ContosoUniversity.Pages.Courses.CreateModel
@{
    ViewData["Title"] = "Create Course";
}
<h2>Create</h2>
<h4>Course</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form method="post">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <div class="form-group">
                <label asp-for="Course.CourseID" class="control-label"></label>
                <input asp-for="Course.CourseID" class="form-control" />
                <span asp-validation-for="Course.CourseID" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Course.Title" class="control-label"></label>
                <input asp-for="Course.Title" class="form-control" />
                <span asp-validation-for="Course.Title" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Course.Credits" class="control-label"></label>
                <input asp-for="Course.Credits" class="form-control" />
                <span asp-validation-for="Course.Credits" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Course.Department" class="control-label"></label>
                <select asp-for="Course.DepartmentID" class="form-control"
                        asp-items="@Model.DepartmentNameSL">
                    <option value="">-- Select Department --</option>
                </select>
                <span asp-validation-for="Course.DepartmentID" class="text-danger" />
            </div>
            <div class="form-group">
                <input type="submit" value="Create" class="btn btn-primary" />
            </div>
        </form>
    </div>
</div>
<div>
    <a asp-page="Index">Back to List</a>
</div>
@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

The preceding code makes the following changes:

  • Changes the caption from DepartmentID to Department.
  • Replaces "ViewBag.DepartmentID" with DepartmentNameSL (from the base class).
  • Adds the "Select Department" option. This change renders "Select Department" in the drop-down when no department has been selected yet, rather than the first department.
  • Adds a validation message when the department isn't selected.

The Razor Page uses the Select Tag Helper:

<div class="form-group">
    <label asp-for="Course.Department" class="control-label"></label>
    <select asp-for="Course.DepartmentID" class="form-control"
            asp-items="@Model.DepartmentNameSL">
        <option value="">-- Select Department --</option>
    </select>
    <span asp-validation-for="Course.DepartmentID" class="text-danger" />
</div>

Test the Create page. The Create page displays the department name rather than the department ID.

Update the Course Edit page model

Update Pages/Courses/Edit.cshtml.cs with the following code:

using ContosoUniversity.Models;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using System.Threading.Tasks;

namespace ContosoUniversity.Pages.Courses
{
    public class EditModel : DepartmentNamePageModel
    {
        private readonly ContosoUniversity.Data.SchoolContext _context;

        public EditModel(ContosoUniversity.Data.SchoolContext context)
        {
            _context = context;
        }

        [BindProperty]
        public Course Course { get; set; }

        public async Task<IActionResult> OnGetAsync(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            Course = await _context.Courses
                .Include(c => c.Department).FirstOrDefaultAsync(m => m.CourseID == id);

            if (Course == null)
            {
                return NotFound();
            }

            // Select current DepartmentID.
            PopulateDepartmentsDropDownList(_context, Course.DepartmentID);
            return Page();
        }

        public async Task<IActionResult> OnPostAsync(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            var courseToUpdate = await _context.Courses.FindAsync(id);

            if (courseToUpdate == null)
            {
                return NotFound();
            }

            if (await TryUpdateModelAsync<Course>(
                 courseToUpdate,
                 "course",   // Prefix for form value.
                   c => c.Credits, c => c.DepartmentID, c => c.Title))
            {
                await _context.SaveChangesAsync();
                return RedirectToPage("./Index");
            }

            // Select DepartmentID if TryUpdateModelAsync fails.
            PopulateDepartmentsDropDownList(_context, courseToUpdate.DepartmentID);
            return Page();
        }       
    }
}

The changes are similar to those made in the Create page model. In the preceding code, PopulateDepartmentsDropDownList passes in the department ID, which selects that department in the drop-down list.

Update the Course Edit Razor page

Update Pages/Courses/Edit.cshtml with the following code:

@page
@model ContosoUniversity.Pages.Courses.EditModel

@{
    ViewData["Title"] = "Edit";
}

<h2>Edit</h2>

<h4>Course</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form method="post">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <input type="hidden" asp-for="Course.CourseID" />
            <div class="form-group">
                <label asp-for="Course.CourseID" class="control-label"></label>
                <div>@Html.DisplayFor(model => model.Course.CourseID)</div>
            </div>
            <div class="form-group">
                <label asp-for="Course.Title" class="control-label"></label>
                <input asp-for="Course.Title" class="form-control" />
                <span asp-validation-for="Course.Title" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Course.Credits" class="control-label"></label>
                <input asp-for="Course.Credits" class="form-control" />
                <span asp-validation-for="Course.Credits" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Course.Department" class="control-label"></label>
                <select asp-for="Course.DepartmentID" class="form-control" 
                        asp-items="@Model.DepartmentNameSL"></select>
                <span asp-validation-for="Course.DepartmentID" class="text-danger"></span>
            </div>
            <div class="form-group">
                <input type="submit" value="Save" class="btn btn-primary" />
            </div>
        </form>
    </div>
</div>

<div>
    <a asp-page="./Index">Back to List</a>
</div>

@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

The preceding code makes the following changes:

  • Displays the course ID. Generally the Primary Key (PK) of an entity isn't displayed. PKs are usually meaningless to users. In this case, the PK is the course number.
  • Changes the caption for the Department drop-down from DepartmentID to Department.
  • Replaces "ViewBag.DepartmentID" with DepartmentNameSL (from the base class).

The page contains a hidden field (<input type="hidden">) for the course number. Adding a <label> tag helper with asp-for="Course.CourseID" doesn't eliminate the need for the hidden field. <input type="hidden"> is required for the course number to be included in the posted data when the user clicks Save.

Update the Course Details and Delete pages

AsNoTracking can improve performance when tracking isn't required.

Update the Course page models

Update Pages/Courses/Delete.cshtml.cs with the following code to add AsNoTracking:

using ContosoUniversity.Models;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.EntityFrameworkCore;
using System.Threading.Tasks;

namespace ContosoUniversity.Pages.Courses
{
    public class DeleteModel : PageModel
    {
        private readonly ContosoUniversity.Data.SchoolContext _context;

        public DeleteModel(ContosoUniversity.Data.SchoolContext context)
        {
            _context = context;
        }

        [BindProperty]
        public Course Course { get; set; }

        public async Task<IActionResult> OnGetAsync(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            Course = await _context.Courses
                .AsNoTracking()
                .Include(c => c.Department)
                .FirstOrDefaultAsync(m => m.CourseID == id);

            if (Course == null)
            {
                return NotFound();
            }
            return Page();
        }

        public async Task<IActionResult> OnPostAsync(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            Course = await _context.Courses.FindAsync(id);

            if (Course != null)
            {
                _context.Courses.Remove(Course);
                await _context.SaveChangesAsync();
            }

            return RedirectToPage("./Index");
        }
    }
}

Make the same change in the Pages/Courses/Details.cshtml.cs file:

using ContosoUniversity.Models;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.EntityFrameworkCore;
using System.Threading.Tasks;

namespace ContosoUniversity.Pages.Courses
{
    public class DetailsModel : PageModel
    {
        private readonly ContosoUniversity.Data.SchoolContext _context;

        public DetailsModel(ContosoUniversity.Data.SchoolContext context)
        {
            _context = context;
        }

        public Course Course { get; set; }

        public async Task<IActionResult> OnGetAsync(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            Course = await _context.Courses
                 .AsNoTracking()
                 .Include(c => c.Department)
                 .FirstOrDefaultAsync(m => m.CourseID == id);

            if (Course == null)
            {
                return NotFound();
            }
            return Page();
        }
    }
}

Update the Course Razor pages

Update Pages/Courses/Delete.cshtml with the following code:

@page
@model ContosoUniversity.Pages.Courses.DeleteModel

@{
    ViewData["Title"] = "Delete";
}

<h2>Delete</h2>

<h3>Are you sure you want to delete this?</h3>
<div>
    <h4>Course</h4>
    <hr />
    <dl class="row">
        <dt class="col-sm-2">
            @Html.DisplayNameFor(model => model.Course.CourseID)
        </dt>
        <dd class="col-sm-10">
            @Html.DisplayFor(model => model.Course.CourseID)
        </dd>
        <dt class="col-sm-2">
            @Html.DisplayNameFor(model => model.Course.Title)
        </dt>
        <dd class="col-sm-10">
            @Html.DisplayFor(model => model.Course.Title)
        </dd>
        <dt class="col-sm-2">
            @Html.DisplayNameFor(model => model.Course.Credits)
        </dt>
        <dd class="col-sm-10">
            @Html.DisplayFor(model => model.Course.Credits)
        </dd>
        <dt class="col-sm-2">
            @Html.DisplayNameFor(model => model.Course.Department)
        </dt>
        <dd class="col-sm-10">
            @Html.DisplayFor(model => model.Course.Department.Name)
        </dd>
    </dl>
    
    <form method="post">
        <input type="hidden" asp-for="Course.CourseID" />
        <input type="submit" value="Delete" class="btn btn-danger" /> |
        <a asp-page="./Index">Back to List</a>
    </form>
</div>

Make the same changes to the Details page.

@page
@model ContosoUniversity.Pages.Courses.DetailsModel

@{
    ViewData["Title"] = "Details";
}

<h2>Details</h2>

<div>
    <h4>Course</h4>
    <hr />
    <dl class="row">
        <dt class="col-sm-2">
            @Html.DisplayNameFor(model => model.Course.CourseID)
        </dt>
        <dd class="col-sm-10">
            @Html.DisplayFor(model => model.Course.CourseID)
        </dd>
        <dt class="col-sm-2">
            @Html.DisplayNameFor(model => model.Course.Title)
        </dt>
        <dd class="col-sm-10">
            @Html.DisplayFor(model => model.Course.Title)
        </dd>
        <dt class="col-sm-2">
            @Html.DisplayNameFor(model => model.Course.Credits)
        </dt>
        <dd class="col-sm-10">
            @Html.DisplayFor(model => model.Course.Credits)
        </dd>
        <dt class="col-sm-2">
            @Html.DisplayNameFor(model => model.Course.Department)
        </dt>
        <dd class="col-sm-10">
            @Html.DisplayFor(model => model.Course.Department.Name)
        </dd>
    </dl>
</div>
<div>
    <a asp-page="./Edit" asp-route-id="@Model.Course.CourseID">Edit</a> |
    <a asp-page="./Index">Back to List</a>
</div>

Test the Course pages

Test the create, edit, details, and delete pages.

Update the instructor Create and Edit pages

Instructors may teach any number of courses. The following image shows the instructor Edit page with an array of course checkboxes.

Instructor Edit page with courses

The checkboxes enable changes to courses an instructor is assigned to. A checkbox is displayed for every course in the database. Courses that the instructor is assigned to are selected. The user can select or clear checkboxes to change course assignments. If the number of courses were much greater, a different UI might work better. But the method of managing a many-to-many relationship shown here wouldn't change. To create or delete relationships, you manipulate a join entity.

Create a class for assigned courses data

Create SchoolViewModels/AssignedCourseData.cs with the following code:

namespace ContosoUniversity.Models.SchoolViewModels
{
    public class AssignedCourseData
    {
        public int CourseID { get; set; }
        public string Title { get; set; }
        public bool Assigned { get; set; }
    }
}

The AssignedCourseData class contains data to create the check boxes for courses assigned to an instructor.

Create an Instructor page model base class

Create the Pages/Instructors/InstructorCoursesPageModel.cs base class:

using ContosoUniversity.Data;
using ContosoUniversity.Models;
using ContosoUniversity.Models.SchoolViewModels;
using Microsoft.AspNetCore.Mvc.RazorPages;
using System.Collections.Generic;
using System.Linq;

namespace ContosoUniversity.Pages.Instructors
{
    public class InstructorCoursesPageModel : PageModel
    {

        public List<AssignedCourseData> AssignedCourseDataList;

        public void PopulateAssignedCourseData(SchoolContext context, 
                                               Instructor instructor)
        {
            var allCourses = context.Courses;
            var instructorCourses = new HashSet<int>(
                instructor.CourseAssignments.Select(c => c.CourseID));
            AssignedCourseDataList = new List<AssignedCourseData>();
            foreach (var course in allCourses)
            {
                AssignedCourseDataList.Add(new AssignedCourseData
                {
                    CourseID = course.CourseID,
                    Title = course.Title,
                    Assigned = instructorCourses.Contains(course.CourseID)
                });
            }
        }

        public void UpdateInstructorCourses(SchoolContext context, 
            string[] selectedCourses, Instructor instructorToUpdate)
        {
            if (selectedCourses == null)
            {
                instructorToUpdate.CourseAssignments = new List<CourseAssignment>();
                return;
            }

            var selectedCoursesHS = new HashSet<string>(selectedCourses);
            var instructorCourses = new HashSet<int>
                (instructorToUpdate.CourseAssignments.Select(c => c.Course.CourseID));
            foreach (var course in context.Courses)
            {
                if (selectedCoursesHS.Contains(course.CourseID.ToString()))
                {
                    if (!instructorCourses.Contains(course.CourseID))
                    {
                        instructorToUpdate.CourseAssignments.Add(
                            new CourseAssignment
                            {
                                InstructorID = instructorToUpdate.ID,
                                CourseID = course.CourseID
                            });
                    }
                }
                else
                {
                    if (instructorCourses.Contains(course.CourseID))
                    {
                        CourseAssignment courseToRemove
                            = instructorToUpdate
                                .CourseAssignments
                                .SingleOrDefault(i => i.CourseID == course.CourseID);
                        context.Remove(courseToRemove);
                    }
                }
            }
        }
    }
}

The InstructorCoursesPageModel is the base class you will use for the Edit and Create page models. PopulateAssignedCourseData reads all Course entities to populate AssignedCourseDataList. For each course, the code sets the CourseID, title, and whether or not the instructor is assigned to the course. A HashSet is used for efficient lookups.

Since the Razor page doesn't have a collection of Course entities, the model binder can't automatically update the CourseAssignments navigation property. Instead of using the model binder to update the CourseAssignments navigation property, you do that in the new UpdateInstructorCourses method. Therefore you need to exclude the CourseAssignments property from model binding. This doesn't require any change to the code that calls TryUpdateModel because you're using the whitelisting overload and CourseAssignments isn't in the include list.

If no check boxes were selected, the code in UpdateInstructorCourses initializes the CourseAssignments navigation property with an empty collection and returns:

if (selectedCourses == null)
{
    instructorToUpdate.CourseAssignments = new List<CourseAssignment>();
    return;
}

The code then loops through all courses in the database and checks each course against the ones currently assigned to the instructor versus the ones that were selected in the page. To facilitate efficient lookups, the latter two collections are stored in HashSet objects.

If the check box for a course was selected but the course isn't in the Instructor.CourseAssignments navigation property, the course is added to the collection in the navigation property.

if (selectedCoursesHS.Contains(course.CourseID.ToString()))
{
    if (!instructorCourses.Contains(course.CourseID))
    {
        instructorToUpdate.CourseAssignments.Add(
            new CourseAssignment
            {
                InstructorID = instructorToUpdate.ID,
                CourseID = course.CourseID
            });
    }
}

If the check box for a course wasn't selected, but the course is in the Instructor.CourseAssignments navigation property, the course is removed from the navigation property.

else
{
    if (instructorCourses.Contains(course.CourseID))
    {
        CourseAssignment courseToRemove
            = instructorToUpdate
                .CourseAssignments
                .SingleOrDefault(i => i.CourseID == course.CourseID);
        context.Remove(courseToRemove);
    }
}

Handle office location

Another relationship the edit page has to handle is the one-to-zero-or-one relationship that the Instructor entity has with the OfficeAssignment entity. The instructor edit code must handle the following scenarios:

  • If the user clears the office assignment, delete the OfficeAssignment entity.
  • If the user enters an office assignment and it was empty, create a new OfficeAssignment entity.
  • If the user changes the office assignment, update the OfficeAssignment entity.

Update the Instructor Edit page model

Update Pages/Instructors/Edit.cshtml.cs with the following code:

using ContosoUniversity.Models;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using System;
using System.Threading.Tasks;

namespace ContosoUniversity.Pages.Instructors
{
    public class EditModel : InstructorCoursesPageModel
    {
        private readonly ContosoUniversity.Data.SchoolContext _context;

        public EditModel(ContosoUniversity.Data.SchoolContext context)
        {
            _context = context;
        }

        [BindProperty]
        public Instructor Instructor { get; set; }

        public async Task<IActionResult> OnGetAsync(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            Instructor = await _context.Instructors
                .Include(i => i.OfficeAssignment)
                .Include(i => i.CourseAssignments).ThenInclude(i => i.Course)
                .AsNoTracking()
                .FirstOrDefaultAsync(m => m.ID == id);

            if (Instructor == null)
            {
                return NotFound();
            }
            PopulateAssignedCourseData(_context, Instructor);
            return Page();
        }

        public async Task<IActionResult> OnPostAsync(int? id, string[] selectedCourses)
        {
            if (id == null)
            {
                return NotFound();
            }

            var instructorToUpdate = await _context.Instructors
                .Include(i => i.OfficeAssignment)
                .Include(i => i.CourseAssignments)
                    .ThenInclude(i => i.Course)
                .FirstOrDefaultAsync(s => s.ID == id);

            if (instructorToUpdate == null)
            {
                return NotFound();
            }

            if (await TryUpdateModelAsync<Instructor>(
                instructorToUpdate,
                "Instructor",
                i => i.FirstMidName, i => i.LastName,
                i => i.HireDate, i => i.OfficeAssignment))
            {
                if (String.IsNullOrWhiteSpace(
                    instructorToUpdate.OfficeAssignment?.Location))
                {
                    instructorToUpdate.OfficeAssignment = null;
                }
                UpdateInstructorCourses(_context, selectedCourses, instructorToUpdate);
                await _context.SaveChangesAsync();
                return RedirectToPage("./Index");
            }
            UpdateInstructorCourses(_context, selectedCourses, instructorToUpdate);
            PopulateAssignedCourseData(_context, instructorToUpdate);
            return Page();
        }
    }
}

The preceding code:

  • Gets the current Instructor entity from the database using eager loading for the OfficeAssignment, CourseAssignment, and CourseAssignment.Course navigation properties.
  • Updates the retrieved Instructor entity with values from the model binder. TryUpdateModel prevents overposting.
  • If the office location is blank, sets Instructor.OfficeAssignment to null. When Instructor.OfficeAssignment is null, the related row in the OfficeAssignment table is deleted.
  • Calls PopulateAssignedCourseData in OnGetAsync to provide information for the checkboxes using the AssignedCourseData view model class.
  • Calls UpdateInstructorCourses in OnPostAsync to apply information from the checkboxes to the Instructor entity being edited.
  • Calls PopulateAssignedCourseData and UpdateInstructorCourses in OnPostAsync if TryUpdateModel fails. These method calls restore the assigned course data entered on the page when it is redisplayed with an error message.

Update the Instructor Edit Razor page

Update Pages/Instructors/Edit.cshtml with the following code:

@page
@model ContosoUniversity.Pages.Instructors.EditModel
@{
    ViewData["Title"] = "Edit";
}
<h2>Edit</h2>
<h4>Instructor</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form method="post">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <input type="hidden" asp-for="Instructor.ID" />
            <div class="form-group">
                <label asp-for="Instructor.LastName" class="control-label"></label>
                <input asp-for="Instructor.LastName" class="form-control" />
                <span asp-validation-for="Instructor.LastName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.FirstMidName" class="control-label"></label>
                <input asp-for="Instructor.FirstMidName" class="form-control" />
                <span asp-validation-for="Instructor.FirstMidName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.HireDate" class="control-label"></label>
                <input asp-for="Instructor.HireDate" class="form-control" />
                <span asp-validation-for="Instructor.HireDate" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.OfficeAssignment.Location" class="control-label"></label>
                <input asp-for="Instructor.OfficeAssignment.Location" class="form-control" />
                <span asp-validation-for="Instructor.OfficeAssignment.Location" class="text-danger" />
            </div>
            <div class="form-group">
                <div class="table">
                    <table>
                        <tr>
                            @{
                                int cnt = 0;

                                foreach (var course in Model.AssignedCourseDataList)
                                {
                                    if (cnt++ % 3 == 0)
                                    {
                                        @:</tr><tr>
                                    }
                                    @:<td>
                                        <input type="checkbox"
                                               name="selectedCourses"
                                               value="@course.CourseID"
                                               @(Html.Raw(course.Assigned ? "checked=\"checked\"" : "")) />
                                               @course.CourseID @:  @course.Title
                                    @:</td>
                                }
                                @:</tr>
                            }
                    </table>
                </div>
            </div>
            <div class="form-group">
                <input type="submit" value="Save" class="btn btn-primary" />
            </div>
        </form>
    </div>
</div>

<div>
    <a asp-page="./Index">Back to List</a>
</div>

@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

The preceding code creates an HTML table that has three columns. Each column has a checkbox and a caption containing the course number and title. The checkboxes all have the same name ("selectedCourses"). Using the same name informs the model binder to treat them as a group. The value attribute of each checkbox is set to CourseID. When the page is posted, the model binder passes an array that consists of the CourseID values for only the checkboxes that are selected.

When the checkboxes are initially rendered, courses assigned to the instructor are selected.

Note: The approach taken here to edit instructor course data works well when there's a limited number of courses. For collections that are much larger, a different UI and a different updating method would be more useable and efficient.

Run the app and test the updated Instructors Edit page. Change some course assignments. The changes are reflected on the Index page.

Update the Instructor Create page

Update the Instructor Create page model and Razor page with code similar to the Edit page:

using ContosoUniversity.Models;
using Microsoft.AspNetCore.Mvc;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace ContosoUniversity.Pages.Instructors
{
    public class CreateModel : InstructorCoursesPageModel
    {
        private readonly ContosoUniversity.Data.SchoolContext _context;

        public CreateModel(ContosoUniversity.Data.SchoolContext context)
        {
            _context = context;
        }

        public IActionResult OnGet()
        {
            var instructor = new Instructor();
            instructor.CourseAssignments = new List<CourseAssignment>();

            // Provides an empty collection for the foreach loop
            // foreach (var course in Model.AssignedCourseDataList)
            // in the Create Razor page.
            PopulateAssignedCourseData(_context, instructor);
            return Page();
        }

        [BindProperty]
        public Instructor Instructor { get; set; }

        public async Task<IActionResult> OnPostAsync(string[] selectedCourses)
        {
            var newInstructor = new Instructor();
            if (selectedCourses != null)
            {
                newInstructor.CourseAssignments = new List<CourseAssignment>();
                foreach (var course in selectedCourses)
                {
                    var courseToAdd = new CourseAssignment
                    {
                        CourseID = int.Parse(course)
                    };
                    newInstructor.CourseAssignments.Add(courseToAdd);
                }
            }

            if (await TryUpdateModelAsync<Instructor>(
                newInstructor,
                "Instructor",
                i => i.FirstMidName, i => i.LastName,
                i => i.HireDate, i => i.OfficeAssignment))
            {
                _context.Instructors.Add(newInstructor);                
                await _context.SaveChangesAsync();
                return RedirectToPage("./Index");
            }
            PopulateAssignedCourseData(_context, newInstructor);
            return Page();
        }
    }
}
@page
@model ContosoUniversity.Pages.Instructors.CreateModel

@{
    ViewData["Title"] = "Create";
}

<h2>Create</h2>

<h4>Instructor</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form method="post">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <div class="form-group">
                <label asp-for="Instructor.LastName" class="control-label"></label>
                <input asp-for="Instructor.LastName" class="form-control" />
                <span asp-validation-for="Instructor.LastName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.FirstMidName" class="control-label"></label>
                <input asp-for="Instructor.FirstMidName" class="form-control" />
                <span asp-validation-for="Instructor.FirstMidName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.HireDate" class="control-label"></label>
                <input asp-for="Instructor.HireDate" class="form-control" />
                <span asp-validation-for="Instructor.HireDate" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.OfficeAssignment.Location" class="control-label"></label>
                <input asp-for="Instructor.OfficeAssignment.Location" class="form-control" />
                <span asp-validation-for="Instructor.OfficeAssignment.Location" class="text-danger" />
            </div>
            <div class="form-group">
                <div class="table">
                    <table>
                        <tr>
                            @{
                                int cnt = 0;

                                foreach (var course in Model.AssignedCourseDataList)
                                {
                                    if (cnt++ % 3 == 0)
                                    {
                                        @:</tr><tr>
                                    }
                                    @:<td>
                                        <input type="checkbox"
                                               name="selectedCourses"
                                               value="@course.CourseID"
                                               @(Html.Raw(course.Assigned ? "checked=\"checked\"" : "")) />
                                               @course.CourseID @:  @course.Title
                                    @:</td>
                                }
                                @:</tr>
                            }
                    </table>
                </div>
            </div>
            <div class="form-group">
                <input type="submit" value="Create" class="btn btn-primary" />
            </div>
        </form>
    </div>
</div>

<div>
    <a asp-page="Index">Back to List</a>
</div>

@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

Test the instructor Create page.

Update the Instructor Delete page

Update Pages/Instructors/Delete.cshtml.cs with the following code:

using ContosoUniversity.Models;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.EntityFrameworkCore;
using System.Linq;
using System.Threading.Tasks;

namespace ContosoUniversity.Pages.Instructors
{
    public class DeleteModel : PageModel
    {
        private readonly ContosoUniversity.Data.SchoolContext _context;

        public DeleteModel(ContosoUniversity.Data.SchoolContext context)
        {
            _context = context;
        }

        [BindProperty]
        public Instructor Instructor { get; set; }

        public async Task<IActionResult> OnGetAsync(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            Instructor = await _context.Instructors.FirstOrDefaultAsync(m => m.ID == id);

            if (Instructor == null)
            {
                return NotFound();
            }
            return Page();
        }

        public async Task<IActionResult> OnPostAsync(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            Instructor instructor = await _context.Instructors
                .Include(i => i.CourseAssignments)
                .SingleAsync(i => i.ID == id);

            if (instructor == null)
            {
                return RedirectToPage("./Index");
            }

            var departments = await _context.Departments
                .Where(d => d.InstructorID == id)
                .ToListAsync();
            departments.ForEach(d => d.InstructorID = null);

            _context.Instructors.Remove(instructor);

            await _context.SaveChangesAsync();
            return RedirectToPage("./Index");
        }
    }
}

The preceding code makes the following changes:

  • Uses eager loading for the CourseAssignments navigation property. CourseAssignments must be included or they aren't deleted when the instructor is deleted. To avoid needing to read them, configure cascade delete in the database.

  • If the instructor to be deleted is assigned as administrator of any departments, removes the instructor assignment from those departments.

Run the app and test the Delete page.

Next steps

This tutorial demonstrates updating related data. If you run into problems you can't solve, download or view the completed app. Download instructions.

The following illustrations shows some of the completed pages.

Course Edit page Instructor Edit page

Examine and test the Create and Edit course pages. Create a new course. The department is selected by its primary key (an integer), not its name. Edit the new course. When you have finished testing, delete the new course.

Create a base class to share common code

The Courses/Create and Courses/Edit pages each need a list of department names. Create the Pages/Courses/DepartmentNamePageModel.cshtml.cs base class for the Create and Edit pages:

using ContosoUniversity.Data;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.EntityFrameworkCore;
using System.Linq;

namespace ContosoUniversity.Pages.Courses
{
    public class DepartmentNamePageModel : PageModel
    {
        public SelectList DepartmentNameSL { get; set; }

        public void PopulateDepartmentsDropDownList(SchoolContext _context,
            object selectedDepartment = null)
        {
            var departmentsQuery = from d in _context.Departments
                                   orderby d.Name // Sort by name.
                                   select d;

            DepartmentNameSL = new SelectList(departmentsQuery.AsNoTracking(),
                        "DepartmentID", "Name", selectedDepartment);
        }
    }
}

The preceding code creates a SelectList to contain the list of department names. If selectedDepartment is specified, that department is selected in the SelectList.

The Create and Edit page model classes will derive from DepartmentNamePageModel.

Customize the Courses Pages

When a new course entity is created, it must have a relationship to an existing department. To add a department while creating a course, the base class for Create and Edit contains a drop-down list for selecting the department. The drop-down list sets the Course.DepartmentID foreign key (FK) property. EF Core uses the Course.DepartmentID FK to load the Department navigation property.

Create course

Update the Create page model with the following code:

using ContosoUniversity.Models;
using Microsoft.AspNetCore.Mvc;
using System.Threading.Tasks;

namespace ContosoUniversity.Pages.Courses
{
    public class CreateModel : DepartmentNamePageModel
    {
        private readonly ContosoUniversity.Data.SchoolContext _context;

        public CreateModel(ContosoUniversity.Data.SchoolContext context)
        {
            _context = context;
        }

        public IActionResult OnGet()
        {
            PopulateDepartmentsDropDownList(_context);
            return Page();
        }

        [BindProperty]
        public Course Course { get; set; }

        public async Task<IActionResult> OnPostAsync()
        {
            if (!ModelState.IsValid)
            {
                return Page();
            }

            var emptyCourse = new Course();

            if (await TryUpdateModelAsync<Course>(
                 emptyCourse,
                 "course",   // Prefix for form value.
                 s => s.CourseID, s => s.DepartmentID, s => s.Title, s => s.Credits))
            {
                _context.Courses.Add(emptyCourse);
                await _context.SaveChangesAsync();
                return RedirectToPage("./Index");
            }

            // Select DepartmentID if TryUpdateModelAsync fails.
            PopulateDepartmentsDropDownList(_context, emptyCourse.DepartmentID);
            return Page();
        }
      }
}

The preceding code:

  • Derives from DepartmentNamePageModel.
  • Uses TryUpdateModelAsync to prevent overposting.
  • Replaces ViewData["DepartmentID"] with DepartmentNameSL (from the base class).

ViewData["DepartmentID"] is replaced with the strongly typed DepartmentNameSL. Strongly typed models are preferred over weakly typed. For more information, see Weakly typed data (ViewData and ViewBag).

Update the Courses Create page

Update Pages/Courses/Create.cshtml with the following code:

@page
@model ContosoUniversity.Pages.Courses.CreateModel
@{
    ViewData["Title"] = "Create Course";
}
<h2>Create</h2>
<h4>Course</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form method="post">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <div class="form-group">
                <label asp-for="Course.CourseID" class="control-label"></label>
                <input asp-for="Course.CourseID" class="form-control" />
                <span asp-validation-for="Course.CourseID" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Course.Title" class="control-label"></label>
                <input asp-for="Course.Title" class="form-control" />
                <span asp-validation-for="Course.Title" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Course.Credits" class="control-label"></label>
                <input asp-for="Course.Credits" class="form-control" />
                <span asp-validation-for="Course.Credits" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Course.Department" class="control-label"></label>
                <select asp-for="Course.DepartmentID" class="form-control"
                        asp-items="@Model.DepartmentNameSL">
                    <option value="">-- Select Department --</option>
                </select>
                <span asp-validation-for="Course.DepartmentID" class="text-danger" />
            </div>
            <div class="form-group">
                <input type="submit" value="Create" class="btn btn-default" />
            </div>
        </form>
    </div>
</div>
<div>
    <a asp-page="Index">Back to List</a>
</div>
@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

The preceding markup makes the following changes:

  • Changes the caption from DepartmentID to Department.
  • Replaces "ViewBag.DepartmentID" with DepartmentNameSL (from the base class).
  • Adds the "Select Department" option. This change renders "Select Department" rather than the first department.
  • Adds a validation message when the department isn't selected.

The Razor Page uses the Select Tag Helper:

<div class="form-group">
    <label asp-for="Course.Department" class="control-label"></label>
    <select asp-for="Course.DepartmentID" class="form-control"
            asp-items="@Model.DepartmentNameSL">
        <option value="">-- Select Department --</option>
    </select>
    <span asp-validation-for="Course.DepartmentID" class="text-danger" />
</div>

Test the Create page. The Create page displays the department name rather than the department ID.

Update the Courses Edit page.

Replace the code in Pages/Courses/Edit.cshtml.cs with the following code:

using ContosoUniversity.Models;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using System.Threading.Tasks;

namespace ContosoUniversity.Pages.Courses
{
    public class EditModel : DepartmentNamePageModel
    {
        private readonly ContosoUniversity.Data.SchoolContext _context;

        public EditModel(ContosoUniversity.Data.SchoolContext context)
        {
            _context = context;
        }

        [BindProperty]
        public Course Course { get; set; }

        public async Task<IActionResult> OnGetAsync(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            Course = await _context.Courses
                .Include(c => c.Department).FirstOrDefaultAsync(m => m.CourseID == id);

            if (Course == null)
            {
                return NotFound();
            }

            // Select current DepartmentID.
            PopulateDepartmentsDropDownList(_context,Course.DepartmentID);
            return Page();
        }

        public async Task<IActionResult> OnPostAsync(int? id)
        {
            if (!ModelState.IsValid)
            {
                return Page();
            }

            var courseToUpdate = await _context.Courses.FindAsync(id);

            if (await TryUpdateModelAsync<Course>(
                 courseToUpdate,
                 "course",   // Prefix for form value.
                   c => c.Credits, c => c.DepartmentID, c => c.Title))
            {
                await _context.SaveChangesAsync();
                return RedirectToPage("./Index");
            }

            // Select DepartmentID if TryUpdateModelAsync fails.
            PopulateDepartmentsDropDownList(_context, courseToUpdate.DepartmentID);
            return Page();
        }       
    }
}

The changes are similar to those made in the Create page model. In the preceding code, PopulateDepartmentsDropDownList passes in the department ID, which select the department specified in the drop-down list.

Update Pages/Courses/Edit.cshtml with the following markup:

@page
@model ContosoUniversity.Pages.Courses.EditModel

@{
    ViewData["Title"] = "Edit";
}

<h2>Edit</h2>

<h4>Course</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form method="post">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <input type="hidden" asp-for="Course.CourseID" />
            <div class="form-group">
                <label asp-for="Course.CourseID" class="control-label"></label>
                <div>@Html.DisplayFor(model => model.Course.CourseID)</div>
            </div>
            <div class="form-group">
                <label asp-for="Course.Title" class="control-label"></label>
                <input asp-for="Course.Title" class="form-control" />
                <span asp-validation-for="Course.Title" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Course.Credits" class="control-label"></label>
                <input asp-for="Course.Credits" class="form-control" />
                <span asp-validation-for="Course.Credits" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Course.Department" class="control-label"></label>
                <select asp-for="Course.DepartmentID" class="form-control" 
                        asp-items="@Model.DepartmentNameSL"></select>
                <span asp-validation-for="Course.DepartmentID" class="text-danger"></span>
            </div>
            <div class="form-group">
                <input type="submit" value="Save" class="btn btn-default" />
            </div>
        </form>
    </div>
</div>

<div>
    <a asp-page="./Index">Back to List</a>
</div>

@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

The preceding markup makes the following changes:

  • Displays the course ID. Generally the Primary Key (PK) of an entity isn't displayed. PKs are usually meaningless to users. In this case, the PK is the course number.
  • Changes the caption from DepartmentID to Department.
  • Replaces "ViewBag.DepartmentID" with DepartmentNameSL (from the base class).

The page contains a hidden field (<input type="hidden">) for the course number. Adding a <label> tag helper with asp-for="Course.CourseID" doesn't eliminate the need for the hidden field. <input type="hidden"> is required for the course number to be included in the posted data when the user clicks Save.

Test the updated code. Create, edit, and delete a course.

Add AsNoTracking to the Details and Delete page models

AsNoTracking can improve performance when tracking isn't required. Add AsNoTracking to the Delete and Details page model. The following code shows the updated Delete page model:

public class DeleteModel : PageModel
{
    private readonly ContosoUniversity.Data.SchoolContext _context;

    public DeleteModel(ContosoUniversity.Data.SchoolContext context)
    {
        _context = context;
    }

    [BindProperty]
    public Course Course { get; set; }

    public async Task<IActionResult> OnGetAsync(int? id)
    {
        if (id == null)
        {
            return NotFound();
        }

        Course = await _context.Courses
            .AsNoTracking()
            .Include(c => c.Department)
            .FirstOrDefaultAsync(m => m.CourseID == id);

        if (Course == null)
        {
            return NotFound();
        }
        return Page();
    }

    public async Task<IActionResult> OnPostAsync(int? id)
    {
        if (id == null)
        {
            return NotFound();
        }

        Course = await _context.Courses
            .AsNoTracking()
            .FirstOrDefaultAsync(m => m.CourseID == id);

        if (Course != null)
        {
            _context.Courses.Remove(Course);
            await _context.SaveChangesAsync();
        }

        return RedirectToPage("./Index");
    }
}

Update the OnGetAsync method in the Pages/Courses/Details.cshtml.cs file:

public async Task<IActionResult> OnGetAsync(int? id)
{
    if (id == null)
    {
        return NotFound();
    }

    Course = await _context.Courses
         .AsNoTracking()
         .Include(c => c.Department)
         .FirstOrDefaultAsync(m => m.CourseID == id);

    if (Course == null)
    {
        return NotFound();
    }
    return Page();
}

Modify the Delete and Details pages

Update the Delete Razor page with the following markup:

@page
@model ContosoUniversity.Pages.Courses.DeleteModel

@{
    ViewData["Title"] = "Delete";
}

<h2>Delete</h2>

<h3>Are you sure you want to delete this?</h3>
<div>
    <h4>Course</h4>
    <hr />
    <dl class="dl-horizontal">
        <dt>
            @Html.DisplayNameFor(model => model.Course.CourseID)
        </dt>
        <dd>
            @Html.DisplayFor(model => model.Course.CourseID)
        </dd>
        <dt>
            @Html.DisplayNameFor(model => model.Course.Title)
        </dt>
        <dd>
            @Html.DisplayFor(model => model.Course.Title)
        </dd>
        <dt>
            @Html.DisplayNameFor(model => model.Course.Credits)
        </dt>
        <dd>
            @Html.DisplayFor(model => model.Course.Credits)
        </dd>
        <dt>
            @Html.DisplayNameFor(model => model.Course.Department)
        </dt>
        <dd>
            @Html.DisplayFor(model => model.Course.Department.DepartmentID)
        </dd>
    </dl>
    
    <form method="post">
        <input type="hidden" asp-for="Course.CourseID" />
        <input type="submit" value="Delete" class="btn btn-default" /> |
        <a asp-page="./Index">Back to List</a>
    </form>
</div>

Make the same changes to the Details page.

Test the Course pages

Test create, edit, details, and delete.

Update the instructor pages

The following sections update the instructor pages.

Add office location

When editing an instructor record, you may want to update the instructor's office assignment. The Instructor entity has a one-to-zero-or-one relationship with the OfficeAssignment entity. The instructor code must handle:

  • If the user clears the office assignment, delete the OfficeAssignment entity.
  • If the user enters an office assignment and it was empty, create a new OfficeAssignment entity.
  • If the user changes the office assignment, update the OfficeAssignment entity.

Update the instructors Edit page model with the following code:

public class EditModel : PageModel
{
    private readonly ContosoUniversity.Data.SchoolContext _context;

    public EditModel(ContosoUniversity.Data.SchoolContext context)
    {
        _context = context;
    }

    [BindProperty]
    public Instructor Instructor { get; set; }

    public async Task<IActionResult> OnGetAsync(int? id)
    {
        if (id == null)
        {
            return NotFound();
        }

        Instructor = await _context.Instructors
            .Include(i => i.OfficeAssignment)
            .AsNoTracking()
            .FirstOrDefaultAsync(m => m.ID == id);

        if (Instructor == null)
        {
            return NotFound();
        }
        return Page();
    }

    public async Task<IActionResult> OnPostAsync(int? id)
    {
        if (!ModelState.IsValid)
        {
            return Page();
        }

        var instructorToUpdate = await _context.Instructors
            .Include(i => i.OfficeAssignment)
            .FirstOrDefaultAsync(s => s.ID == id);

        if (await TryUpdateModelAsync<Instructor>(
            instructorToUpdate,
            "Instructor",
            i => i.FirstMidName, i => i.LastName, 
            i => i.HireDate, i => i.OfficeAssignment))
        {
            if (String.IsNullOrWhiteSpace(
                instructorToUpdate.OfficeAssignment?.Location))
            {
                instructorToUpdate.OfficeAssignment = null;
            }
            await _context.SaveChangesAsync();
        }
        return RedirectToPage("./Index");

    }
}

The preceding code:

  • Gets the current Instructor entity from the database using eager loading for the OfficeAssignment navigation property.
  • Updates the retrieved Instructor entity with values from the model binder. TryUpdateModel prevents overposting.
  • If the office location is blank, sets Instructor.OfficeAssignment to null. When Instructor.OfficeAssignment is null, the related row in the OfficeAssignment table is deleted.

Update the instructor Edit page

Update Pages/Instructors/Edit.cshtml with the office location:

@page
@model ContosoUniversity.Pages.Instructors.EditModel
@{
    ViewData["Title"] = "Edit";
}
<h2>Edit</h2>
<h4>Instructor</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form method="post">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <input type="hidden" asp-for="Instructor.ID" />
            <div class="form-group">
                <label asp-for="Instructor.LastName" class="control-label"></label>
                <input asp-for="Instructor.LastName" class="form-control" />
                <span asp-validation-for="Instructor.LastName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.FirstMidName" class="control-label"></label>
                <input asp-for="Instructor.FirstMidName" class="form-control" />
                <span asp-validation-for="Instructor.FirstMidName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.HireDate" class="control-label"></label>
                <input asp-for="Instructor.HireDate" class="form-control" />
                <span asp-validation-for="Instructor.HireDate" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.OfficeAssignment.Location" class="control-label"></label>
                <input asp-for="Instructor.OfficeAssignment.Location" class="form-control" />
                <span asp-validation-for="Instructor.OfficeAssignment.Location" class="text-danger" />
            </div>
            <div class="form-group">
                <input type="submit" value="Save" class="btn btn-default" />
            </div>
        </form>
    </div>
</div>

<div>
    <a asp-page="./Index">Back to List</a>
</div>

@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

Verify you can change an instructors office location.

Add Course assignments to the instructor Edit page

Instructors may teach any number of courses. In this section, you add the ability to change course assignments. The following image shows the updated instructor Edit page:

Instructor Edit page with courses

Course and Instructor has a many-to-many relationship. To add and remove relationships, you add and remove entities from the CourseAssignments join entity set.

Check boxes enable changes to courses an instructor is assigned to. A check box is displayed for every course in the database. Courses that the instructor is assigned to are checked. The user can select or clear check boxes to change course assignments. If the number of courses were much greater:

  • You'd probably use a different user interface to display the courses.
  • The method of manipulating a join entity to create or delete relationships wouldn't change.

Add classes to support Create and Edit instructor pages

Create SchoolViewModels/AssignedCourseData.cs with the following code:

namespace ContosoUniversity.Models.SchoolViewModels
{
    public class AssignedCourseData
    {
        public int CourseID { get; set; }
        public string Title { get; set; }
        public bool Assigned { get; set; }
    }
}

The AssignedCourseData class contains data to create the check boxes for assigned courses by an instructor.

Create the Pages/Instructors/InstructorCoursesPageModel.cshtml.cs base class:

using ContosoUniversity.Data;
using ContosoUniversity.Models;
using ContosoUniversity.Models.SchoolViewModels;
using Microsoft.AspNetCore.Mvc.RazorPages;
using System.Collections.Generic;
using System.Linq;

namespace ContosoUniversity.Pages.Instructors
{
    public class InstructorCoursesPageModel : PageModel
    {

        public List<AssignedCourseData> AssignedCourseDataList;

        public void PopulateAssignedCourseData(SchoolContext context, 
                                               Instructor instructor)
        {
            var allCourses = context.Courses;
            var instructorCourses = new HashSet<int>(
                instructor.CourseAssignments.Select(c => c.CourseID));
            AssignedCourseDataList = new List<AssignedCourseData>();
            foreach (var course in allCourses)
            {
                AssignedCourseDataList.Add(new AssignedCourseData
                {
                    CourseID = course.CourseID,
                    Title = course.Title,
                    Assigned = instructorCourses.Contains(course.CourseID)
                });
            }
        }

        public void UpdateInstructorCourses(SchoolContext context, 
            string[] selectedCourses, Instructor instructorToUpdate)
        {
            if (selectedCourses == null)
            {
                instructorToUpdate.CourseAssignments = new List<CourseAssignment>();
                return;
            }

            var selectedCoursesHS = new HashSet<string>(selectedCourses);
            var instructorCourses = new HashSet<int>
                (instructorToUpdate.CourseAssignments.Select(c => c.Course.CourseID));
            foreach (var course in context.Courses)
            {
                if (selectedCoursesHS.Contains(course.CourseID.ToString()))
                {
                    if (!instructorCourses.Contains(course.CourseID))
                    {
                        instructorToUpdate.CourseAssignments.Add(
                            new CourseAssignment
                            {
                                InstructorID = instructorToUpdate.ID,
                                CourseID = course.CourseID
                            });
                    }
                }
                else
                {
                    if (instructorCourses.Contains(course.CourseID))
                    {
                        CourseAssignment courseToRemove
                            = instructorToUpdate
                                .CourseAssignments
                                .SingleOrDefault(i => i.CourseID == course.CourseID);
                        context.Remove(courseToRemove);
                    }
                }
            }
        }
    }
}

The InstructorCoursesPageModel is the base class you will use for the Edit and Create page models. PopulateAssignedCourseData reads all Course entities to populate AssignedCourseDataList. For each course, the code sets the CourseID, title, and whether or not the instructor is assigned to the course. A HashSet is used to create efficient lookups.

Instructors Edit page model

Update the instructor Edit page model with the following code:

public class EditModel : InstructorCoursesPageModel
{
    private readonly ContosoUniversity.Data.SchoolContext _context;

    public EditModel(ContosoUniversity.Data.SchoolContext context)
    {
        _context = context;
    }

    [BindProperty]
    public Instructor Instructor { get; set; }

    public async Task<IActionResult> OnGetAsync(int? id)
    {
        if (id == null)
        {
            return NotFound();
        }

        Instructor = await _context.Instructors
            .Include(i => i.OfficeAssignment)
            .Include(i => i.CourseAssignments).ThenInclude(i => i.Course)
            .AsNoTracking()
            .FirstOrDefaultAsync(m => m.ID == id);

        if (Instructor == null)
        {
            return NotFound();
        }
        PopulateAssignedCourseData(_context, Instructor);
        return Page();
    }

    public async Task<IActionResult> OnPostAsync(int? id, string[] selectedCourses)
    {
        if (!ModelState.IsValid)
        {
            return Page();
        }

        var instructorToUpdate = await _context.Instructors
            .Include(i => i.OfficeAssignment)
            .Include(i => i.CourseAssignments)
                .ThenInclude(i => i.Course)
            .FirstOrDefaultAsync(s => s.ID == id);

        if (await TryUpdateModelAsync<Instructor>(
            instructorToUpdate,
            "Instructor",
            i => i.FirstMidName, i => i.LastName,
            i => i.HireDate, i => i.OfficeAssignment))
        {
            if (String.IsNullOrWhiteSpace(
                instructorToUpdate.OfficeAssignment?.Location))
            {
                instructorToUpdate.OfficeAssignment = null;
            }
            UpdateInstructorCourses(_context, selectedCourses, instructorToUpdate);
            await _context.SaveChangesAsync();
            return RedirectToPage("./Index");
        }
        UpdateInstructorCourses(_context, selectedCourses, instructorToUpdate);
        PopulateAssignedCourseData(_context, instructorToUpdate);
        return Page();
    }
}

The preceding code handles office assignment changes.

Update the instructor Razor View:

@page
@model ContosoUniversity.Pages.Instructors.EditModel
@{
    ViewData["Title"] = "Edit";
}
<h2>Edit</h2>
<h4>Instructor</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form method="post">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <input type="hidden" asp-for="Instructor.ID" />
            <div class="form-group">
                <label asp-for="Instructor.LastName" class="control-label"></label>
                <input asp-for="Instructor.LastName" class="form-control" />
                <span asp-validation-for="Instructor.LastName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.FirstMidName" class="control-label"></label>
                <input asp-for="Instructor.FirstMidName" class="form-control" />
                <span asp-validation-for="Instructor.FirstMidName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.HireDate" class="control-label"></label>
                <input asp-for="Instructor.HireDate" class="form-control" />
                <span asp-validation-for="Instructor.HireDate" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.OfficeAssignment.Location" class="control-label"></label>
                <input asp-for="Instructor.OfficeAssignment.Location" class="form-control" />
                <span asp-validation-for="Instructor.OfficeAssignment.Location" class="text-danger" />
            </div>
            <div class="form-group">
                <div class="col-md-offset-2 col-md-10">
                    <table>
                        <tr>
                            @{
                                int cnt = 0;

                                foreach (var course in Model.AssignedCourseDataList)
                                {
                                    if (cnt++ % 3 == 0)
                                    {
                                        @:</tr><tr>
                                    }
                                    @:<td>
                                        <input type="checkbox"
                                               name="selectedCourses"
                                               value="@course.CourseID"
                                               @(Html.Raw(course.Assigned ? "checked=\"checked\"" : "")) />
                                               @course.CourseID @:  @course.Title
                                    @:</td>
                                }
                                @:</tr>
                            }
                    </table>
                </div>
            </div>
            <div class="form-group">
                <input type="submit" value="Save" class="btn btn-default" />
            </div>
        </form>
    </div>
</div>

<div>
    <a asp-page="./Index">Back to List</a>
</div>

@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

Note

When you paste the code in Visual Studio, line breaks are changed in a way that breaks the code. Press Ctrl+Z one time to undo the automatic formatting. Ctrl+Z fixes the line breaks so that they look like what you see here. The indentation doesn't have to be perfect, but the @:</tr><tr>, @:<td>, @:</td>, and @:</tr> lines must each be on a single line as shown. With the block of new code selected, press Tab three times to line up the new code with the existing code. Vote on or review the status of this bug with this link.

The preceding code creates an HTML table that has three columns. Each column has a check box and a caption containing the course number and title. The check boxes all have the same name ("selectedCourses"). Using the same name informs the model binder to treat them as a group. The value attribute of each check box is set to CourseID. When the page is posted, the model binder passes an array that consists of the CourseID values for only the check boxes that are selected.

When the check boxes are initially rendered, courses assigned to the instructor have checked attributes.

Run the app and test the updated instructors Edit page. Change some course assignments. The changes are reflected on the Index page.

Note: The approach taken here to edit instructor course data works well when there's a limited number of courses. For collections that are much larger, a different UI and a different updating method would be more useable and efficient.

Update the instructors Create page

Update the instructor Create page model with the following code:

using ContosoUniversity.Models;
using Microsoft.AspNetCore.Mvc;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace ContosoUniversity.Pages.Instructors
{
    public class CreateModel : InstructorCoursesPageModel
    {
        private readonly ContosoUniversity.Data.SchoolContext _context;

        public CreateModel(ContosoUniversity.Data.SchoolContext context)
        {
            _context = context;
        }

        public IActionResult OnGet()
        {
            var instructor = new Instructor();
            instructor.CourseAssignments = new List<CourseAssignment>();

            // Provides an empty collection for the foreach loop
            // foreach (var course in Model.AssignedCourseDataList)
            // in the Create Razor page.
            PopulateAssignedCourseData(_context, instructor);
            return Page();
        }

        [BindProperty]
        public Instructor Instructor { get; set; }

        public async Task<IActionResult> OnPostAsync(string[] selectedCourses)
        {
            if (!ModelState.IsValid)
            {
                return Page();
            }

            var newInstructor = new Instructor();
            if (selectedCourses != null)
            {
                newInstructor.CourseAssignments = new List<CourseAssignment>();
                foreach (var course in selectedCourses)
                {
                    var courseToAdd = new CourseAssignment
                    {
                        CourseID = int.Parse(course)
                    };
                    newInstructor.CourseAssignments.Add(courseToAdd);
                }
            }

            if (await TryUpdateModelAsync<Instructor>(
                newInstructor,
                "Instructor",
                i => i.FirstMidName, i => i.LastName,
                i => i.HireDate, i => i.OfficeAssignment))
            {
                _context.Instructors.Add(newInstructor);                
                await _context.SaveChangesAsync();
                return RedirectToPage("./Index");
            }
            PopulateAssignedCourseData(_context, newInstructor);
            return Page();
        }
    }
}

The preceding code is similar to the Pages/Instructors/Edit.cshtml.cs code.

Update the instructor Create Razor page with the following markup:

@page
@model ContosoUniversity.Pages.Instructors.CreateModel

@{
    ViewData["Title"] = "Create";
}

<h2>Create</h2>

<h4>Instructor</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form method="post">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <div class="form-group">
                <label asp-for="Instructor.LastName" class="control-label"></label>
                <input asp-for="Instructor.LastName" class="form-control" />
                <span asp-validation-for="Instructor.LastName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.FirstMidName" class="control-label"></label>
                <input asp-for="Instructor.FirstMidName" class="form-control" />
                <span asp-validation-for="Instructor.FirstMidName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.HireDate" class="control-label"></label>
                <input asp-for="Instructor.HireDate" class="form-control" />
                <span asp-validation-for="Instructor.HireDate" class="text-danger"></span>
            </div>
            
            <div class="form-group">
                <label asp-for="Instructor.OfficeAssignment.Location" class="control-label"></label>
                <input asp-for="Instructor.OfficeAssignment.Location" class="form-control" />
                <span asp-validation-for="Instructor.OfficeAssignment.Location" class="text-danger" />
            </div>
            <div class="form-group">
                <div class="col-md-offset-2 col-md-10">
                    <table>
                        <tr>
                            @{
                                int cnt = 0;

                                foreach (var course in Model.AssignedCourseDataList)
                                {
                                    if (cnt++ % 3 == 0)
                                    {
                                        @:</tr><tr>
                                    }
                                    @:<td>
                                        <input type="checkbox"
                                               name="selectedCourses"
                                               value="@course.CourseID"
                                               @(Html.Raw(course.Assigned ? "checked=\"checked\"" : "")) />
                                               @course.CourseID @:  @course.Title
                                    @:</td>
                                }
                                @:</tr>
                            }
                    </table>
                </div>
            </div>
            <div class="form-group">
                <input type="submit" value="Create" class="btn btn-default" />
            </div>
        </form>
    </div>
</div>

<div>
    <a asp-page="Index">Back to List</a>
</div>

@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

Test the instructor Create page.

Update the Delete page

Update the Delete page model with the following code:

using ContosoUniversity.Models;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.EntityFrameworkCore;
using System.Linq;
using System.Threading.Tasks;

namespace ContosoUniversity.Pages.Instructors
{
    public class DeleteModel : PageModel
    {
        private readonly ContosoUniversity.Data.SchoolContext _context;

        public DeleteModel(ContosoUniversity.Data.SchoolContext context)
        {
            _context = context;
        }

        [BindProperty]
        public Instructor Instructor { get; set; }

        public async Task<IActionResult> OnGetAsync(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            Instructor = await _context.Instructors.SingleAsync(m => m.ID == id);

            if (Instructor == null)
            {
                return NotFound();
            }
            return Page();
        }

        public async Task<IActionResult> OnPostAsync(int id)
        {
            Instructor instructor = await _context.Instructors
                .Include(i => i.CourseAssignments)
                .SingleAsync(i => i.ID == id);

            var departments = await _context.Departments
                .Where(d => d.InstructorID == id)
                .ToListAsync();
            departments.ForEach(d => d.InstructorID = null);

            _context.Instructors.Remove(instructor);

            await _context.SaveChangesAsync();
            return RedirectToPage("./Index");
        }
    }
}

The preceding code makes the following changes:

  • Uses eager loading for the CourseAssignments navigation property. CourseAssignments must be included or they aren't deleted when the instructor is deleted. To avoid needing to read them, configure cascade delete in the database.

  • If the instructor to be deleted is assigned as administrator of any departments, removes the instructor assignment from those departments.

Additional resources