查詢實體和關聯 (Entity Framework 快速入門)

發行項
08/21/2008

在這項工作中，您將針對代表 School 模型中之實體 (Entity) 和關聯的 CLR 物件建立強型別 (Strongly Typed) 查詢，並且將顯示控制項繫結至從這些查詢傳回的物件集合。

查詢 School 資料庫中的部門

在 CourseViewer 表單的程式碼檔案開頭，加入下列 using (C#) 或 Imports (Visual Basic) 陳述式 (Statement)，以便參考根據 School 資料庫所建立的模型以及實體命名空間 (Namespace)。
```
Imports System.Data.Objects
Imports System.Data.Objects.DataClasses
```
```
using System.Data.Objects;
using System.Data.Objects.DataClasses;
```

在 CourseViewer 表單的部分類別定義頂端，加入下列可建立 ObjectContext 執行個體 (Instance) 的程式碼。

' Create an ObjectContext instance based on SchoolEntity.
Private schoolContext As SchoolEntities

// Create an ObjectContext instance based on SchoolEntity.
private SchoolEntities schoolContext;

在 CourseViewer 表單設計工具中，按兩下 CourseViewer 表單。

這樣會開啟表單的字碼頁 (Code Page) 並且建立 courseViewer _Load 事件處理常式方法。

在 courseViewer _Load 事件處理常式方中，複製並貼上下列可定義 DataGridView 的程式碼、執行可傳回部門集合 (按照 Name 排列順序) 的查詢，然後將 Department 物件的集合繫結至 departmentList 控制項。

' Initialize the ObjectContext.
schoolContext = New SchoolEntities()

' Define a query that returns all Department objects and related
' Course objects, ordered by name.
Dim departmentQuery As ObjectQuery(Of Department) = _
    schoolContext.Department.Include("Course").OrderBy("it.Name")

Try
    ' Bind the ComboBox control to the query, which is 
    ' executed during data binding.
    Me.departmentList.DataSource = departmentQuery
    Me.departmentList.DisplayMember = "Name"
Catch ex As Exception
    MessageBox.Show(ex.Message)
End Try

// Initialize the ObjectContext.
schoolContext = new SchoolEntities();

// Define a query that returns all Department objects and related
// Course objects, ordered by name.
ObjectQuery<Department> departmentQuery =
    schoolContext.Department.Include("Course").OrderBy("it.Name");

try
{
    // Bind the ComboBox control to the query, which is
    // executed during data binding.
    this.departmentList.DataSource = departmentQuery;
    this.departmentList.DisplayMember = "Name";
}
catch (Exception ex)
{
    MessageBox.Show(ex.Message);
}

顯示所選取部門的課程

在 CourseViewer 表單設計工具中，按兩下 departmentList 控制項。

這樣會建立 departmentList_SelectedIndexChanged 事件處理常式方法。

貼上下列用來載入與所選取部門相關之課程的程式碼。

Try
    ' Get the object for the selected department.
    Dim department As Department = _
        CType(Me.departmentList.SelectedItem, Department)

    ' Bind the grid view to the collection of Course objects 
    ' that are related to the selected Department object.
    courseGridView.DataSource = department.Course
    courseGridView.AutoResizeColumns(DataGridViewAutoSizeColumnsMode.AllCells)
Catch ex As Exception
    MessageBox.Show(ex.Message)
End Try

try
{
    // Get the object for the selected department.
    Department department = 
        (Department)this.departmentList.SelectedItem;

    // Bind the grid view to the collection of Course objects 
    // that are related to the selected Department object.
    courseGridView.DataSource = department.Course;

    courseGridView.AutoResizeColumns(DataGridViewAutoSizeColumnsMode.AllCells);
}
catch (Exception ex)
{
    MessageBox.Show(ex.Message);
}

後續的步驟

您已成功建立可傳回 Department 和 Course 物件的查詢，並且將這些物件繫結至控制項。接下來，請將您對資料格中 Course 物件做的變更儲存回資料庫：插入及更新資料 (Entity Framework 快速入門)。

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查詢實體和關聯 (Entity Framework 快速入門)

查詢 School 資料庫中的部門

顯示所選取部門的課程

後續的步驟

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