Exercise - Reverse engineering - Learn

8 minutes

ContosoPizza's manager has asked you to add an endpoint to list coupons from an existing database. In this unit, you'll create scaffolding from an existing database and modify the resulting entity class.

Inspect promotions database

In the EXPLORER pane, right-click on Promotions/Promotions.db file and select Open Database.
In the SQLITE EXPLORER pane, expand the Promotions.db and Coupons nodes. Note the data schema.
Right-click the Coupons node and select Show table. Inspect the coupon data.

Scaffold the promotions context and coupon model

Run the following command:
```
dotnet ef dbcontext scaffold "Data Source=.\Promotions\Promotions.db" Microsoft.EntityFrameworkCore.Sqlite --context-dir .\Data --output-dir .\Models   
```
The preceding command:
- Scaffolds a DbContext and model classes using the provided connection string.
- Specifies the Microsoft.EntityFrameworkCore.Sqlite database provider should be used.
- Specifies directories for the resulting DbContext and model classes.
Open Models\Coupon.cs. The Expiration property is defined as a string, since SQLite doesn't have a datetime type. Change Expiration's type from a string? to a DateTime. EF Core will manage the conversion of datetime to string data.
```
using System;
using System.Collections.Generic;

namespace ContosoPizza.Models
{
    public partial class Coupon
    {
        public long Id { get; set; }
        public string Description { get; set; } = null!;
        public DateTime Expiration { get; set; }
    }
}
```
Tip

New scaffolded files can be generated if the database changes. The generated files are overwritten each time, but are created as partial classes you can extend them with custom properties and behaviors in your own, separate files.

Add coupon endpoint

In the Controllers folder, add a file named CouponController.cs containing the following code:

using ContosoPizza.Data;
using ContosoPizza.Models;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;

namespace ContosoPizza.Controllers;

[ApiController]
[Route("[controller]")]
public class CouponController : ControllerBase
{
    PromotionsContext _context;

    public CouponController(PromotionsContext context)
    {
        _context = context;
    }

    [HttpGet]
    public IEnumerable<Coupon> Get()
    {
        return _context.Coupons
            .AsNoTracking()
            .ToList();
    }
}

In the preceding code:

A PromotionsContext is injected into the constructor.
The Get method returns all the coupons.

In Program.cs, replace the // Add the PromotionsContext comment with the following code:
```
builder.Services.AddSqlite<PromotionsContext>("Data Source=./Promotions/Promotions.db");
```
The preceding registers PromotionsContext with the dependency injection system.

Save all your changes and run the app.

dotnet run --urls=https://localhost:5101

Test the endpoint

In another terminal, run the HttpRepl command.
```
httprepl https://localhost:5101
```
Switch to the Coupon endpoint.
```
cd Coupon
```
Retrieve the coupons from the database.
```
get
```
Note expiration is a datetime.

That's it! You've created and modified scaffolding from an existing database!

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