Database migrations in Entity Framework Core (EF Core) are a way to update the database schema in a controlled and incremental manner. They are particularly useful for evolving the database schema over time as your application evolves. Here’s a step-by-step guide on how to perform database migrations using EF Core in ASP.NET 8.
1. Setup and Configuration
Before you can perform migrations, you need to set up Entity Framework Core in your ASP.NET 8 application. Here’s how you can do that:
1.1. Install EF Core Packages
You need to install the Entity Framework Core packages. You can do this via NuGet Package Manager or the CLI.
Using NuGet Package Manager Console:
bash
Install-Package Microsoft.EntityFrameworkCore
Install-Package Microsoft.EntityFrameworkCore.Design
Install-Package Microsoft.EntityFrameworkCore.SqlServer # Or any other database provider
Using .NET CLI:
bash
dotnet add package Microsoft.EntityFrameworkCore
dotnet add package Microsoft.EntityFrameworkCore.Design
dotnet add package Microsoft.EntityFrameworkCore.SqlServer # Or any other database provider
1.2. Configure DbContext
Define a DbContext class and configure it in Program.cs (or Startup.cs for older ASP.NET Core versions).
Example: MyDbContext.cs
csharp
using Microsoft.EntityFrameworkCore;
public class MyDbContext : DbContext
{
public DbSet<Product> Products { get; set; }
public DbSet<Category> Categories { get; set; }
public MyDbContext(DbContextOptions<MyDbContext> options)
: base(options)
{
}
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
// Fluent API configurations (if any) go here
}
}
Example: Configure DbContext in Program.cs
csharp
var builder = WebApplication.CreateBuilder(args);
// Configure DbContext with SQL Server (or another provider)
builder.Services.AddDbContext<MyDbContext>(options =>
options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection")));
var app = builder.Build();
1.3. Add Connection String
Add the connection string to appsettings.json.
Example: appsettings.json
json
{
"ConnectionStrings": {
"DefaultConnection": "Server=myServerAddress;Database=myDataBase;User Id=myUsername;Password=myPassword;"
}
}
2. Creating and Applying Migrations
Once EF Core is set up, you can create and apply migrations.
2.1. Add a Migration
A migration represents a set of changes to the database schema.
Using .NET CLI:
bashdotnet ef migrations add InitialCreate
Using Package Manager Console:
bashAdd-Migration InitialCreate
InitialCreate: The name of the migration. You can choose any descriptive name.
This command generates a migration file in the Migrations folder. The file contains code to apply and revert the changes made to the database schema.
2.2. Apply the Migration
To apply the migration and update the database schema:
Using .NET CLI:
bashdotnet ef database update
Using Package Manager Console:
bashUpdate-Database
This command updates the database schema based on the migration files.
3. Managing Migrations
3.1. Viewing Pending Migrations
You can view the list of pending migrations that have not yet been applied to the database.
Using .NET CLI:
bashdotnet ef migrations list
Using Package Manager Console:
bashGet-Migrations
3.2. Removing the Last Migration
If you need to remove the last migration (e.g., if it was created by mistake), you can do so:
Using .NET CLI:
bashdotnet ef migrations remove
Using Package Manager Console:
bashRemove-Migration
- This will remove the last migration file but will not affect the database.
4. Handling Data Changes
When you make changes to your models, such as adding a new property or changing a relationship, you need to create a new migration to apply these changes to the database.
Update Models: Modify your entity classes and/or
DbContext.Create a Migration: Add a new migration to capture the changes.
bashdotnet ef migrations add AddedNewPropertyApply the Migration: Update the database with the new migration.
bashdotnet ef database update
5. Customizing Migrations
Sometimes, you might need to customize the migration code. You can manually edit the migration files generated in the Migrations folder.
Example: Adding a custom migration script
csharp
public partial class AddedNewProperty : Migration
{
protected override void Up(MigrationBuilder migrationBuilder)
{
migrationBuilder.AddColumn<string>(
name: "NewProperty",
table: "Products",
type: "nvarchar(max)",
nullable: true);
}
protected override void Down(MigrationBuilder migrationBuilder)
{
migrationBuilder.DropColumn(
name: "NewProperty",
table: "Products");
}
}
UpMethod: Contains the code to apply changes to the database schema.DownMethod: Contains the code to revert changes if the migration is rolled back.
6. Seeding Data
You can seed initial data into your database using migrations.
Example: Seeding Data in OnModelCreating
csharp
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Product>().HasData(
new Product { Id = 1, Name = "Sample Product", Price = 19.99M }
);
}
To apply seeded data, create a migration after adding the seeding code and apply it.
7. Migrating to a New Database
If you need to initialize a new database with the current schema and data, use:
Using .NET CLI:
bashdotnet ef database update
This will apply all migrations to the new database.
Summary
- Setup EF Core: Install necessary packages and configure
DbContext. - Create Migrations: Use
dotnet ef migrations addorAdd-Migrationto create migration files. - Apply Migrations: Use
dotnet ef database updateorUpdate-Databaseto update the database. - Manage Migrations: View, remove, and customize migrations as needed.
- Handle Data Changes: Create new migrations for model changes and apply them.
- Seed Data: Initialize the database with default data using seeding.
By following these steps, you can effectively manage your database schema changes and keep your database in sync with your application’s data model.