Do you know to use code migrations?

Last updated by Tom Bui [SSW] 3 months ago.See history

Most enterprise applications require a database to store data. Once you have a database you need a way to manage the schema.

Entity Framework Code First Migrations allow you to update a database schema rather than recreate it from scratch. This is useful when you have a production database that you want to keep, but you want to make changes to the schema.

Database Schema Management Options

Managing database schemas effectively is crucial for the smooth operation and evolution of software applications. For more options to manage database schemas, see the best tools for updating database schemas.

Configuring Entity Framework Code First Migrations

The following assumes you have an existing project with a database context, entities, and have already installed the EF Core nuget packages.

  1. Install EF Core Tools

    dotnet new tool-manifest
    dotnet tool install dotnet-ef
  2. Enable migrations

    dotnet ef migrations add InitialCreate

    This will create a migration file in your project. This file contains the code to create the database schema.

    // Example of EF Core Migration in a .NET 8 project
    public partial class AddUserTable : Migration
        protected override void Up(MigrationBuilder migrationBuilder)
                name: "Users",
                columns: table => new
                    Id = table.Column<int>(nullable: false)
                        .Annotation("SqlServer:Identity", "1, 1"),
                    Name = table.Column<string>(nullable: true)
                constraints: table =>
                    table.PrimaryKey("PK_Users", x => x.Id);
        protected override void Down(MigrationBuilder migrationBuilder)
                name: "Users");
  3. Update database

    dotnet ef database update

Using Rider

If you struggle to remember the commands above, Rider has a great UI that makes creating migrations easy. This is especially useful when you have different projects for both startup and migrations.

rider ef core
Rider - EF Core Migrations

Executing Entity Framework Code First Migrations

Once you have some migration, you'll then need to decide when these get run. Naively, developers will often run migrations during program start-up, but this is not recommended. Doing so can cause issues in a web farm environment, as well as cause unnecessary delays during start-up.

var dbContext = scope.ServiceProvider.GetRequiredService<EagleEyeDbContext>();
await dbContext.Database.MigrateAsync();

Figure: Bad example - Running migrations manually during startup in program.cs

Entity Framework Migration Bundles

A place to run migrations is during your CICD deployment pipeline.

dotnet ef migrations bundle --self-contained --force
.\efbundle.exe --connection {$ENVVARWITHCONNECTION}

Figure: Good example - Creating and executing a migration bundle during a CICD pipeline

If an appsettings.json file can be found the connection string can be automatically picked up.

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