Database Migrations in C# (.NET): Entity Framework Migrations

Database Migrations in C# (.NET) with Entity Framework

When developing applications in C# (.NET), one of the key tasks is synchronizing the data model (C# classes) with the database schema. Manually changing tables, columns, and relationships is a time-consuming and error-prone process. The solution to this problem is database migrations, a built-in mechanism of Entity Framework (EF) Core or Entity Framework 6. Migrations allow you to automatically apply changes to the database structure based on code changes while preserving existing data.

What are migrations and why are they needed?

A migration is a set of instructions (C# code) describing how to change the database schema from one version to another. Instead of writing SQL scripts manually, the developer modifies C# models (e.g., adds a new property to a class), and EF generates a migration file. This file is then applied to the database.

• Automation: Eliminates manual SQL writing.
• Versioning: Each migration is a separate file with a timestamp, allowing changes to be rolled back.
• Data safety: When adding a column, EF does not delete existing rows (unless specified otherwise).
• Collaboration: All team members apply the same migrations, preventing schema divergence.

Project Setup

To work with migrations, you need the installed package Microsoft.EntityFrameworkCore.Tools (for EF Core) or EntityFramework (for EF6). Installation via NuGet:

// For EF Core (via Package Manager Console)Install-Package Microsoft.EntityFrameworkCore.Tools

// Or via .NET CLIdotnet add package Microsoft.EntityFrameworkCore.Tools

You will also need a database context inherited from DbContext. Example of a simple model:

public class Blog{    public int Id { get; set; }    public string Title { get; set; }    public string Content { get; set; }}

public class AppDbContext : DbContext{    public DbSet<Blog> Blogs { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)    {        optionsBuilder.UseSqlServer("Server=(localdb)\\\\mssqllocaldb;Database=MyBlogDb;Trusted_Connection=True;");    }}

Creating the First Migration

Open the Package Manager Console (in Visual Studio: View -> Other Windows -> Package Manager Console) or use the .NET CLI. Run the command:

// Via PMCAdd-Migration InitialCreate

// Or via CLIdotnet ef migrations add InitialCreate

After execution, a Migrations folder will appear in the project with two files:

• XXXXXXXXXXXXXX_InitialCreate.cs — the migration class with Up() (what to change) and Down() (how to roll back) methods.
• AppDbContextModelSnapshot.cs — a snapshot of the current model.

Applying the Migration to the Database

To create or update the database to the latest version, run:

// Via PMCUpdate-Database

// Via CLIdotnet ef database update

EF will execute all unapplied migrations in order. If the database does not exist, it will be created automatically.

Adding a New Field and Creating a Migration

Suppose we decide to add a CreatedAt property to the Blog model:

public class Blog{    public int Id { get; set; }    public string Title { get; set; }    public string Content { get; set; }    public DateTime CreatedAt { get; set; } // new field}

Now create a new migration:

Add-Migration