Interview Question

How can you seed a database with initial data in Entity Framework Core?

Answer

EF Core provides several approaches to seed database data. Here are the main methods:

1. Using Model Builder

public class ApplicationDbContext : DbContext
{
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Category>().HasData(
            new Category { Id = 1, Name = "Electronics" },
            new Category { Id = 2, Name = "Books" }
        );
    }
}

2. Using Migrations

public partial class SeedData : Migration
{
    protected override void Up(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.InsertData(
            table: "Categories",
            columns: new[] { "Id", "Name" },
            values: new object[] { 1, "Electronics" }
        );
    }

    protected override void Down(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.DeleteData(
            table: "Categories",
            keyColumn: "Id",
            keyValue: 1
        );
    }
}

3. Using Extension Method

public static class DbInitializer
{
    public static void Initialize(ApplicationDbContext context)
    {
        if (!context.Categories.Any())
        {
            var categories = new[]
            {
                new Category { Name = "Electronics" },
                new Category { Name = "Books" }
            };
            
            context.Categories.AddRange(categories);
            context.SaveChanges();
        }
    }
}

// In Program.cs
using (var scope = app.Services.CreateScope())
{
    var context = scope.ServiceProvider.GetRequiredService<ApplicationDbContext>();
    DbInitializer.Initialize(context);
}

Key Points 💡

• ModelBuilder.HasData is best for reference data
• Migrations are good for version-controlled data
• Extension methods are flexible for development data
• Always handle existing data scenarios

Common Follow-up Questions

1. How do you handle seeding data in production vs development?
2. How can you seed related entities maintaining referential integrity?
3. What’s the best practice for seeding large amounts of data?