如何从其他类继承DbSet？拆分DbContext后无法生成表

Hey there! Let's work through this issue you're having. When splitting DbSets into smaller classes but not seeing corresponding tables generated or visible in your ApplicationDbContext, the root problem is almost always that EF Core isn't recognizing those split classes as part of your context's model. Here's how to fix it:

1. Use Partial Classes (Simplest & Most Reliable Approach) #

The cleanest way to split DbSets across files is to make your ApplicationDbContext a partial class. EF Core automatically merges all partial class definitions, so it will pick up DbSets from every file.

Example structure:

// ApplicationDbContext.cs (base file)
public partial class ApplicationDbContext : DbContext
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) 
        : base(options) { }
}

// ApplicationDbContext.Products.cs (product-related DbSets)
public partial class ApplicationDbContext
{
    public DbSet<Product> Products { get; set; }
    public DbSet<ProductCategory> ProductCategories { get; set; }
}

// ApplicationDbContext.Orders.cs (order-related DbSets)
public partial class ApplicationDbContext
{
    public DbSet<Order> Orders { get; set; }
    public DbSet<OrderItem> OrderItems { get; set; }
}

With this setup, EF Core treats all these DbSets as part of the same ApplicationDbContext—no extra configuration needed.

2. Explicitly Register Entities (If Partial Classes Aren't Your Style) #

If you prefer keeping DbSets in separate standalone classes, you need to tell EF Core about each entity type. Here are two ways to do this:

Option A: Use ModelBuilder Extensions #

Create extension methods to group entity registrations, then call them in OnModelCreating:

// DbSetRegistrationExtensions.cs
public static class DbSetRegistrationExtensions
{
    public static void AddProductEntities(this ModelBuilder builder)
    {
        builder.Entity<Product>();
        builder.Entity<ProductCategory>();
    }

    public static void AddOrderEntities(this ModelBuilder builder)
    {
        builder.Entity<Order>();
        builder.Entity<OrderItem>();
    }
}

// In your ApplicationDbContext
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);
    modelBuilder.AddProductEntities();
    modelBuilder.AddOrderEntities();
}

Option B: Use DbSet Holder Classes #

If you want to keep DbSet properties in separate classes, you still need to register each entity explicitly:

// ProductDbSets.cs
public class ProductDbSets
{
    public DbSet<Product> Products { get; set; }
    public DbSet<ProductCategory> ProductCategories { get; set; }
}

// ApplicationDbContext.cs
public class ApplicationDbContext : DbContext
{
    public ProductDbSets ProductSets { get; set; }
    public OrderDbSets OrderSets { get; set; }

    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) 
        : base(options) { }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        // Explicitly register every entity in your holder classes
        modelBuilder.Entity<Product>();
        modelBuilder.Entity<ProductCategory>();
        modelBuilder.Entity<Order>();
        modelBuilder.Entity<OrderItem>();
    }
}

3. Verify EF Core Recognizes Your Entities #

To confirm your entities are being picked up, add a quick check during app startup:

using (var scope = app.Services.CreateScope())
{
    var dbContext = scope.ServiceProvider.GetRequiredService<ApplicationDbContext>();
    var entityTypes = dbContext.Model.GetEntityTypes();
    
    Console.WriteLine("Registered entities:");
    foreach (var type in entityTypes)
    {
        Console.WriteLine($"- {type.ClrType.Name}");
    }
}

If your entities don't show up here, EF Core isn't aware of them—double-check your registration setup.

4. Update Migrations & Database #

Once your entities are recognized, make sure to generate a new migration and apply it:

# Package Manager Console
Add-Migration AddSplitDbSets
Update-Database

# CLI
dotnet ef migrations add AddSplitDbSets
dotnet ef database update

Open the generated migration file to confirm it includes create statements for all your split entities.

内容的提问来源于stack exchange，提问作者L. Piotrowski