使用ModelBuilder在EFCore5中播种多对多数据库吗? [英] Seeding many-to-many databases in EFCore5 with ModelBuilder?

问题描述

有

There are many questions about seeding many-to-many relationships in Entity Framework. However, most of them are extremely old, and many-to-many behavior has changed significantly in EFCore5. The official docs recommend overriding OnModelCreating to implement ModelBuilder.Entity<>.HasData().

However, with the new many-to-many behavior (without explicit mappings), I can find no clear path to seed the intermediate tables. To use the example of this tutorial, the BookCategories class is now implicit. Therefore, there is no path to explicitly declare the intermediate table values while seeding.

I've also tried simply assigning the arrays, e.g.,:

public class Book
{
    public int BookId { get; set; }
    public string Title { get; set; }
    public ICollection<Category> Categories { get; set; }
}  
public class Category
{
    public int CategoryId { get; set; }
    public string CategoryName { get; set; }
    public ICollection<Book> Books { get; set; }
}  

And then at seed time:

Book book = new Book() { BookId = 1, Title = "Brave New World" }

Category category = new Category() { CategoryId = 1, CategoryName = "Dystopian" }

category.Books = new List<Book>() { book };
book.Categories = new List<Category>() { category };

modelBuilder.Entity<Book>().HasData(book);
modelBuilder.Entity<Category>().HasData(category);

... but there are no entries created for BookCategories in the resulting migration. This was somewhat expected, as this article suggests that one must explicitly seed the intermediate table. What I want is something like this:

modelBuilder.Entity<BookCategory>().HasData(
  new BookCategory() { BookId = 1, CategoryId = 1 }
);

However, again, since there is no concrete class to describe BookCategories in EFCore5, the only way I can think of to seed the table is to manually edit the migration with additional MigrationBuilder.InsertData commands, which rather defeats the purpose of seeding data via application code.

解决方案

Update (EF Core 5.0.2)

It's working well using the name of the associative table:

    builder.Entity("ContractDeclarationType").HasData(
        new { ContractsId = 1L, DeclarationTypesId = 1L },
        new { ContractsId = 1L, DeclarationTypesId = 2L },
        new { ContractsId = 1L, DeclarationTypesId = 3L });

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