How to configure many to many relationship using entity framework fluent API

问题

I'm trying to set up a many to many relationship in EF code first but the default conventions is getting it wrong. The following classes describes the relationship:

class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
}

class Account
{        
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Product> Products { get; set; }
}

One Account can have many Products.

However the EF conventions will create the DB tables as:

Products Table
--------------
Id
Name
Account_Id  <- What is this?

Accounts Table
--------------
Id
Name

This doesn't look like a many-to-many table structure? How can i get configure the fluent API to reflect the relationship and create an intermediary table:

AccountProducts Table
---------------------
Account_Id
Product_Id

回答1:

modelBuilder.Entity<Account>()
            .HasMany(a => a.Products)
            .WithMany()
            .Map(x =>
            {
                x.MapLeftKey("Account_Id");
                x.MapRightKey("Product_Id");
                x.ToTable("AccountProducts");
            });

回答2:

What EF has suggested is a one-to-many relationship.

One Account can have many Products, i.e. each Product has an Account_Id

If you want a many to many relationship (and create an intermediary table), the following should work

class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Account> Accounts { get; set; }
}

class Account
{        
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Product> Products { get; set; }
}

回答3:

Code first is creating tables in right relational way. When

One Account can have many Products.

Products table should store key for its Account, as it actually does now.

What you are trying to see in db, is many-to-many relationship, not one to many. If you want to achieve that with code first, you should redesign your entities

class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Account> Accounts { get; set; }
}

class Account
{        
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Product> Products { get; set; }
}

In this case, one product can have many accounts, and one account can have many products.

回答4:

        public AccountProductsMap()
    {
        this.ToTable("AccountProducts");
        this.HasKey(cr => cr.Id);

        this.HasMany(cr => cr.Account)
            .WithMany(c => c.Products)
            .Map(m => m.ToTable("AccountProducts_Mapping"));
    }

来源：https://stackoverflow.com/questions/8927278/how-to-configure-many-to-many-relationship-using-entity-framework-fluent-api