c# - EF Code First - WithMany()

Question

I recently came by the class ManyNavigationPropertyConfiguration<TEntity, TTarget> , and within that class there I found a method named WithMany() with 2 overloads.

The first overload: WithMany()

Configures the relationship to be many:many without a navigation property on the other side of the relationship.

The second overload: WithMany(Expression<Func<TTarget, ICollection<TEntity>>>)

Configures the relationship to be many:many with a navigation property on the other side of the relationship.

Now is my question, why would you configure a relationship to be many:many without a navigation property (the first overload)? I dont see any scenarios where that would be helpful... Any thoughts?

Answer 1

An example might be this model:

public class User
{
    public int UserId { get; set; }
    public string Name { get; set; }
    public ICollection<Role> Roles { get; set; }
}

public class Role
{
    public int RoleId { get; set; }
    public string Description { get; set; }
}

If you are never interested to retrieve all users which are in a specific role, adding a navigation property ...

public ICollection<User> Users { get; set; }

... to the Role class would be unnecessary overhead.

But you still must EF tell that a many-to-many relationship between User and Role exists ...

modelBuilder.Entity<User>()
            .HasMany(u => u.Roles)
            .WithMany();

... because the default convention mappings would create a wrong relationship, namely a one-to-many relationship, corresponding to this mapping:

modelBuilder.Entity<User>()
            .HasMany(u => u.Roles)
            .WithOptional();