实体框架数据库首先是多对多的

Question

I've created an Entity Framework model from the database. I have many-to-many relationship: User - UserRole - Role .

EF created UserRole entity and UserRoles navigation property in the User entity and in Role entity, but I'd rather have Roles in User and Users in Role . Is that possible to be designed through the Model Designer? How can I configure manually many-to-many relationship with a table in the middle?

Answer 1

EF normally creates the intermediate model, if the UserRole table comprises of columns other than foreign keys for User and Role table.

So if you had just 2 columns in the UserRoles table, both FKs to the User and Role tables (not even a surrogate key), EF would create the Model as you wanted. (without any intermediate model) So that is one way to go, for automatic generation of the desired behavior. Have just 2 columns in the table.

But if you have other non-key columns (data) in this table, then what EF is doing is correct. You need the intermediate entity.

And in the case where you don't have any non-key columns, don't want to modify your DB anymore and don't need this middle table in your model, you could manually modify the OnModelCreating, to specify the Many-to-Many and hide the intermediate table.

Here are all the steps:

1. Remove the intermediate table definition C# class from the model layer, and its references in DbContext and User and Role classes.
2. Add a virtual Collection property in both User and Role class, for each other.

eg in the User class,

public virtual ICollection<Role> Roles { get; set; }

and in the User constructor

this.Roles = new HashSet<Role>();

// on the OnModelCreating method, add this snippet
modelBuilder.Entity<User>().HasMany<Role>(u => u.Roles)
                          .WithMany(r => r.Users)
                          .Map(ru => 
                                   {  
                                     ru.MapLeftKey("UserId");        
                                     ru.MapRightKey("RoleId"); 
                                     ru.ToTable("UserRole"); 
                                   });