实体框架：处理两个实体之间的多个关系

Question

There are two entities:

1. Group
2. Yuvak - Person

"Other" person is designed in back-end who has no group. (null)

A Yuvak - Person will always have one HomeGroup. (1=>1) And will have no groups to control.

A Nirikshak(Head) - Person will always have one HomeGroup. (1=>1) But he will also have multiple groups to control - GroupsOfNirikshak. (1=>Many)

A Group will have multiple Yuvaks (1=>Many)

and all groups mostly will have only one Head. (Initially a new group might not have any head but zero or more yuvaks-persons.)

[Table("Group")]
public class Group
{
    [Key]
    public int Id { get; set; }
    .....       
    public virtual List<Yuvak> Yuvaks { get; set; }
    [ForeignKey("Nirikshak")]
    public int? NirikshakId { get; set; }
    public virtual Yuvak Nirikshak { get; set; }
}

[Table("Yuvak")]
public class Yuvak
{
    [Key]
    public int Id { get; set; }
    .....
    [ForeignKey("HomeGroup")]
    public int? HomeGroupId { get; set; }
    public virtual Group HomeGroup { get; set; }
    public virtual List<Group> GroupsOfNirikshak { get; set; }
}

I already has provided two foreign keys for 1=>1 relationships (nullable) in both entities. And now to manage many to many relationship it should automatically create a third table with "Yuvak_Id" and "Group_Id" columns if they are not null. But as here the FKs are null; instead of creating a third table it adds a foreign key column in both the tables.(Group:"Yuvak_Id" and Yuvak:"Group_Id")

What should I do so that to maintain Yuvak-HomeGroup it should use above provided foreign keys only and for many to many relationship (Head-GroupsOfNirikshak & Group-Yuvaks )it should create a seperate table.

Can I create a separate table for many to many relationship like : (ID,YuvakID,GroupID) How can I do that?

I tried to do that but got different errors like below :

1. The navigation property 'HomeGroup' declared on type 'YTKGoshthiManagment.Models.Yuvak' has been configured with conflicting foreign keys.
2. Multiplicity is not valid in Role 'Yuvak_HomeGroup_Target' in relationship 'Yuvak_HomeGroup'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be '*'.

.....

and so on.

Answer 1

Use the "Fluent Api" !

In your context class write (for example) :

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
     modelBuilder.Entity<Group>()
                 .HasOptional(t => t.Nirikshak)
                 .WithMany(t => t.GroupsOfNirikshak)
                 .HasForeignKey(t => t.NirikshakId);
}

Answer 2

You can remove the annotations on the classes and properties. Once you have a Model-based Class on another, Entity Framework will automatically create a foreign key relationship on it. It will process Yuvak as a node on the Group Graph object. You need not declare the annotations since EF will do that for you automatically.