实体框架中没有外键的一对多关系？

Question

The title may be misleading, but right now I can't seem to formulate the right words for what I'm searching for.

As it stands, Entity A has many Entity B, but Entity B will not include an Entity A foreign key.

How does that work?

At first, I thought to use the following property in my model.

public virtual ICollection<B> Bs { get; set; }

But that's if B has a foreign key to A. Suggestions? or is this not a thing? Must I create a separate model just to relate A and B if B does not have the foreign key?

Answer 1

I don't know why there can't be an FK on entity B to entity A, but without any sort of referential constraints, there can be no traversal between the two entities (ie you can't extract all B's per given A, and you can't extract the A for a given B). The easiest way I can tell you is to just add that FK, but if it's not possible, you would need to create another entity that simply acts as the proxy/map for your entity B. BProxy entities should have a 1-1 relationship with B entities.

public class BProxy 
{
     [Key]
     public int Id {get; set;}
     [Required]
     public int EntityBId {get; set;}
     public virtual EntityB {get; set;}
     [Required]
     public int EntityAId {get; set;}
     public virtual EntityA {get; set;}
}

Your Entity A would then have a collection of BProxy objects instead of B objects

public virtual ICollection<BProxy> BProxies { get; set; }

This way, you can create queries that traverse the relationships both ways through LINQ.