Child is used by different parents in one to one relation

Question

Assuming I have a child

public class Child
{
    public int Id {get; set;}
}

and two parents which using the childs in one to one relations. One child should be used only at one parent. But I want to use the child with Id=1 at ParentA and the child with Id=2 at ParentB for example.

public class ParentA
{
    public int Id {get; set;}
    public int ChildId {get; set;}
    public Child Child {get; set;}
}

public class ParentB
{
    public int Id {get; set;}
    public int ChildId {get; set;}
    public Child Child {get; set;}
}

I want the navigation property at the parents if possible.

I know how to configure a one to one relation when having only one parent because then I would have to add a navigation property in the Child class and would add the configuration in the OnModelCreating method of my DbContext implementation.

But for the scenario with 2+ parents I don't know how the configuration in OnModelCreating should look like.

Answer 1

Based on the additional info from the comments that the ParentA and ParentB are not mapped to the same table you could implement 2 one-to-one relationships resulting in:

public class Child
{
    public int Id {get; set;}
    public ParentA A {get; set;}
    public ParentB B {get; set;}
}

This would mean that when A is initialized B is null and vice versa.

Alternatively if ParentA and ParentB are similar enough and it makes sence to have a common inheritance:

public class Child
{
    public int Id {get; set;}
    public Parent {get; set;}
}

public class Parent
{
    public int Id {get; set;}
    public int ChildId {get; set;}
    public Child Child {get; set;}
}

public class ParentA : Parent { }

public class ParentB : Parent { }

And have the one-to-one relationship mapped between Parent and Child

This might also require DB changes.