How to map a Value Type which has a reference to an entity?

Question

I'm having a problem with a mapping in Entity Framework.

I have the following classes (simplified):

public class Building
{

    public int ID { get; set; }     
    // *.. snip..* other properties
    public Location Location { get; private set; }
}

public class Location
{
    public string Street {get; set;}
    public Country country {get; set}
}
public class Country
{
    public int ID { get; set; } 
    public string Name { get; set; } 
}

Building and Country are entities, they are saved in the database. Location is a value type and should map to the same table as Building.

However, when I map it this way, entity framework wants to map Location to a table as well and is complaining it has no Key. I don't want to give it a key since it belongs to the Building and should not be an entity at all.

I have seen workarounds which say you need to put Country on the Building-class, but that just doesn't feel good (and is semantically just plain wrong).

I'm using Entity Framework 5

Answer 1

Since the release of Entity Framework Core 2, it is now possible to achieve this using owned entities.

Your configuration would look like:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    // ...
    modelBuilder.Entity<Building>().OwnsOne(x => x.Location);
    modelBuilder.Entity<Location>().HasOne(x => x.Country);
    // ...
}

This way, properties from Location class will be a part of the table Building class is mapped to. This means you will only have tables for Building and Country classes and the Building table will have a foreign key to the Country table.

I know it's been a long since you posted the question, but I thought this answer might be helpful to someone who comes across this question.