I have two classes. How can I turn these two classes into a one to one relationship using the entity framework code first method?
public class Region
{
public int RegionId { get; set; }
public string Name { get; set; }
public virtual Factory _factory { get; set; }
}
public class Factory
{
public int FactoryId { get; set; }
public string Name { get; set; }
public virtual Region _region { get; set; }
}
When I try this, I get this error:
Multiplicity is not valid in Role 'Region_Factory_Source' in relationship 'Region_Factory'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be '*'.
Best Answer
This occurs in CodeFirst because of the virtual keyword. In effect, you are creating a relationship where creating one item requires the creation of the other. however, the virtual keyword allows lazy instantiation, which means that creating an object of one type doesn't automatically create the other type, allowing the Id on the foreign item to be null. This implies a 0..1 relationship, but since each side is virtual, what you get is a 0..0 which isn't allowed.
There are 2 methods which you can use to remedy the situation.
Region
add a property forFactoryId
and onFactory
add a property forRegionId
There are other ways to help Entity Framework determine which object is the Dependent Object, i.e. using Entity Framework Fluent api.
from MSDN
the following code would create a Principal
Factory
with a DependentRegion