configure related entities with the same key - entity-framework

Question

I have an entity type MyEntity that has a primary key string MyEntityCode
I want to make a second entity MyEntityInfo that are extended properties that some MyEntity's are logically associated.
That makes the relationship between these entities one-to-one, with one end optional -- MyEntity logically optionally has a MyEntityInfo, without a navigation property, and MyEntityInfo is required to have a single MyEntity (with a navigation property).
I want to encode this in SQL as MyEntityInfo having a primary key BaseEntityCode that's also a foreign key to MyEntity's MyEntityCode.
How do I configure this encoding in EF6 fluent configuration API.
Sample code
public class MyEntity {
public string MyEntityCode {get; set;}
public int SomeProperty {get; set;}
}
public class MyEntityInfo {
public MyEntity BaseEntity {get; set;}
public string BaseEntityCode {get; set;}
public int OtherInfo {get; set;}
}
public MyEntityConfiguration : EntityConfiguration<MyEntity> {
public MyEntityConfiguration(){
HasKey(e => e.MyEntityCode);
}
}
I thought I could configure MyEntityInfo as
public MyEntityInfoConfiguration : EntityConfiguration<MyEntityInfo> {
public MyEntityInfoConfiguration(){
HasKey(e => e.BaseEntityCode);
HasRequired(e => e.BaseEntity).WithOptional().WithForeignKey(e => BaseEntityCode);
}
}
but WithOptional() doesn't allow chaining to WithForeignKey
Doing the same but with WithMany() so that a foreign key is possible, the multiplicity constraint of one is violated:
Because the Dependent Role refers to the key properties, the upper bound of the multiplicity of the Dependent Role must be '1'.

Answer 1

I thought I could configure MyEntityInfo as
public class MyEntityInfoConfiguration : EntityTypeConfiguration<MyEntityInfo>
{
public MyEntityInfoConfiguration(){
HasKey(e => e.BaseEntityCode);
HasRequired(e => e.BaseEntity).WithOptional().WithForeignKey(e => BaseEntityCode);
}
}
Well, almost, just remove the WithForeignKey call!
public class MyEntityInfoConfiguration : EntityTypeConfiguration<MyEntityInfo>
{
public MyEntityInfoConfiguration()
{
HasKey(e => e.BaseEntityCode);
HasRequired(e => e.BaseEntity).WithOptional();
}
}
Entity Framework 6 has only one implementation of 1:1 associations: the primary key of the dependent entity (here: MyEntityInfo) is the foreign key to the principal entity (here: MyEntity).
There is no WithForeignKey method because with your proposed mapping (without WithForeignKey) EF knows all it needs to know now for the only implementation of 1:1 it has in store.
The produced database model shows the primary key/foreign key dual role of BaseEntityCode:
CREATE TABLE [dbo].[MyEntities] (
[MyEntityCode] [nvarchar](128) NOT NULL,
[SomeProperty] [int] NOT NULL,
CONSTRAINT [PK_dbo.MyEntities] PRIMARY KEY ([MyEntityCode])
)
CREATE TABLE [dbo].[MyEntityInfoes] (
[BaseEntityCode] [nvarchar](128) NOT NULL,
[OtherInfo] [int] NOT NULL,
CONSTRAINT [PK_dbo.MyEntityInfoes] PRIMARY KEY ([BaseEntityCode])
)
...
ALTER TABLE [dbo].[MyEntityInfoes]
ADD CONSTRAINT [FK_dbo.MyEntityInfoes_dbo.MyEntities_BaseEntityCode]
FOREIGN KEY ([BaseEntityCode]) REFERENCES [dbo].[MyEntities] ([MyEntityCode])