One to one optional relationship using Entity Framework Fluent API
We want to use one to one optional relationship using Entity Framework Code First. We have two entities.
public class PIIUser
{
public int Id { get; set; }
public int? LoyaltyUserDetailId { get; set; }
public LoyaltyUserDetail LoyaltyUserDetail { get; set; }
}
public class LoyaltyUserDetail
{
public int Id { get; set; }
public double? AvailablePoints { get; set; }
public int PIIUserId { get; set; }
public PIIUser PIIUser { get; set; }
}
PIIUser may have a LoyaltyUserDetail but LoyaltyUserDetail must have a PIIUser . We tried these fluent approach techniques.
modelBuilder.Entity<PIIUser>()
.HasOptional(t => t.LoyaltyUserDetail)
.WithOptionalPrincipal(t => t.PIIUser)
.WillCascadeOnDelete(true);
This approach didn't create LoyaltyUserDetailId foreign key in PIIUsers table.
After that we tried the following code.
modelBuilder.Entity<LoyaltyUserDetail>()
.HasRequired(t => t.PIIUser)
.WithRequiredDependent(t => t.LoyaltyUserDetail);
But this time EF didn't create any foreign keys in these 2 tables.
Do you have any ideas for this issue? How can we create one to one optional relationship using entity framework fluent api?
EF Code First supports 1:1 and 1:0..1 relationships. The latter is what you are looking for ("one to zero-or-one").
Your attempts at fluent are saying required on both ends in one case and optional on both ends in the other.
What you need is optional on one end and required on the other.
Here's an example from the Programming EF Code First book
modelBuilder.Entity<PersonPhoto>()
.HasRequired(p => p.PhotoOf)
.WithOptional(p => p.Photo);
The PersonPhoto entity has a navigation property called PhotoOf that points to a Person type. The Person type has a navigation property called Photo that points to the PersonPhoto type.
In the two related classes, you use each type's primary key, not foreign keys. ie, you won't use the LoyaltyUserDetailId or PIIUserId properties. Instead, the relationship depends on the Id fields of both types.
If you are using the fluent API as above, you do not need to specify LoyaltyUser.Id as a foreign key, EF will figure it out.
So without having your code to test myself (I hate doing this from my head)... I would translate this into your code as
public class PIIUser
{
public int Id { get; set; }
public LoyaltyUserDetail LoyaltyUserDetail { get; set; }
}
public class LoyaltyUserDetail
{
public int Id { get; set; }
public double? AvailablePoints { get; set; }
public PIIUser PIIUser { get; set; }
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<LoyaltyUserDetail>()
.HasRequired(lu => lu.PIIUser )
.WithOptional(pi => pi.LoyaltyUserDetail );
}
That's saying LoyaltyUserDetails PIIUser property is required and PIIUser's LoyaltyUserDetail property is optional.
You could start from the other end:
modelBuilder.Entity<PIIUser>()
.HasOptional(pi => pi.LoyaltyUserDetail)
.WithRequired(lu => lu.PIIUser);
which now says PIIUser's LoyaltyUserDetail property is optional and LoyaltyUser's PIIUser property is required.
You always have to use the pattern HAS/WITH.
HTH and FWIW, one to one (or one to zero/one) relationships are one of the most confusing relationships to configure in code first so you are not alone! :)
Just do like if you have one-to-many relationship between LoyaltyUserDetail and PIIUser so you mapping should be
modelBuilder.Entity<LoyaltyUserDetail>()
.HasRequired(m => m.PIIUser )
.WithMany()
.HasForeignKey(c => c.LoyaltyUserDetailId);
EF should create all foreign key you need and just don't care about WithMany !
There are several things wrong with your code.
A 1:1 relationship is either: PK<-PK , where one PK side is also an FK, or PK<-FK+UC , where the FK side is a non-PK and has a UC. Your code shows you have FK<-FK , as you define both sides to have an FK but that's wrong. I recon PIIUser is the PK side and LoyaltyUserDetail is the FK side. This means PIIUser doesn't have an FK field, but LoyaltyUserDetail does.
If the 1:1 relationship is optional, the FK side has to have at least 1 nullable field.
pswg above did answer your question but made a mistake that s/he also defined an FK in PIIUser, which is of course wrong as I described above. So define the nullable FK field in LoyaltyUserDetail , define the attribute in LoyaltyUserDetail to mark it the FK field, but don't specify an FK field in PIIUser .
You get the exception you describe above below pswg's post, because no side is the PK side (principle end).
EF isn't very good at 1:1's as it's not able to handle unique constraints. I'm no expert on Code first, so I don't know whether it is able to create a UC or not.
(edit) btw: A 1:1 B (FK) means there's just 1 FK constraint created, on B's target pointing to A's PK, not 2.
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