One-to-One relationship in Entity Framework Core

Question

One-to-One relationship in Entity Framework Core

c# entity-framework entity-framework-core

Question

I have been playing around with .NET Core for the past couple of weeks and decided to try EF Core (coming from ASP.NET MVC with NHibernate). After a bit of digging I found a nice extensions called EF Visual Designer. It allows me to visually create the model and generate code.

I have defined a simple one-to-one relationship shown in the diagram: Simple one-to-one relationship

After generating the code I get the following as Fluent API code:

modelBuilder.Entity<Authentication>()
   .ToTable("Authentications")
   .HasKey(t => t.Id);

modelBuilder.Entity<Authentication>()
    .Property(t => t.Id)
    .IsRequired()
    .ValueGeneratedOnAdd();

modelBuilder.Entity<User>()
     .ToTable("Users")
     .HasKey(t => t.Id);

modelBuilder.Entity<User>()
     .Property(t => t.Id)
     .IsRequired()
     .ValueGeneratedOnAdd();

modelBuilder.Entity<User>()
    .HasOne(x => x.Authentication)
    .WithOne()
    .HasForeignKey("Authentication_Id")
    .IsRequired();

The user class has the following (relevant) properties:

[Key]
[Required]
public Guid Id { get; set; }
...
public virtual Authentication Authentication { get; set; }

Authentication has the following (relevant) property:

[Key]
[Required]
public Guid Id { get; set; }

However when I try to generate a migration I get the following error:

You are configuring a relationship between 'User' and 'Authentication' but have specified a foreign key on 'Authentication_Id'. The foreign key must be defined on a type that is part of the relationship.

I tried switching to a many-to-one relationship and that works without any problems. That could be a work-around but not a very clean one. Is this perhaps due to naming issues like both entities having "Id" as primary key?

If that's the case, what is the "best practice"? Do I give every entity a unique ID-column name? How do I go about an abstract entity with derived classes all inheriting the ID column?

Roel

Popular Answer

You need to put the foreign key on the other class. It looks like you don't have a property "Authentication_Id" on the Authentication class.

D.R.

View more on Stack Overflow

David Liang · Accepted Answer · 8/21/2019 6:08:40 PM

I have never used EF Visual Designer to generate codes but just by looking at your code, either the User entity needs the foreign key of Authentication, or Authentication entity needs the foreign key of User.

Let's say you want to put the foreign key in User:

public class User
{
    [Key]
    [Required]
    public Guid Id { get; set; }

    public Guid AuthenticationId { get; set; }

    // Even this navigation property is optional
    // for configuring one-to-one relationship
    public virtual Authentication Authentication { get; set; }
}

public Authentication
{
    [Key]
    [Required]
    public Guid Id { get; set; }
}

Then the one-to-one relationship should be configured as:

modelBuilder.Entity<User>()
    .HasOne(x => x.Authentication)

    // Or like this if you don't have Authentication navigation property:
    //.HasOne<Authentication>()

    .WithOne()
    .HasForeignKey(x => x.AuthenticationId);

And no, you don't have to give every entity a unique ID-column name. In fact, you can call whatever in your code and rename it inside the configuration:

modelBuilder.Entity<User>()
    .Property(x => x.Id).HasColumnName("WHATEVER_YOU_WANT_TO_CALL_IN_DB");

One-to-One relationship in Entity Framework Core

Question

Fastest Entity Framework Extensions

Accepted Answer

Popular Answer

Performance

Expression Evaluator

Related