Code-first foreign key references primary key in same table EF Core 7

Question

I have this class with 2 fields, one serves as the primary key, and the other is a foreign key:

public partial class CCSSubCuenta
{
    [Key]
    [Required]
    [MaxLength(6)]
    [Column("SCTA_CLAVE", TypeName = "decimal(6)")]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public decimal SctaClave { get; set; }

    [MaxLength(6)]
    [Column("SCTA_CLAVE_SCTA_MAESTRA", TypeName = "decimal(6)")]
    public decimal? SctaClaveSctaMaestra { get; set; }
}

I'm trying to use the [ForeignKey("SCTA_CLAVE")] for referencing the primary key, but it is not working when I deploy my migrations.

What is the correct way to define the foreign key via data annotations or Fluent API?

Answer 1

You can't use [ForeignKey] on a foreign key property.

[ForeignKey] is to decorate a navigation property to indicate the foreign key column :

public class File
{
    public int Id { get; set; }
    public string Name { get; set; }
    [ForeignKey("FolderId")]
    public Folder? Folder { get; set; } // Navigation Property
}

Or the foreign key property :

public class File
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int FolderId { get; set; } // Foreign Key Property
    [ForeignKey(nameof(FolderId))]
    public Folder? Folder { get; set; } // Navigation Property
}

It can also decorate a collection navigation property, but it's a other subject.

---

In EF Core, it's the navigation property that define relation. But your model don't have navigation property.

You need to define the relation with a navigation property like :

public partial class CCSSubCuenta
{
    [Key]
    ...
    public decimal SctaClave { get; set; }

    [MaxLength(6)]
    [Column("SCTA_CLAVE_SCTA_MAESTRA", TypeName = "decimal(6)")]
    public decimal? SctaClaveSctaMaestra { get; set; }

    [ForeignKey(nameof(SctaClaveSctaMaestra))]
    public CCSSubCuenta? SctaClaveSctaMaestraNav { get; set; }
}

If you don't want modify the model, you can add a shadow navigation property with the fluent syntax :

public class CuentaContext : DbContext
{
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.Entity<CCSSubCuenta>()
            .HasOne<CCSSubCuenta>()
            .WithMany()
            .HasForeignKey(c => c.SctaClaveSctaMaestra);
    }
}