One-To-One relationship with the same Entity Framework table

Question

I don’t know how to perform the relationship one to one on the same table on Entity Framework.

Example:

namespace cruddef.Models
{
    public class Document
    {
        public int DocumentID { get; set; }
        public int SourceDocumentID { get; set; }
    }  
}

What I need to do, I need to relate the table Document with itself, using the key SourceDocumentID with the DocumentID, This in the configuration document of EF and I need this to work:

public virtual Document DOCUMENT_SOURCE { get; set; }

Answer 1

There’s a way this works out that’s a self relationship 1 for 1, I don’t know what your real goal is to do so, maybe there are better ways, but, I ended up doing a minimal example and it works, because, in the relations of Entity Framework there is always the list navigation and in that case there is no (list example).

Remarks:

• for this to work in the item that will be the foreign key of the table must be of the type null.
• configure this foreign key field with [ForeignKey("DOCUMENT_SOURCE")] of namespace System.ComponentModel.DataAnnotations.Schema right now is configuring self - relationship.

• minimal example:

  namespace cruddef.Models
  {
      public class Document
      {
          public int DocumentID { get; set; }
  
          [ForeignKey("DOCUMENT_SOURCE")]
          public int? SourceDocumentID { get; set; }
          public virtual Document DOCUMENT_SOURCE { get; set; }
      }  
  }
  

---

In the example created by me it was like this:

namespace CslAppEFAutoOneToOne.Models
{
   public class Document
   {
      public int DocumentId { get; set; }
      public string Title { get; set; }

      [ForeignKey("SourceDocument")]
      public int? SourceDocumentId { get; set; }
      public virtual Document SourceDocument { get; set; }
   }

   public class DatabaseContext : DbContext
   {
      public DatabaseContext()
         : base("Server=.\\SqlExpress;Database=TestOneToOne;User Id=sa;Password=senha;")
      {
         Database.SetInitializer<DatabaseContext>(null);
      }

      public DbSet<Document> Document { get; set; }    
   }
}

Using:

using (DatabaseContext db = new DatabaseContext())
{
    Document d1 = new Document()
    {
       Title = "Document 1"
    };

    Document d2 = new Document()
    {
       SourceDocumentId = d1.DocumentId,
       SourceDocument = d1,
       Title = "Document 2"
    };
    db.Document.Add(d1); //inserindo documento 1
    db.Document.Add(d2); //inserindo documento 2 relacionado com 1
    db.SaveChanges(); // salvando 

    var doc1 = db.Document.AsNoTracking()
       .Include("SourceDocument")
       .Where(x => x.DocumentId == 2)
       .FirstOrDefault(); // filtro e seleção da relação.
}

In this example of how to use a record was inserted and the other related to the first and research seeking this relationship.