Mapping for one to one with nullable value

Question

I have two entity classes, Contact and User.

The User has ContactID as foreign key to Contact. I can show relation of the User to Contact.

Now i also need Contact to User relation with the same foreign key in User table (not in Contact)

public class Contact{
   public int ContactID {get;set;}
   // This relation doesn't work
   // Need to Make this Work
   public User ContactUser {get;set;}
}

public class User {
   public string Id {get;set;}
   public int? ContactID {get;set;}
   // This Relation works
   [ForeignKey("ContactID")]
   public Contact Contact {get;set;}
}

So i need to make the ContactUser relation work on Contact. What kind of mapping should i use?

Edit

As suggested I used : modelBuilder.Entity<Contact>().HasRequired(c => c.ContactUser).WithOptional(pi => pi.Contact); I removed ForeignKey attribute from User, it as causing Multiplicity...error

But i get error Like: Invalid column name 'User_Id'.

score 0 · Accepted Answer · edited May 23 '17 at 11:58

What you are looking for is a

One to Zero-or-One Mapping

There is a great anwser here on StackOverflow.

In your Case explicit is following required:

modelBuilder needs the WithOptional-Methode

.WithOptional(pi => pi.Contact);
no Property for the ContactID

Example for EF 6.0

public class Contact
{
    [Key]
    public int ContactId { get; set; }

    public string ContactName { get; set; }
    public User ContactUser { get; set; }
}

public class User
{
    [Key]
    public int UserId { get; set; }

    public string UserName { get; set; }
    public Contact Contact { get; set; }
}

In the DbContext-Class:

public class CodeFirstContext : DbContext
{
    public CodeFirstContext()
    {
        Database.SetInitializer(new DropCreateDatabaseIfModelChanges<CodeFirstContext>());            
    }

    public DbSet<Contact> Contacts { get; set; }
    public DbSet<User> Users { get; set; }


    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<User>()
          .HasRequired(co => co.Contact)
          .WithOptional(cu => cu.ContactUser);

        base.OnModelCreating(modelBuilder);
    }
}

In this Case now says User's Contact property is optional and Contact's User property is required. I hope this is the right constellation for your project.

Console Test

class Program
{
    static void Main(string[] args)
    {
        using (var db = new CodeFirstContext())
        {
            Console.Write("Enter a name: ");
            var name = Console.ReadLine();

            var cont = new Contact { ContactName = name };
            db.Contacts.Add(cont);
            db.SaveChanges();

            var usr = new User { UserName = "MyUsername", Contact = cont };
            db.Users.Add(usr);
            db.SaveChanges();

            var query = from b in db.Contacts
                        orderby b.ContactName
                        select b;

            Console.WriteLine("All contacts in the database:");
            foreach (var item in query)
            {
                Console.WriteLine(item.ContactName);
            }

            Console.WriteLine("Press any key to exit...");
            Console.ReadKey();
        }
    }
}

I am getting error: Invalid column name 'User_Id'. Mapping Used : `modelBuilder.Entity().HasRequired(c => c.ContactUser).WithOptional(pi => pi.Contact);` — Ruchan, Apr 20 '15 at 11:35
Got a working Solution here: http://1drv.ms/1yKLZuR - The Problem roots in the [Key]-Attribute. — Smartis has left SO again, Apr 20 '15 at 13:23
This still didn't work for me, must have got something wrong with my other mappings. I solved it for now with a different method without mapping. Thanks for your help. — Ruchan, May 07 '15 at 08:11

score 0 · Answer 2 · answered Apr 20 '15 at 13:28

0

Try this:

public class Contact
{
    [Key, DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int ContactId { get; set; }

    public string ContactName { get; set; }
    [ForeignKey("ContactId")]
    public User ContactUser { get; set; }
}

answered Apr 20 '15 at 13:28

Martin Vich

1,062
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Mapping for one to one with nullable value

2 Answers2

Example for EF 6.0

Console Test