title: How to create One to One Relationship using EDMX and POCO entities (database first)
body: <p>I have 2 entities:</p>
  
  <pre><code>public class User
  {
       public int UserId{ get; set; } //Primary Key
       public string UserName{ get; set; }
  
       public virtual Protocol MyProtocol{ get; set; } //Navigation
  }
  
  public class Protocol
  {
       public int ProtocolId{ get; set; } //Primary Key
       public string ProtocolNumber{ get; set; }
       public int UserId{ get; set; } //Unique Key
  
       public virtual User Owner{ get; set; } //Navigation
  }
  </code></pre>
  
  <p>In EDMX relationship map, I setted:</p>
  
  <blockquote>
    <p>End1 Multiplicity 1(User). 
    End2 Multiplicity 0..1(Protocol).</p>
  </blockquote>
  
  <p>I can't even build project, build throws:</p>
  
  <p>Error 113: Multiplicity is not valid in Role 'Protocol' in relationship 'FK_Protocol_User'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be *.  </p>
  
  <p>Is there a way to do this, or User must have a Collection of Protocol even when he'll never have more than one protocol?</p>