title: SaveChanges in Entity Framework causes error Validation failed for one or more entities. See 'EntityValidationErrors'
body: <p>I have added the patient and visit tables in <code>reg_visit</code> table in Entity Framework 6.1 code-first
  but when run the below code, I get this error:</p>
  
  <blockquote>
    <p>Validation failed for one or more entities. See 'EntityValidationErrors' property for more details.</p>
  </blockquote>
  
  <p>Code:   </p>
  
  <pre><code>Models.VisitDoctotDb oVisitdb = new Models.VisitDoctotDb();
  Models.RegVisit oReg_visit = new Models.RegVisit();
  
  oReg_visit.Patient = oPatient;
  oReg_visit.Visit = oVisit;
  
  oVisitdb.Reg_visit.Add(Reg_visit); ===&gt; error
  oVisitdb.SaveChanges();
  </code></pre>