title: Why we need to attach a selftracking entity to context before deleting?
body: <p>I have a service which will add , update and delete a patient entity . 
  I made the patient entity is selftracking entity .</p>
  
  <p>But only for delete i need to call 'Attach'  the entity before deleting , why not attach required for add and update .</p>
  
  <p>What is the logic behind attaching only for delete ( I have cascading property = true) </p>
  
  <pre><code> public List&lt;Patient&gt; AddPatient(Patient pat)
      {
  
  
          DataBaseContext.Patients.AddObject(pat);           
          DataBaseContext.SaveChanges();
          return DataBaseContext.Patients.Include("PatientContacts").ToList();
  
      }
  
      public List&lt;Patient&gt; DeletePatient(Patient pat)
      {
  
         //Why only for delete we need to attach ??????????
  
          DataBaseContext.Patients.Attach(pat);
          DataBaseContext.Patients.DeleteObject(pat);
          DataBaseContext.SaveChanges();
          return DataBaseContext.Patients.Include("PatientContacts").ToList();
      }
  
      public List&lt;Patient&gt; UpdatePatient(Patient pat)
      {
  
           DataBaseContext.Patients.ApplyChanges(pat);
           DataBaseContext.SaveChanges();
           return DataBaseContext.Patients.Include("PatientContacts").ToList();
      }
  </code></pre>