title: EF 6 Database First Code generation item
body: <p>I use Entity Framework 6 Database First with Visual Studio 2015.
  Sometimes when I modify .edmx diagram and save changes, all .cs class(for tables) are deleting from code generation model.tt file and I could not make these return.
  Just for create Entity Data Model from zero, too.</p>
  
  <p>Anybody know what is the reason of this problem, end how should I solve this?</p>
  
  <p>Thanks any helps.</p>
  
  <p><strong>I have modified my entity data model with this:</strong>(Not know it can be the reason or other)</p>
  
  <p>*<a href="https://stackoverflow.com/questions/13181739/ef5-grdiview-only-count-readonly">EF5 Grdiview only Count &amp; ReadOnly</a>
  /<em>After that open yourModel.tt file
  Find and replace the two occurrences of “ICollection” with “ObservableListSource” (lines 296 and 484).
  Find and replace the first occurrence of “HashSet” with “ObservableListSource” ( Line 50).
  Do not replace the second occurrence of HashSet found later in the code.</em>/*</p>