title: instance of entity type cannot be tracked because another instance with same key value is tracked
body: <p>I'm using generic repository pattern in asp.net core 2.0 which can not dispose repository object, when I am going to update the entry its updated for one time successfully but when I am trying to update for more then once it throws the following exception:</p>
  
  <blockquote>
    <p>The instance of entity type 'Company' cannot be tracked because another instance with the same key value for {'ID'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the conflicting key values.</p>
  </blockquote>
  
  <pre><code>public ActionResult Edit(Int64 id, Company collection)
  {
      try
      {
          // TODO: Add update logic here
          interfaceobj.updateModel(collection);
          interfaceobj.Save();
          return RedirectToAction(nameof(Index));
      }
      catch(Exception ex)
      {
          throw ex;
      }
  }
  </code></pre>