title: Using Join, Group By, and Sum in Entity Framework
body: <p>My models look like:</p>
  
  <pre><code>public class ReturnItem
  {
      public int returnItemId { get ; set; }
      public int returnRequestId { get; set; }
      public int quantity { get; set; }
      public string item { get; set; }
  }
  
  public class ReturnRequest
  {
      public int returnRequestId { get; set; }
      public string orderNumber  { get; set; }
      public IEnumerable&lt;ReturnItem&gt; returnItems { get; set; }
  }
  </code></pre>
  
  <p>And I have the following query:</p>
  
  <pre><code>SELECT item, sum(quantity)
  FROM ReturnItem
  JOIN ReturnRequest
  ON ReturnRequest.returnRequestId = ReturnItem.returnRequestId
  WHERE ReturnRequest.orderNumber = '1XX'
  GROUP BY item
  </code></pre>
  
  <p>How do I convert the query to Entity Framework and return a <code>List&lt;ReturnItem&gt;</code>? Can I use <code>.Include</code> instead of <code>.Join</code>?</p>