title: GroupBy with Linq to entities query
body: <p>I have following classes:</p>
  
  <pre><code>public class OrderItem
  {
       public int Id { get; set; }
       public ICollection&lt;NominalRouting&gt; NominalRoutings{ get; set; }
  }
  public class NominalRouting
  {
       public int Id { get; set; }
       public DateTime PlanedDate {get; set;} //yyyy/mm/dd
       public virtual Operation Operation{ get; set; }
  }
  public class Operation 
  {
       public int Id { get; set; }
       public string Code { get; set; }
       public virtual AreaSpecification AreaSpecification{ get; set; }
  }
  public class AreaSpecification 
  {
       public int Id { get; set; }
       public string Title { get; set; }
  }
  </code></pre>
  
  <p>I have following data:</p>
  
  <pre><code>-----------------------------------------------------------
  | OrderItemId |  AreaTitle | Operation Code | PlannedDate |
  -----------------------------------------------------------
  |      1      |    Area1   |       OP1       | 2016/01/01 |
  |      1      |    Area1   |       OP2       | 2016/01/02 |
  |      1      |    Area1   |       OP3       | 2016/01/03 |
  |      1      |    Area2   |       OP4       | 2016/02/01 |
  |      1      |    Area2   |       OP5       | 2016/02/02 |
  |      1      |    Area3   |       OP6       | 2016/03/01 |
  |      1      |    Area3   |       OP7       | 2016/03/04 |
  |      1      |    Area3   |       OP7       | 2016/03/08 |
  -----------------------------------------------------------
  </code></pre>
  
  <p>How can I write a linq to entities(method syntax) query using EF code first, to <code>GroupBy</code> above data by <code>AreaTitle</code> and get following result(earlear <code>PlannedDate</code> in each <code>AreaTitle</code>)?:</p>
  
  <pre><code>-----------------------------------------------------------
  | OrderItemId |  AreaTitle | Operation Code | PlannedDate |
  -----------------------------------------------------------
  |      1      |    Area1   |       OP1       | 2016/01/01 |
  |      1      |    Area2   |       OP4       | 2016/02/01 |
  |      1      |    Area3   |       OP6       | 2016/03/01 |
  -----------------------------------------------------------
  </code></pre>