title: IEnumerable<> instead of List<> goes well when reading objects
body: <p>Consider my following class Album:</p>
  
  <pre><code>public class Album
  {
      public int? Id { get; set; }
      public string Name { get; set; }
      public IEnumerable&lt;Photo&gt; Photos { get; set; }
      public DateTime Registered { get; set; }
  }
  </code></pre>
  
  <p>I have no troubles retrieving data out and populating my album and my photo collection. </p>
  
  <p>However now I also want to 'Add' a Photo item into my Photos collection, 'Add' is not recognized as a valid method on Photos.</p>
  
  <blockquote>
    <p>'System.Collections.Generic.IEnumerable'does not contain a
    definition for 'Add' and no extension method 'Add' accepting a first
    argument of type....</p>
  </blockquote>
  
  <p>What should I do as a simple thing to get it to work with IEnumerable? I don't want to change my property to </p>
  
  <pre><code>public List&lt;Photo&gt; Photos { get; set;}
  </code></pre>
  
  <p>Do I really need to implement ICollection on my Album class?</p>
  
  <pre><code> public class Album : ICollection&lt;Photo&gt; { ... }
  </code></pre>