title: What kind of property is this? is it necessary?
body: <p>When creating a mapping, I am reading that your collection property should look like:</p>
  
  <pre><code>  public virtual ReadOnlyCollection&lt;Product&gt; Products
    {
             get { return new ReadOnlyCollection&lt;Product&gt;(new List&lt;Product&gt;(_products).AsReadOnly()); }
    }
  </code></pre>
  
  <p>Why does it have to be like this? it seems to be returning a new collection everytime it is referenced?</p>