title: What is HashSet in MVC
body: <p>I am new in MVC, so I have problem to understand what is purpose of HashSet in model.
  I am using ADO.net Entity Data model, system auto generate model like ..</p>
  
  <pre><code>public partial class Country
  {
      public Country()
      {
          this.States = new HashSet&lt;State&gt;();
      }
  
      public int ID { get; set; }
      public string Name { get; set; }
  
      public virtual ICollection&lt;State&gt; States { get; set; }
  }
  </code></pre>
  
  <p>any one can explain in simple language why I should use a HashSet here?</p>