title: Put method for string instead of Id in generic repository
body: <p>I have a generic repository method for PUT which works fine and here it finds by the generic method of EF of primary key Id's.<br>
  What I am looking for is I want to update a record based on a specific column and its value is of type string. Is there a possibility to do this?</p>
  
  <pre><code>public virtual TEntity GetByID(object id)
  {
      return DbSet.Find(id);
  }
  </code></pre>