Check if item exists
You make this harder then it needs to be.

Since IDbSet implements the IEnumerable&lt;TEntity&gt; interface


 public interface IDbSet&lt;TEntity&gt; 
 : IQueryable&lt;TEntity&gt;, IEnumerable&lt;TEntity&gt;, IQueryable, IEnumerable



you can simply use the Contains extension optionally with your own comparer that can implement such things as Trim etc.