/// <summary>
 /// Creates sources for consequitive expressions .Where, .OrderBy, etc.
 /// </summary>
 /// <param name="provider"></param>
 /// <param name="expression"></param>
 internal QueryableWorkItemStore(WorkItemQueryProvider provider, Expression expression)
 {
     this.provider = provider;
     this.expression = expression;
 }
 /// <summary>
 /// Creates source for initial expression, i.e. From
 /// </summary>
 /// <param name="provider"></param>
 internal QueryableWorkItemStore(WorkItemQueryProvider provider)
 {
     this.provider = provider;
     this.expression = Expression.Constant(this);
 }