1 public static IQueryable<TSource> WhereIn<TSource, TKey>(this IQueryable<TSource> source1, Expression<Func<TSource, TKey>> keySelector, IEnumerable<TKey> source2)
 2         {
 3             if (null == source1)
 4                 throw new ArgumentNullException("source1"); 
 5             if (null == keySelector)
 6                 throw new ArgumentNullException("keySelector"); 
 7             if (null == source2)
 8                 throw new ArgumentNullException("source2"); Expression where = null;
 9             foreach (TKey value in source2)
10             {
11                 Expression equal = Expression.Equal(keySelector.Body, Expression.Constant(value, typeof(TKey)));
12                 if (null == where)
13                     where = equal;
14                 else
15                     where = Expression.OrElse(where, equal);
16             }
17             return source1.Where<TSource>(Expression.Lambda<Func<TSource, bool>>(where, keySelector.Parameters));
18         }