//构造Lambda语句

        private static Expression<Func<TElement, bool>> BuildWhereInExpression<TElement, TValue>(Expression<Func<TElement, TValue>> propertySelector, IEnumerable<TValue> values)

         {

             ParameterExpression p = propertySelector.Parameters.Single();

             if (!values.Any())

                 return e => false;

            var equals = values.Select(value => (Expression)Expression.Equal(propertySelector.Body, Expression.Constant(value, typeof(TValue))));

             var body = equals.Aggregate<Expression>((accumulate, equal) => Expression.Or(accumulate, equal));

            return Expression.Lambda<Func<TElement, bool>>(body, p);

         }

//调用

       string[] ids = new string[]{"id1","id2","id3"}；

       db.ProjectFiles.Where(BuildWhereInExpression<Profile,int>(v=>v.Id,ids);

//封装方法

        public static IQueryable<TElement> WhereIn<TElement, TValue>(this IQueryable<TElement> source, Expression<Func<TElement, TValue>> propertySelector, params TValue[] values)

         {

             return source.Where(BuildWhereInExpression(propertySelector, values));

         }

 //直接使用下列方法调用

      string[] ids = new string[]{"id1","id2","id3"}；

       db.ProjectFiles.WhereIn(c => c.Id,ids);

 //字符串构造

 //这个方法比较简单

      string[] ids = new string[]{"id1","id2","id3"}；

       cstIds=cstIds.Replace(",","','");

       var query = db.ProjectFiles.Where("it.Id in {'" + cstIds + "'}");