Question

courses = courses.Where(
                c => queryParameters.ShowInActive || c.Flags.Contains((ulong)CourseFlags.Active) 
                     &&
                     (queryParameters.AuthorId <= 0 ||
                      (c.Authors != null && c.Authors.Exists(a => a.ID == queryParameters.AuthorId)))
                     &&
                     (queryParameters.CategoryIDs == null || queryParameters.CategoryIDs.Count == 0 ||
                      (c.Tags != null && c.Tags.Any(t => queryParameters.CategoryIDs.Contains(t.ID)))
                      &&
                      queryParameters.CourseIDs == null || queryParameters.CourseIDs.Count == 0 ||
                      queryParameters.CourseIDs.Contains(c.ID))
                ).ToList();

问题是queryParameters.CourseIDS.Count()返回157，但上面的lambda表达式返回2500条记录。我究竟做错了什么？

我还确保ShowInactive设置为true，CategoryIDs为空，AuthorId为0

Answer 1

tl;博士：你忘记了一些括号。

如上所述，当queryParamters.ShowInActive设置为true时，谓词将返回true并返回所有记录。因此，返回所有记录。您似乎想要使用所有查询参数。为清晰起见，请尝试在此复杂查询中添加一些空格。或者考虑将其拆分为多个Where()来电。

courses = courses.Where(
              c => (
                    queryParameters.ShowInActive
                    ||
                    c.Flags.Contains((ulong)CourseFlags.Active)
              ) && (
                    queryParameters.AuthorId <= 0
                    || (
                        c.Authors != null
                        &&
                        c.Authors.Exists(a => a.ID == queryParameters.AuthorId)
                       )
              ) && (
                    queryParameters.CategoryIDs == null
                    ||
                    queryParameters.CategoryIDs.Count == 0
                    || (
                        c.Tags != null
                        &&
                        c.Tags.Any(t => queryParameters.CategoryIDs.Contains(t.ID))
                       )
              ) && (
                    queryParameters.CourseIDs == null
                    ||
                    queryParameters.CourseIDs.Count == 0
                    ||
                    queryParameters.CourseIDs.Contains(c.ID)
                   )
              )
            ).ToList();

Answer 2

问题在于运营商的优先级，特别是＆amp;＆amp;优先级高于||。因此，如果不花太多钱，请尝试以下方法：

courses = courses.Where(
            c => (queryParameters.ShowInActive || c.Flags.Contains((ulong)CourseFlags.Active))
                 &&
                 (queryParameters.AuthorId <= 0 ||
                  (c.Authors != null && c.Authors.Exists(a => a.ID == queryParameters.AuthorId)))
                 &&
                 ((queryParameters.CategoryIDs == null || queryParameters.CategoryIDs.Count == 0 ||
                  (c.Tags != null && c.Tags.Any(t => queryParameters.CategoryIDs.Contains(t.ID))))
                  &&
                  (queryParameters.CourseIDs == null || queryParameters.CourseIDs.Count == 0 ||
                  queryParameters.CourseIDs.Contains(c.ID)))
            ).ToList();

我的lambda表达式没有产生我预期的结果

2 个答案: