Linq 查询包含

Question

我对此查询有疑问

  var myList = (from p in db.Full
                      where (p.date_reception > begin & p.date_reception < end
                            & !p.mc_owner.Contains("NULL") & !p.mc_owner.Contains(""))

                      group p by p.mc_owner into g
                      orderby g.Count() descending
                      select new
                      {
                          Ownerx = g.Key,
                          countx = g.Count()
                      }).ToList();

没有添加 !p.mc_owner.Contains("") 一切正常，但是一旦我添加它就没有显示任何结果

Answer 1

任何有值的字符串都将包含空字符串。例如下一个测试代码将打印 true.

    string a = "abc";
    Console.WriteLine(a.Contains(""));
    Console.ReadLine();

您可能打算写：

p.mc_owner != ""

还是写

比较好

!string.IsNullOrEmpty(p.mc_owner)

我猜想在 .contains("NULL") 中你想省略 NULL 值而不是字符串 "NULL"。我也会用 && 而不是 &。我建议重写为：

(p.date_reception > begin && p.date_reception < end
                        && !string.IsNullOrEmpty(p.mc_owner))

Answer 2

我的做法是：

   var myList = (from p in db.Full
                      where (p.date_reception > begin & p.date_reception < end
                            & !p.mc_owner.Contains("NULL") & !string.IsNullOrWhiteSpace(p.mc_owner))

                      group p by p.mc_owner into g
                      orderby g.Count() descending
                      select new
                      {
                          Ownerx = g.Key,
                          countx = g.Count()
                      }).ToList();

Linq 查询包含

Linq query Contains

c#

linq

entity-framework

contains

asp-classic