以应用多张标准中lambda表达式在c＃(To apply mulitple criteria in

I have two main tables Listings and Place . In listing table there is a field PlaceId which referes to a Place entity/row/object . I want to query on both tables so that i get both of them like this .

 var query = context.Listings
       .Include("Place")
       .Where(l => l.Place.TypeId == Type.Ro)
       .OrderBy(l => l.Id).ToList();

after this now i want to put some filter on this query , here is the condition .

i got only a string like this var filter = "1,2,4"; . Now i want to filter on listing to gett all these listing where bedroom is equal to 1 OR 2 OR 4 .

What i have done

 string minBeds = "1,2,4";

 foreach (var item in minBeds.Split(','))
 {
      int minBed = int.Parse(item);
      query = query.Where(l=>l.Place.Bedroom == minBed).ToList();
 }

But doing this is giving me Zero result.

Answer 1:

与你过滤的方式的问题。 第一遍后，你过滤掉，除非一切Bedroom == 1 ，在第二次你过滤掉，除非一切Bedroom == 2 ，但因为在列表中唯一的项目有Bedroom == 1 ，你不会有结果集东西。

解决的办法是使用传统的C＃ || 运营商：

query = query.Where(l => l.Place.Bedroom == "1" || 
                         l.Place.Bedroom == "2" || 
                         l.Place.Bedroom == "4");

或者，如果你想成为更灵活，可以使用Contains方法：

string[] minBeds = "1,2,4".Split(',');
query = query.Where(l => minBeds.Contains(l.Place.Bedroom));

注意：如果Bedroom是一个整数，你需要输入转换成合适的类型第一：

var minBeds = "1,2,4".Split(',').Select(int.Parse);
query = query.Where(l => minBeds.Contains(l.Place.Bedroom));

另外请注意，我已经消除了ToList这里。 除非你需要通过指数从结果集合访问项目，并添加/删除项目，这是最有可能只是浪费资源。 通常你可以依靠的LINQ的原生懒惰延迟处理查询，直到你真正需要的结果。

文章来源: To apply mulitple criteria in lambda expression in c#