[英]Filter a list of objects using a property that is another list. Using linq
I've a nice situation, I think at beginning this a usual query but I'm having some problem trying to solve this, the situation is: 我有一个很好的情况,我认为在开始这是一个常见的查询,但我有一些问题试图解决这个问题,情况是:
I've a list of "Houses", and each house have a list of "Windows". 我有一个“房子”列表,每个房子都有一个“Windows”列表。 And I want to filter for a catalog only the Houses witch have a Blue windows, so my extension method of House is something like:
而且我想过滤一个目录,只有那个女巫有一个蓝色的窗户,所以我的扩展方法是这样的:
public static List<House> FilterByWindow (this IEnumerable<House> houses, Window blueOne){
var list = houses.Select(p=>p.Windows.Where(q=>q.Color == blueOne.Color));
return list.ToList();
}
Is this correct or I'm losing something? 这是正确的还是我失去了什么? Some better suggestion?
一些更好的建议?
If you want to search for House
instances containing blue Windows
, then use the existing Any
extension: 如果要搜索包含蓝色
Windows
House
实例,请使用现有的Any
扩展:
var blueWindowHouses =
from h in houses
where h.Windows.Any(w => w.Color == blueOne.Color)
select h;
What you have right now is not correct. 你现在拥有的是不正确的。 The
Select
extension does not filter - it is a projection, and you aren't assigning the result to anything, so that line you have is effectively a no-op. Select
扩展名不会过滤 - 它是一个投影,并且您没有将结果分配给任何内容,因此您拥有的行实际上是一个无操作。
Also, by wrapping this logic in a method, you can prevent the expression compiler from being able to translate it into a SQL statement. 此外,通过将此逻辑包装在方法中,可以防止表达式编译器将其转换为SQL语句。 Instead, write it all in one shot, as I have above, or accept and return an
IQueryable<House>
instead of accepting an IEnumerable<House>
and returning a List<House>
. 相反,如上所述,一次性写入,或接受并返回
IQueryable<House>
而不是接受IEnumerable<House>
并返回List<House>
。
return houses.Where(house => house.Windows.Any(window => window.Color == blue))
.ToList();
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