[英]LINQ: Filter by value in sub list
我已经获得了这样的列表:
int[] listOfUserIds = new int[]{1,2,5};
var groups = db.some_table.Where(x => x.isOpen == true)
.Select(t => new Models.XModel() {
Id = t.Id,
Name = t.name,
Users = t.Users.Where(x => x.Age > 25).Select(user => new Models.UsersModel()
{
Name = user.Name,
UserId = user.UserId
})
});
现在,从这个groups
列表中,我想获取至少有一个UserId
在listOfUserIds
内的user
的listOfUserIds
。
如何在没有 for 循环的情况下轻松实现这一目标?
在您的Where
子句中再添加 1 个条件:
x.Users.Any(user => listOfUserIds.Contains(user.UserId))
您的代码:
var groups = db.some_table.Where(x => x.isOpen == true && x.Users.Any(user => listOfUserIds.Contains(user.UserId)))
.Select(t => new Models.SomeModel() {
Id = t.Id,
Name = t.name,
Users = t.Users.Where(x => x.Age > 25).Select(user => new Models.UsersModel()
{
Name = user.Name,
UserId = user.UserId
})
});
为了提高性能,您可以构建一个HashSet<int>
:
int[] listOfUserIds = new int[]{1,2,5};
HashSet<int> hash = new HashSet<int>(listOfUserIds);
var groups = db.some_table.Where(x => x.isOpen == true && x.Users.Any(user => hash.Contains(user.UserId)))
.Select(t => new Models.SomeModel() {
Id = t.Id,
Name = t.name,
Users = t.Users.Where(x => x.Age > 25).Select(user => new Models.UsersModel()
{
Name = user.Name,
UserId = user.UserId
})
});
使用HashSet<int>
,这个操作hash.Contains(x.Id)
是O(1)而不是O(n)
和listOfUserIds
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