c# - 将两个具有不同对象的列表相交

Question

我有一个 ObjA 和 ObjB 列表，如下所示：

List<ObjA> List1;
List<ObjB> List2;

ObjA 和 ObjB 都有一个公共字段，即用户，我想根据 User.Id 将它们相交。

class ObjA
{ 
  User user;
  .... other properties
}

class ObjB
{ 
  User user;
  .... other properties
}

class User
{
    int Id;
     .... other props
}

如何将 User.Id 上的这两个列表与 linq 相交？

结果，我只想要用户列表。

Answer 1

总体思路是

var commonUsers = list1.Select(a => a.User).Intersect(list2.Select(b => b.User));

但是，这本身就假设Userimplements IEquatable<User>，这似乎不是这里的情况。因此，您要么需要添加此实现，要么使用Intersect接受自定义的重载IEqualityComparer<User>。

Answer 2

1.看这个简单的代码

  var result = (from objA in objAList
                join objB in objBList on objA.user.Id equals objB.user.Id
                select objA/*or objB*/).ToList();

2.完整的代码

 class QueryJoin
{
    static void Main(string[] args)
    {
        //create users
        User user1 = new User { Id = 1, Name = "anuo1" };
        User user2 = new User { Id = 2, Name = "anuo2" };
        User user3 = new User { Id = 3, Name = "anuo3" };
        User user4 = new User { Id = 4, Name = "anuo4" };
        User user5 = new User { Id = 5, Name = "anuo5" };
        //create objAList
        List<ObjA> objAList = new List<ObjA>();
        objAList.Add(new ObjA { user = user1 });
        objAList.Add(new ObjA { user = user2 });
        objAList.Add(new ObjA { user = user3 });
        //create objBList
        List<ObjB> objBList = new List<ObjB>();
        objBList.Add(new ObjB { user = user3 });
        objBList.Add(new ObjB { user = user4 });
        objBList.Add(new ObjB { user = user5 });

        //intersect
        var result = (from objA in objAList
                      join objB in objBList on objA.user.Id equals objB.user.Id
                      select objA/*or objB*/).ToList();

    }

}

class ObjA
{
    public User user { get; set; }
}

class ObjB
{
    public User user { get; set; }
}

class User
{
    public int Id { get; set; }
    public string Name { get; set; }
}

Answer 3

不需要 IEqualityComparer 或 IEquatable （反正会更好）

var commonUsers = list1
                  .Select(l1 => l1.User)
                  .Where(u => list1
                       .Select(l => l.User.Id)
                       .Intersect(list2
                          .Select(l2 => l2.Id))
                       .Contains(u.Id));

或者

var commonUsers = list1.Select(l1 => l1.User)
                      .Where(u=> list2.Select(l2 => l2.User.Id)
                                        .Contains(u.Id));

Answer 4

标准方法是利用IEqualityComparer对象。默认使用标准相等比较。创建一个实现IEqualityComparer接口并执行所需比较的类。然后你可以调用一个IEnumerable.Intersect接受自定义比较类实例的重载

Answer 5

您可以使用扩展方法 Linq

var result = List1.Join(List2, e1 => e1.ID, e2 => e2.ID, (e1, e2)=> e1);

欲了解更多信息，您可以访问https://www.tutorialsteacher.com/linq/linq-joining-operator-join