C# linq 组到列表中的列表

Question

我有以下类(class)

public class UserManagementClass
    {
        public string userID;
        List<AgencyInfo> UserAgencyList;
    }

    public class AgencyInfo
    {
        public string userAgency;
        public string userAgencyName;
    }

现在这个列表可以有多个具有相同 userID 的实例，SQL 返回一个这样的列表:

 userID        userAgency      userAgencyName
    1           5    Milk Commission
    2           5    Milk Commission
    2           2    Department Of CSV

我翻译成这个:

[{
    "userID": "1",
    "AgencyInfo": [
        {
            "userAgency": "5",
            "userAgencyName": "Milk Commission"
        }
    ]
},
{
    "userID": "2",
    "AgencyInfo": [
        {
            "userAgency": "5",
            "userAgencyName": "Milk Commission"
        }
    ]
},
{
    "userID": "2",
    "AgencyInfo": [
        {
            "userAgency": "2",
            "userAgencyName": "Department Of CSV"
        }
    ]
}]

如何使用 Linq 将其分组为如下所示:

 [{
    "userID": "1",
    "AgencyInfo": [
        {
            "userAgency": "5",
            "userAgencyName": "Milk Commission"
        }
    ]
},
{
    "userID": "2",
    "AgencyInfo": [
        {
            "userAgency": "5",
            "userAgencyName": "Milk Commission"
        },
        {
            "userAgency": "2",
            "userAgencyName": "Department Of CSV"
        }
    ]
}]

我尝试使用多个非查询表达式但没有成功，有人可以指出正确的方向吗？

我的林克:

var UsersList = Users.GroupBy(u => u.userID).ToList();

Answer 1

使用 GroupBy 然后使用 Select 来定义您希望如何投影分组结果。

List<UserManagementClass> UsersList = Users
    .GroupBy(u => u.userID)
    .Select(_ => new UserManagementClass
    {
        userID = _.Key,
        UserAgencyList = _.SelectMany(u => u.UserAgencyList.Select(agency => agency)).ToList()
    }).ToList();