Question

我有以下Linq声明：

var permissions = (from ru in RoleUserStore
                  join role in RoleStore on ru.RoleId equals role.Id
                  where ru.UserId == user.Id
                  select role.Permissions).ToList();

我的结果是List<ICollection<Permission>>。如何正确执行此操作以在所有角色中拥有一个平面列表？我无法弄清楚如何做到这一点。

Answer 1

将ToList()替换为SelectMany(x => x).ToList()。

Answer 2

使用查询语法中的SelectMany：

var permissions = from ru in RoleUserStore
                  join role in RoleStore on ru.RoleId equals role.Id
                  where ru.UserId == user.Id
                  from permission in role.Permissions
                  select permission;

 // if you don't want repeating permissions use Distinct:
List<Permission> permissionList = permissions.Distinct().ToList();

请注意，您需要在Equals中实施GetHashCode和Permission才能有意义地使用Distinct。

Answer 3

您可以使用SelectMany

var result = (from ru in RoleUserStore
              join role in RoleStore on ru.RoleId equals role.Id
              where ru.UserId == user.Id
              select role.Permissions)
              .SelectMany(user => user).ToList();

这就是SelectMany所做的，我引用了MSDN。

Projects each element of a sequence to an IEnumerable(Of T) and flattens the resulting sequences into one sequence.

Linq Join选择返回展平列表

3 个答案: