Question

在LINQ中有没有办法做一个OrderBy，然后用ThenBy做一个ThenBy，使用父对象的子进行二次排序？

_repository.GetActiveDepartmentGroupsWithDepartments().OrderBy(c => c.DepartmentGroupName).ThenBy(c => c.Departments.OrderBy(d => d.DepartmentName))

在上面的例子中，c.Departments是一个EntityCollection。

顺便说一句：当我尝试上面的内容然后对其执行ToList（）时，我收到此错误：

DbSortClause expressions must have a type that is order comparable.
Parameter name: key

提前感谢您的任何帮助或指导。

Answer 1

您似乎正在尝试获取按组和部门名称排序的所有部门的列表。如果是这样，那么你可能想做这样的事情：

var res = from c in _repository.GetActiveDepartmentGroupsWithDepartments()
          from d in c.Departments
          orderby c.DepartmentGroupName, d.DepartmentName
          select d;

或者在方法语法中：

var res = _repository.GetActiveDepartmentGroupsWithDepartments()
                     .SelectMany(c => c.Departments, (c,d) => new { c, d })
                     .OrderBy(x => x.c.DepartmentGroupName)
                     .ThenBy(x => x.d.DepartmentName)
                     .Select(x => x.d);

Answer 2

由于Deparment是一个集合，你必须将它转换为标量才能用于排序。

一种选择是在集合中选择单个实体，例如第一部门的名称：

_repository.GetActiveDepartmentGroupsWithDepartments()
   .OrderBy(c => c.DepartmentGroupName)
   .ThenBy(c => c.Departments
       .OrderBy(d => d.DepartmentName)
       .FirstOrDefault()
       .DepartmentName
    )

另一种选择是通过集合本身的属性来订购，例如部门数量：

_repository.GetActiveDepartmentGroupsWithDepartments()
   .OrderBy(c => c.DepartmentGroupName)
   .ThenBy(c => c.Departments.Count())

LINQ OrderBy Name ThenBy ChildrenCollection.Name

2 个答案: