LINQ OrderBy名稱ThenBy ChildrenCollection.Name

Question

有沒有什麼辦法在LINQ做OrderBy，然後用ThenBy做一個ThenBy使用父對象的子對象進行二級排序？

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

在上面的例子中，c.Departments是一個EntityCollection。

BTW：當我嘗試了上面，然後做一個ToList（）就可以了，我得到這個錯誤：

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

預先感謝任何幫助或指導。

Answer 1

看起來好像你正試圖獲得所有按部門命名的部門名單，然後是部門名稱。如果是這樣，那麼你可能想要做這樣的事情：

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

還是在方法的語法：

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

由於百貨商店是一個集合，你必須把它轉化爲一個標量使用它排序。

一種選擇是選擇集合中的單個實體，例如，第一部門的名稱：

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

另一種選擇是通過集合本身的屬性（例如，部門數：

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