LINQ OrderBy Name ThenBy ChildrenCollection.Name
Is there any way in LINQ to do an OrderBy and then do a ThenBy with the ThenBy using the children of the parent object to do the secondary ordering?
_repository.GetActiveDepartmentGroupsWithDepartments().OrderBy(c => c.DepartmentGroupName).ThenBy(c => c.Departments.OrderBy(d => d.DepartmentName))
In the above case, c.Departments is an EntityCollection.
BTW: When I try the above and then do a ToList() on it, I get this error:
DbSortClause expressions must have a type that is order comparable.
Parameter name: key
Thanks in advance for any help or guidance.
It seems like you're trying to get a list of all departments ordered by group then department name. If so, then you probably want to do something like this:
var res = from c in _repository.GetActiveDepartmentGroupsWithDepartments()
from d in c.Departments
orderby c.DepartmentGroupName, d.DepartmentName
select d;
Or in method syntax:
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);
Since Deparment is a collection, you have to transform it to a scalar to use it for sorting.
One option is to select a single entity to in the collection, eg the name of the first department:
_repository.GetActiveDepartmentGroupsWithDepartments()
.OrderBy(c => c.DepartmentGroupName)
.ThenBy(c => c.Departments
.OrderBy(d => d.DepartmentName)
.FirstOrDefault()
.DepartmentName
)
Another option is to order by a property of the collection itself, eg the number of departments:
_repository.GetActiveDepartmentGroupsWithDepartments()
.OrderBy(c => c.DepartmentGroupName)
.ThenBy(c => c.Departments.Count())