Complex linq query to validate sum of child units using the same datatable

I have the following datatable, which has Units information. The Units have a surface in 开发者_运维技巧square meters. However the units can be split into subunits, in the datatable there is a ParentUnitID to know if that unit is splitted or not.

I need to validate that the sum of the surface of the child units, is equal to the surface of the parent unit.

The current code is something like:

private void ValidateUnitsStep(WorkspaceCancelEventArgs e)
{
    //Get data from step
    GetUnitsData();
    UserControlUnits Units = GetSmartPartByType<UserControlUnits>();

    if (_unitDataSet.Unit.HasErrors)
    {
        e.Cancel = true;
    }

    DataRow[] rows = _unitDataSet.Unit.Select("ParentUnitId !=" + string.Empty);
            foreach(DataRow dr in rows)
    {

    }
}

I would like to do this with LINQ.

Edit: Yes, thats also possible, up to 2 levels of childs only

Unit A (100 sqm)

-UnitA1 (70)

  -UnitA11 (20)

  -UnitA12 (20)

  -UnitA12 (30)

-UnitA2 (30)

  -UnitA21 (20)

  -UnitA22 (10)

---

A possible implementation using linq to DataSet

(1 level of children, but I'm sure you can work out for 2 levels)

// Group the records by parent ID (potentially null)
var childrenByParentID = _unitDataSet.Unit.AsEnumerable().
                         ToLookup(child => child.Field<int?>("ParentUnitId"));

// Parents = children with no parent
var parentsByID = childrenByParentID[null].ToLookup(parent => parent.Field<int>("UnitID"));

// Look for the first group which sum of surfaces is not the same as the parent's surface
var invalidGroup = childrenByParentID.FirstOrDefault(group => 
{
  bool invalid = false;  

  if (group.Key != null)
  {
    // Not the parents group
    var currentParent = parentsByID[group.Key]);

    var totalSurface = group.Sum(row => row.Field<int>("Surface"));
    invalid = (totalSurface != currentParent.Field<int>("Surface"));
  }

  return invalid;
});

if (invalidGroup != null)
{
  // .. do something special
}