How do you correctly return an aggregate data field using AX 2012 Query Service

I have been working on the AX Query Service as of late. I have a pretty good understanding of everything but it seems that the QueryDataFieldMetadata object does not like aggregates. When I build a QueryDataFieldMetadata object:

QueryDataFieldMetadata field = new QueryDataFieldMetadata();
field.TableName = "InventSum";
field.FieldName = "AvailPhysical";
field.SelectionField = SelectionField.Database;

And add it to the data source everything is fine. But when I do this:

QueryDataFieldMetadata field = new QueryDataFieldMetadata();
field.TableName = "InventSum";
field.FieldName = "AvailPhysical";
field.SelectionField = SelectionField.Sum;

And add it to the data source the field is not returned at all in the results set. I have checked the datasource itself before executing the query and it is in the fields list but nothing is returned. Does anyone know why this might be happening? Any help would be appreciated.

I just figured this one out. The problem was due to me selecting another field from the table but forgetting to put it in the "Group by" fields. It is strange to me that the query service was returning THAT field with an empty but not returning the aggregate fields at all. Basically I had made a query service query that would be equal to this:

Select wMSLocationId, SUM(AvailPhysical), RecId from InventSum group by ItemId, InventLocationId, wMSlocationId where ItemId == 'some value';

The query was returning:

InventSum.wMSLocationId = 001

InventSum.RecId = 0

The inclusion of the RecId was a mistake, I had forgotten to remove it, but didn't think it would matter as it wasn't in the group by fields and would therefore return null. Removing this selection field did result in the aggregate field returning in the query.

Anyway I hope this helps someone out there as it took me some time to figure out.