Field values when using projections

BIZ TMS Aurelius
1
I am trying to populate a DBGrid with a result set from an Aurelius ORM query.

This is the SQL that works:
  select max(c_date), st.last, st.first, st.id_student from tblContact c
  inner join tblstudent st on st.id_student = c.id_student
  group by st.id_student
  order by c_date

To start, I created a simple query with no projections:
  AureliusDataset2.SetSourceCriteria(AMgr.Find<TtblContact>().OrderBy('c_date'));
This populates the grid with values.

But when I tried to add my "group by" and "max" projections, nothing displays in my DBGrid: 
  AureliusDataset2.SetSourceCriteria(AMgr.Find<TtblContact>()
    .SetProjections(TProjections.ProjectionList
    .Add(TProjections.Group('id_student'))
    .Add(TProjections.Max('c_date')))
    .OrderBy('c_date')
    );

I also tried it with DBAdvGrid, with same results.

What is missing from my ORM query that I get a list of records but no fields in my grid?

Thanks in advance to everyone for your help.  I learn a lot from following your posts.
2

Hello Jon,

When using projections (TCriteriaResult objects) you have to create the the dataset fields yourself in advance. Just use aliases and create fields with names, i.e.:



 AureliusDataset2.SetSourceCriteria(AMgr.Find<TtblContact>()
    .SetProjections(TProjections.ProjectionList
    .Add(TProjections.Group('id_student').As_('student'))
    .Add(TProjections.Max('c_date').As_('maxdate')))
    .OrderBy('c_date')
    );

For example, create two fields, student and maxdate in your dataset.
3

For the benefit of future souls... So if a given query has projections then Arelius doesn't return entities. But we can still output data to the dataset for DB aware components by creating aliases for the fields we want?

4

Yes, correct.