Master-detail with two DBLookupComboBoxes
lazarus / 16-Databases

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percentage · 2013-12-21 15:27

Lazarus 1.0.14, Zeos 7.1.2, VirtualDBGrid, Firebird.

I have three tables. Two list tables, Car and Model, each have FKs in
a Garage table. Between the Car and Model tables there is a M-D
relationship (TZQueries). On a form I have two DBLookupComboBoxes with
ListSources connected each to Car and Model, and both DataSources to
Garage, to update the FKs.

What I want: when I select a Car in the first DBLookupComboBox, the
second one should display only the Models of the selected car. I tried
among other things to set the ScrollListDataset of the master
DBLookupComboBox to True, but it doesn't work. The dbl-combo that
should display the model only shows the models for the first primary
key from the Car table.

If I connect two grids to Car and Model, I see the M-D working like it
should. How do you do it with DBLookupComboBoxes?

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CaptBill · 2013-12-21 16:33

You should simply need to catch the onchange event of the master table
"cars" then query or filter the detail table "models".

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percentage · 2013-12-22 13:30

Thanks, I tried your suggestion and it worked. I removed the M-D
relationship between the queries and I put this in the OnChange event
of the DBLookupComboCar:

with QueryModel do
begin
  Filter:='IDCAR = ' + QuotedStr(DBLookupComboCar.KeyValue);
  Close;
  Open; // Refresh doesn't work.
end

In my opinion, it should have worked out of the box after setting the
M-D relationship, no filtering required, like grids. But now there is
the question of efficiency. Which one is better? M-D between queries,
or setting up a filter?