Storing database fields to a TComboBox

While there is a TDBLookupComboBox that allows the developer to attach the TDBLookupComboBox to a table directly, it does have some issues in its use. I prefer to use a normal TComboBox and feed it from a Query. It is then a standalone ComboBox that can be used for more than just updating a field in one table with a field in another.

But how do I fill the ComboBox? And once filled, how do I know which record the user has selected?

First the Query. I am assuming that, like me, you create a field in every table that is filled with a unique ID. I can use this ID in other tables to create a join. For example, I may have a Customer table ...

CustomerID: Integer
Name: String (e.g. VarChar)

Lets say I want a ComboBox of all my customers for the user to select. The query would look something like this ...

SELECT CustomerID, Name
FROM Customer
ORDER BY Name

I am always sure to ask for the ID first and then the text that the user will want to see. Now lets fill the ComboBox with that detail. Because I may wish to do this with many comboboxes in my application and with many different queries on other tables, I have built a procedure to fill the ComboBox using AddObject.

Procedure FillCombo(cb: TComboBox; Q: TQuery);
begin
   cb.items.clear;
  Q.First;
  while not Q.Eof do
   begin
       cb.Items.AddObject(Q.Fields[1].AsString, TObject(Q.Fields[0].AsInteger));
      Q.Next;
  end;
end;

Now I want to use that procedure to fill my ComboBox.

FillCombo(cbCustomer, MyQry);

So how then can we tell which record the user has selected? Simple, I have created a function that will return the ID of the selected record, in this case the selected Customer. If none has been selected, it will return -1.

function GetSelected(cb : TComboBox) : integer;
begin
   if cb.ItemIndex = -1 then
       result := -1
   else
       result := Integer(cb.Items.Objects[cb.ItemIndex]);
end;

So all we need to do is call it.

CustomerID := GetSelected(cbCustomer);
if CustomerID = -1 then
// none selected