ADO Updateable Queries - error when a one of the joined tables has no record - sql

Question

I use the 'updateable query' feature of ADO, being able to select a dataset from several tables and criteria and display it in a grid or some other UI for the user to browse and edit.
However, and I'm surprised I've not hit this problem before now, when one of the joined tables doesn't have a record for the (master) key, and the user tries to edit a field in that table, ADO gives the famous "Row cannot be located.." error on post.
As far as I understand this error, the ADO driver is trying to locate the record in order to update its fields - and, of course, in this instance, there is no record to find. What I was expecting in these circumstances would be that the ADO driver would issue the equivalent of an UPDATE query for the main table, but an INSERT query for the subsidiary table.
Has anyone else come across this problem and found a workround?
The ADO driver used is the Jet 4.0 OLE DB Provider connecting to an Access (mdb) database.
I have ensured that the primary keys fields for both tables are available in the query dataset for the driver to utilise.
Here is a basic version of the SQL I have using:
SELECT
Table1.CustomerNo, Table1.Field1, Table1.Fieldn,
Table2.CustomerNo, Table2.Field1, Table2.Fieldn
FROM
Table1
LEFT JOIN Table2
ON Table1.CustomerNo = Table2.CustomerNo
WHERE
Table1.CustomerNo = Newcode;
As an experiment, I tried the same thing in MS Access 2007, and that worked, so there maybe a solution within ADO (but then Access is probably using a different driver).

Answer 1

In the end, I went for the 'hack' solution. The updateable ADO query over 2 tables would only work if
the customer's reocrds existed in both tables. So, I had to check that, and if the relevant record was missing from table2, had to insert it first, before calling the main query. Here is the code:
//Query customer account - open query from Table1 and Table2 tables
TwoTableQuery.Close;
//
//SELECT Table2.CustomerNo
// FROM Table2
//WHERE (Table2.CustomerNo = CustomerCode);
Table2Query.Close;
Table2Query.Parameters[0].Value := CustomerCode;
Table2Query.Open; /
//does the Table2 record exist for this customer?
if Table2Query.RecordCount = 0 then
begin //no, so create a new record
Table2Query.Insert;
Table2Query.FieldByName('CustomerNo').AsString := CustomerCode;
Table2Query.Post;
Table2Query.Close;
end;
//okay, now okay to open main query
TwoTableQuery.Parameters[0].Value := CustomerCode;
TwoTableQuery.Open;
It's not efficient, and also creates records (in Table2) that may not be needed. But it seems the only solution.

Answer 2

First try the locate function to make sure both fields are there. Make a parameter equal to the field if found and boolean true else update or insert new field with the value of the other one. After that you know the entry exists and you can join the fields...or you can use try except finally to first try and execute the statement except if the field is not found then finally create new entry. Put all of that in a repeat until and make sure the until statement uses locate on both tables to see if its found.