TOracleDataset composite look up key fields

[Petros Amiridis]

Hi,

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[Marco Kalter]

Does this work with other datasets? It seems that the lookup field tries to determine the value of the KeyFields as if it just one field. I think this is all handled at the TDataSet and TField level (DB.pas), so I wonder how this works with other TDataSet descendants.

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Marco Kalter
Allround Automations

 

[Petros Amiridis]

Hi,

The Delphi Help topic "Defining Look Up Fields" has this step for the KeyFields property:

6. Choose from the Key Fields drop-down list a field in the current dataset for which to match values. To match more than one field, enter field names directly instead of choosing from the drop-down list. Separate multiple field names with semicolons.

So I do this but it does not work. In TTable it works, and this is a TDataSet descendant.

I wonder if any other developers ever tried to do a look up with a composite primary key. Did it work for you?

Please check this out? I can't imagine that lookup's cannot be done when the primary key is a composite one.

Originally posted by mkalter:
Does this work with other datasets? It seems that the lookup field tries to determine the value of the KeyFields as if it just one field. I think this is all handled at the TDataSet and TField level (DB.pas), so I wonder how this works with other TDataSet descendants.

 

[Marco Kalter]

Did I write KeyFields? I meant to write LookupKeyFields

. A composite primary key is no problem, a composite lookup value just might be.

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Marco Kalter
Allround Automations

 

[Petros Amiridis]

A composite primary key is no problem, a composite lookup value just might be.

But... how can you have a composite KeyFields without having the same LookUpKeyFields. If I have a table that has a foreign key to a lookup table with a composite primary key (ex. ID1 and ID2), then I need to set up the KeyFields as 'ID1;ID2' and the LookupKeyFields as 'ID1;ID2'... isn't this the case? If it is, this doesn't work with TOracleDataset. If you agree on this (i.e. that it doesn't work) then please tell me, so I can stop using composite keys and convert all the primary keys to single column ones.

Thank you

[This message has been edited by amiridis (edited 08 February 2001).]

 

[Marco Kalter]

I tried this, and the lookup feature seems to work okay. As soon as I use the lookup as a combobox in a dbgrid, the error you mentioned occurs. I traced this down to dbgrids.pas where it says:

if FieldKind = fkLookup then
begin
  MasterField := Dataset.FieldByName(KeyFields);
  ...
end

I wonder how this can ever work for compound keys, since this can never return a single MasterField...

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Marco Kalter
Allround Automations