Luis,

I've looked quite hard at your problem (as originally posted) and I think
you have your master-detail relationships back-to-front for doing what you
ask to do.

I think DatasetC is, for your requirements, the detail dataset of an
optional master-detail relationship. I believe what you want to do with
the three datasets can be done quite simply by swapping the Mastersource
and MasterParamLinks between DatasetA and DatasetB as alternative
masters. Don't use a table component for DatasetC, use a query:

SELECT idC, A, B, ....
from TableC
where A = :ParamA
and B = :ParamB

When DatasetA is the master, ParamA is the MasterParamLink to DatasetA.idA
and ParamB gets its value from DatasetB.idB; and when DatasetB is the
master, ParamB MasterParamLinks to DatasetB.idB and ParamA gets its value
from DatasetA.idA.


regards,
Helen Borrie (TeamIBO Support)

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