DBLookupComboBox exception
lazarus / 16-Databases

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Old Dog · 2011-03-08 04:20

using lazarus 0.9.28.2 fpc 2.2.4

have a dbf table of states with abbreviation, statename, etc

have dbf table of vendors with vendorstate (abbreviation stored) , etc

have vendor form with grid and dblookupcombo for state

using object explorer:
set listsource to dsstate
     listfield     to statename
     keyfield     to abbreviation
     datasource to dsvendor
     datafield     to vendorstate

when vendor table is created (no records) get exception can't convert
null to string

if I create a record and place a valid abbreviation value in
vendorstate, no exception.  DBLookupComboBox works as expected

any ideas on why and a work around?

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Old Dog · 2011-03-08 23:13

seems I was a little hasty in saying things worked fine.  get the same
exception when I attempt to add new record to table.

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Old Dog · 2011-03-09 19:59

It seems that the problem exists because the DataField, VendorsState,
is empty when a new record is created, either by append or by creation
of the DBF file.  Is there a way to initial a field?

I can make the exception go away by leaving the DataField property
empty in the object explorer, but then it doesn't do me any good
either.

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jesusr · 2011-03-11 21:06

please try with a newer lazarus revision, for example any snapshot of
lazaus fixes should be fine. If it still raises the exception, please
submit a bug report with a sample project.

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Old Dog · 2011-03-13 03:24

having had no luck in upgrading  FPC from 2.2.4 to 2.4.0 or 2.4.2, I
am not sure i can get a snapshot to work.  Nor do I have a clue how to
get one.

I have, however, found a partial solution.  Using the OnNewRecord
event of the DBF, I can set the DataField.text := 'XX' and avoid the
exception generated from append.   I assume a single space in the
quotes (' ') will also work but have not tested it yet.


This does not solve the problem when a new file is created, or an
empty file is opened.