[SOLVED] dbf and deleting records in a loop
lazarus / 16-Databases

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timcs · 2013-01-03 21:47

Below is my code where I am trying to delete records from a dbf where
the date in each record is not today please can some point out where I
am going wrong as when I run this, it only appears to be deleting some
of the records and each time I click the button that runs this, it
does some more BUT even deletes todays record!

Code: [Select]if dbf1.active = true then
      begin
         // dbf1.Filtered:=true;
           dbf1.IndexName:='';
           prev := 1;
           dbf1.Filtered:=true;

           dbf1.DisableControls;
           if dbf1.ExactRecordCount>0 then
           begin

               dbf1.Filtered:=false;
               dbf1.Active:=false;
               dbf1.Active:=true;
               dbf1.First;
               while not dbf1.EOF do
               begin
                  if
DateOf(dbf1.FieldByName('dateon').AsDateTime)<DateOf(now) then
                     dbf1.Delete;

                  dbf1.Next;

                end;

             dbf1.TryExclusive;

             dbf1.PackTable;
             dbf1.EndExclusive;

           dbf1.Filtered:=false;

           dbf1.Active:=false;
           dbf1.Active:=true;
           dbf1.EnableControls;
           dbf1.first;


           prev := 0;
         end;                        

the variable prev is set to trigger the required filter in the
OnFilterRecord procedure :

Code: [Select]if prev = 1 then
   begin
   accept :=
(DateOf(Dataset.FieldByName('dateon').AsDateTime)<DateOf(now));

   end;

Any Ideas please, I thought this would work but it appears not to

Thanks

TimCS

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ttomas · 2013-01-04 00:16

Code: [Select]               
if DateOf(dbf1.FieldByName('dateon').AsDateTime)<DateOf(now) then
  dbf1.Delete
else
  dbf1.Next;

When you delete record your cursor is moved to next record and with
next dbf1.Next you skip next record

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timcs · 2013-01-04 00:25

Quote from: ttomas on January 04, 2013, 01:16:40 amCode: [Select]    
         
if DateOf(dbf1.FieldByName('dateon').AsDateTime)<DateOf(now) then
  dbf1.Delete
else
  dbf1.Next;

When you delete record your cursor is moved to next record and with
next dbf1.Next you skip next record

Hi ttomas thanks for your reply such a simple piece of logic sometimes
I think I look at the code too long and too hard not seeing the
obvious !!!. I think I just had it in my head that it would move next
anyway but if that record match the if condition it would delete it
and then move to the next record to see if that matched etc..

Still if I move to the next record at the end of the loop why would it
skip a record before hitting the if condition ? the move next is
separate to the if condition not part of it. Sorry for the stupid
question, I think I have been doing too many other programming
languages at the same time 

Thanks

TimCS

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ttomas · 2013-01-04 00:38

Quote from: timcs on January 04, 2013, 01:25:21 amStill if I move to
the next record at the end of the loop why would it skip a record
before hitting the if condition ? the move next is separate to the if
condition not part of it.
dbf1.Delete - delete record and move to next record.
With your dbf1.Next your cursor is moved again and skip 1 record
(record after deleted record).
Put DBGrid and look for your cursor when you delete record.

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timcs · 2013-01-04 09:44

Quote from: ttomas on January 04, 2013, 01:38:21 amQuote from: timcs
on January 04, 2013, 01:25:21 amStill if I move to the next record at
the end of the loop why would it skip a record before hitting the if
condition ? the move next is separate to the if condition not part of
it.
dbf1.Delete - delete record and move to next record.
With your dbf1.Next your cursor is moved again and skip 1 record
(record after deleted record).
Put DBGrid and look for your cursor when you delete record.

That now makes sense I did not release the delete did that , thanks
ttomas

TimCS