How to delete all records matching a certain value in a FireDAC dataset?

Question

I have a usual while not EOF do loop that deletes certain records from a memory table. Deleting the last record does not signal EOF as expected. Here's my code:

mtCt.First;  
while Not mtCt.Eof do  
begin  
  if mtCtAmt.Value = 0.0 then
    mtCt.Delete
  else
    mtCt.Next;  
end;

How can I delete all records matching a certain value in a FireDAC dataset?

Answer 1

This is normal behavior with all Delphi datasets.

If your deleting logic is as simple as your example, you can simply ignore this, anyway the next iteration will not satisfy the deleting condition, issuing a Next and going EOF.

If instead the logic is complex and you need to avoid the unnecessary iteration, you may use a trick like this:

var
  PrevRecNo: Integer;
begin
  mtCt.First;  
  while Not mtCt.Eof do  
  begin  
    if mtCtAmt.Value = 0.0 then
    begin
      // save the current record number 
      PrevRecNo := mtCt.RecNo;

      // delete will normally not change current record number
      // unless you've deleted the last record, in this case
      // the current record will be one less than before
      mtCt.Delete;

      // so, if the saved record number and the current one are
      // different, you've delete the last record, just issue a
      // Next in order to hit EOF and exit the while loop
      if mtCt.RecNo <> PrevRecNo then
        mtCt.Next;
    end
    else
      mtCt.Next;  
  end;