Zeoslib - loop over calculated fields

Question

I have a Delphi 7 project using Zeoslib 6.6.6 and Sqlite3. On the form I have a Zquery selecting everything out of a sample database table along with a bunch of calcuated fields (TFloatField; TCurrencyField). The OnCalcFields event of the query runs fine and all field values are set. However, when i try to loop over the dataset, I consistently get a 'List index out of bounds (62893)' exception, though i am well within the field count limit (the first calculated field of about 14).

Snippet: gd is a TStringGrid, ZQuery4 is a TZQuery

while not ZQuery4.Eof do
begin
   row := row + 1;
   gd.Cells[0, row] := IntToStr(gd.Row);
   gd.Cells[1, row] := ZQuery4pid.Value; //Known column
   gd.Cells[2, row] := FormatFloat('0.00', ZQuery4area.Value); //known column

   for i := 3 to ZQuery4.FieldCount - 1 do
   begin
     field := Zquery4.Fields[i]; //crashes here when accessing the first calculated field.

     if field.IsNull
       then gd.Cells[i, row] := ''
       else gd.Cells[i, row] := field.AsString;
   end;
end;

The bizarre thing is that if i connect a DBGrid to the query it works fine. Any ideas?

I'd examine the call stack when you get the index out of bounds. It may not be the `i` that's casuing it, but an index used somewhere in the code behind it... (looping through the dataset like that will cause the dataset's events to fire!) — Marjan Venema, Jul 17 '11 at 11:11

score 0 · Answer 1 · answered Jul 18 '11 at 01:18

What happens when gd.cells[x,row] exceeds the number of rows you have set in the string grid? Probably that's your error. If you set your stringgrid to have 62000 rows, great, that's your error. Otherwise, I suspect that you're hitting a limit.

I always used to have my string grid row count grow like this, with logic after row=row+1:

  if gd.RowCount<=row then gd.RowCount := row+1;

If however you really are getting this error at 60k+ stringgrid rows, it is possible that instead what is happening is you are hitting a string grid row length limit.

Since you haven't obviously posted ALL your code, it's hard to know what sets the row count in the string grid where, and how it grows.

In the case that you've hit a limit beyond which a StringGrid no longer operates, I suggest you drop StringGrid and use ExgridView or some other virtual gridview that can handle a very very large amount of data.

score 0 · Answer 2 · answered Jul 19 '11 at 09:40

0

I seem to have stumbled across at least a workaround: changing

gd.Cells[i, row] := field.AsString;

to

gd.Cells[i, row] := field.DisplayText;

seems to have solved the problem.

answered Jul 19 '11 at 09:40

Andrew

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Zeoslib - loop over calculated fields

2 Answers2