TDataset and TMemDataset

Question

I need to iterate through a number of MySQL queries and save them in an array of TMemDataset's. This seems to do it:

MemDataset1.CopyFromDataset(ZQuery1,True); 

However each time the query changes, all the previous TMemDataset's are changed to contain the new values (I guess because they are "data-aware components"). If I get rid of ZQuery1 with ZQuery1.Free, then all of the data vanishes. How do I avoid this?

I am using FreePascal, but I bet the solution for Delphi would apply too.

Answer 1

The solution is to have an array of ZQuery as well as an array of MemDataSet

type
  TZQueries = array of TZQuery;
  TMemDataSets = array of TMemDataset;

procedure Test;
var
  ZQueries: TZQueries;
  MemDatasets: TMemDatasets;
  i: integer;
begin
  try
    SetLength(ZQueries,10);
    SetLength(MemDatasets,10);
    for i:= Low(ZQueries) to high(ZQueries) do begin
      ZQueries[i]:= TZQuery.Create;
      ZQueries[i].Connection:= ZConnection1;
      ZQueries[i].SQL.Text:= QueryTextFromSomewhere
    end; {for i} 
    for i:= Low(MemDatasets) to High(MemDatasets) do begin
      MemDatasets[i]:= TMemDataset.Create;
      ZQueries[i].Open;
      MemDatasets[i].CopyFromDataset(ZQueries[i],True);
    end; {for i}
    ....
      code to process the memdatasets
    ....
  finally
    for i = Low(ZQueries) to High(ZQueries) do begin
      ZQueries[i].Free;
    end; {for i}
    for i = Low(MemDatasets) to High(MemDatasets) do begin
      MemDatasets[i].Free;
    end; {for i}
  end; {tryf}
end;

Something like that should work, because now there's no more confusion between the Queries and the memdatasets.