Zeoslib Portal

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    ...
    { Creates an SQL statement and resultsets }
    if not FUseCurrentStatment then
      if FSQL.StatementCount> 0 then
        ResultSet := CreateResultSet(FSQL.Statements[0].SQL, -1)  // LOAD ALL RECORDS (memory consumption pops to max)

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function TZAbstractRODataset.CreateResultSet(const SQL: string;  MaxRows: Integer): IZResultSet;

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    if MaxRows > 0 then
      Statement.SetMaxRows(MaxRows);
  ...
      Result := Statement.ExecuteQueryPrepared; // after execution  memory consumption pops to max

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procedure TZAbstractRODataset.InternalOpen;
  ResultSet := CreateResultSet(FSQL.Statements[0].SQL, FetchRow)

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function TZAbstractRODataset.CreateResultSet(const SQL: string;
  MaxRows: Integer): IZResultSet;
  Result := Statement.ExecuteQueryPrepared;

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function TZPostgreSQLCAPIPreparedStatement.ExecuteQueryPrepared: IZResultSet;
  QueryHandle := ExectuteInternal(ASQL, SSQL, lcExecute);

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function TZPostgreSQLCAPIPreparedStatement.ExectuteInternal(const SQL: RawByteString;
  const LogSQL: String; const LoggingCategory: TZLoggingCategory): PZPostgreSQLResult;
  Result := FPlainDriver.ExecuteQuery(FConnectionHandle, PAnsiChar(SQL));

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function TZPostgreSQLBaseDriver.ExecuteQuery(
  Handle: PZPostgreSQLConnect; Query: PAnsiChar): PZPostgreSQLResult;
begin
  Result := POSTGRESQL_API.PQexec(Handle, Query); // load whole rowset
end;

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TZPOSTGRESQL_API = record
(
  PQexec:          TPQexec;

)
TPQexec          = function(Handle: PPGconn; Query: PAnsiChar): PPGresult; cdecl;

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function TZPostgreSQLStatement.SendQuery(const SQL: RawByteString): boolean;
var
  ConnectionHandle: PZPostgreSQLConnect;
begin
  Result := False;
  ConnectionHandle := GetConnectionHandle();
  ASQL := SQL; //Preprepares the SQL and Sets the AnsiSQL
  Result := FPlainDriver.SendQuery(ConnectionHandle, PAnsiChar(ASQL)) = 1;
  DriverManager.LogMessage(lcExecute, FPlainDriver.GetProtocol, LogSQL);
end;

function TZPostgreSQLStatement.SetSingleRowMode: Boolean;
begin
  Result := FPlainDriver.SetSingleRowMode(GetConnectionHandle) = 1;
end;

function TZPostgreSQLStatement.GetResultSet: IZResultSet;
begin
  Result := CreateResultSet(LogSQL, FPlainDriver.GetResult(GetConnectionHandle))
end;                                                                            

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procedure xxx;
var
query :TZQuery;
fld,tup: integer;
begin
    query := TZQuery.Create(self);
    query.Connection := ZConnection1;
    query.SQL.Clear;
    query.SQL.Add('select * from contracts where sk = :p1');
    query.Prepare;
    query.ParamByName('p1').Value := 400;
    query.OpenAsync;
    for fld := 0 to query.FieldCount - 1 do
        ShowMessage(query.Fields[fld].FieldName);

    query.First;
    ShowMessage(inttostr(query.RecordCount));
    while not query.eof do begin
        for fld := 0 to query.FieldCount - 1 do
          ShowMessage(query.Fields[fld].AsString);
        query.next;
    end;
end;

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procedure TZAbstractRODataset.OpenAsync;
begin
  if not Active then begin
    if Statement is TZPostgreSQLCAPIPreparedStatement then begin
        FOpenAsync := True;
        IsUniDirectional :=True;
    end;
    Open;
  end;
end;      

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procedure TZAbstractRODataset.InternalOpen;
var
  ColumnList: TObjectList;
  I: Integer;
begin  
...
      if FSQL.StatementCount> 0 then
        ResultSet := CreateResultSet(FSQL.Statements[0].SQL, -1)
      else
...
   if DefaultFields and not FRefreshInProgress then
    begin
      CreateFields;   
...
end;

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function TZAbstractRODataset.CreateResultSet(const SQL: string;
  MaxRows: Integer): IZResultSet;
begin
     ...
      if FOpenAsync then
        Result := Statement.ExecuteQueryPreparedAsync //<-- introduced by me
      else
        Result := Statement.ExecuteQueryPrepared;
     ...

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function TZPostgreSQLCAPIPreparedStatement.ExecuteQueryPreparedAsync: IZResultSet; // gapsf
begin
  if SendQueryPrepared then begin
    if SetSingleRowMode then // <-- here I silently force single row mode but should dont
      Result := GetResultSet // return only one (first) row, not whole rowset
    else
      Result := CreateResultSet(GetResultSet); // <-- maybe I wrong with CreateResultSet() since GetResultSet already have CreateResultSet
  end
  else
    Result := nil;
    inherited ExecuteQueryPreparedAsync;
end;

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type
  txview = class(TWinControl)
  private
    cursorname: string;
    datasource: tdatasource;
    query: TZReadOnlyQuery;
    ds : TbufDataSet;
    dbgrid : TDBGrid;
    allfetched : boolean;

...
implementation
...
procedure copyrecords(src, dst : TDataSet);
var
  fld : Integer;
  cr : TBookmark;
begin
    cr := dst.GetBookmark;
    src.DisableControls;
    dst.DisableControls;
    src.first;
    while not src.eof do begin
      dst.Append;
      for fld := 0 to src.FieldCount - 1 do
           dst.Fields[fld].Value := src.Fields[fld].Value;
      src.next;
    end;
    dst.GotoBookmark(cr);
    src.EnableControls;
    dst.EnableControls;
end;

procedure txview.fetch_view(DataSet: TDataSet);
begin
    if ds.Eof and not allfetched then begin
        ds.DisableControls;
        ds.BeforeScroll := nil;
        query.Refresh;
        if query.RecordCount > 0 then begin
            copyrecords(query,ds);
            ds.BeforeScroll := @fetch_view;
        end
        else begin
            allfetched := True;
            showmessage(inttostr(ds.RecordCount));
            query.SQL.Clear;
            query.SQL.Add('close '+cursorname);
            query.ExecSQL;

            query.SQL.Clear;
            query.SQL.Add('end');
            query.ExecSQL;
        end;
        ds.EnableControls;
        dbgrid.Refresh;
//        showmessage(inttostr(ds.RecordCount));
    end;
end;

procedure txview.update_view(conn: TZConnection; sql : string);
var
  fld : Integer;
  guid : TGuid;
begin
    qupdate := TZUpdateSQL.Create(self);
    query.UpdateObject := qupdate;
    query.Connection := conn;

    CreateGUID(guid);
    cursorname := StringReplace(GUIDToString(guid),'{','B',[]);
    cursorname := StringReplace(cursorname,'}','E',[]);
    cursorname := StringReplace(cursorname,'-','',[rfReplaceAll]);
    query.SQL.Clear;
    query.SQL.Add('begin');
    query.ExecSQL;

    query.SQL.Clear;
    query.SQL.Add('declare '+cursorname+' cursor for '+sql);
    query.ExecSQL;

    query.SQL.Clear;
    query.SQL.Add('fetch forward 100 in '+cursorname);
    query.Prepare;
    query.open;

    datasource.DataSet := query;
    dbgrid.DataSource := datasource;
    query.BeforeScroll := @fetch_view;
    dbgrid.Parent := self;
end;