TDAMemDataTable: Advanced record filtering (Delphi)

Overview

TDAMemDataTable is a class that holds live data on the client application at runtime, to make it available to application code and visual controls. TDAMemDataTable can be filled from a remote source (typically a Data Abstract server) using a Remote Data Adapter component that coordinates the connection to the server; it maintains a local history of changes (Delta) and can apply those changes back to the database, again using the Remote Data Adapter.

TDAMemDataTable allows to do filtering in two ways:

Standard filtering

  • Filter property allows to specify an conditional expression as a string. After specifying Filter value set Filtered property to True to activate the filter, e.g:
DAMemDataTable1.Filter := '(OrderID > 10) AND (OrderID < 30)';
DAMemDataTable1.Filtered := True;

procedure TForm1.DAMemDataTable1FilterRecord(DataTable: TDADataTable; var Accept: Boolean)
var
  lValue: Integer;
begin
  lValue := DataTable.FieldByName('OrderID').AsInteger;
  Accept := (lValue > 10) or (lValue < 30);
end;

procedure TForm1.FilterClick(Sender: TObject);
begin
  DAMemDataTable1.OnFilterRecord := DAMemDataTable1FilterRecord;
  DAMemDataTable1.Filtered := True;
end;

Filtering by a range

When datatable is sorted using the field list, then application may apply filtering by a field values range. This is most effective way to limit records, as it is using the datatable internal index structures.

The following methods control the filtering:

  • SetRangeStart - indicates that subsequent assignments to field values specify the start of the range of rows to include in the datatable;
  • EditRangeStart - enables changing the starting value for an existing range;
  • SetRangeEnd - indicates that subsequent assignments to field values specify the end of the range of rows to include in the datatable;
  • EditRangeEnd - enables changing the ending value for an existing range;
  • ApplyRange - applies a range to the datatable after setting of starting and ending values;
  • SetRange - sets the starting and ending values of a range and applies them;
  • CancelRange - removes any ranges currently in effect for the datatable;
DAMemDataTable1.SetRangeStart;
DAMemDataTable1.FieldByName('OrderID').AsInteger := 1001;
DAMemDataTable1.SetRangeEnd;
DAMemDataTable1.FieldByName('OrderID').AsInteger := 1051;
DAMemDataTable1.ApplyRange;
..
DAMemDataTable1.CancelRange;

is equal to

DAMemDataTable1.IndexFieldNames := 'OrderID';
DAMemDataTable1.SetRange([1001], [1051]);
..
DAMemDataTable1.CancelRange;

See also