为什么我的Delphi过滤器不起作用？

Question

test := TFDMemTable.Create(nil);
test.CopyDataSet(TempUnplannedDemand, [coStructure, coRestart, coAppend]);
test.First;
    while not test.Eof do
    begin
      ShowMessage(DateTimeToStr(test.FieldByName('demand_date').AsDateTime) +
                ' - ' +
                IntToStr(test.FieldByName('level').AsInteger));
      test.Next;
    end;

将显示
24/03/2017 - 1
24/03/2017 - 0
24/03/2017 - 1
24/03/2017 - 1

  test.IndexFieldNames := 'level';

  //test.SetRangeStart;
  //test.FieldByName('level').AsInteger := 0;
  //test.SetRangeEnd;
  //test.FieldByName('level').AsInteger := 0;
  //test.ApplyRange;

  //test.SetRange([0],[0]);

  test.Filter := 'level=0';
  test.Filtered := True;

  test.First;
  while not test.Eof do
  begin
      ShowMessage(DateTimeToStr(test.FieldByName('demand_date').AsDateTime) +
                ' - ' +
                IntToStr(test.FieldByName('level').AsInteger));
      test.Next;
    end;

将显示
24/03/2017 - 1
24/03/2017 - 0
24/03/2017 - 1
24/03/2017 - 1

为什么test.Filter:='level = 0'; 不工作

test.Filter:='level = 0'对不起的结果是RecCount = 0.

test.Filter:='level = 1'=> RecCount = 3
test.Filter:='level <> 1'=> RecCount = 1

Answer 1

我认为你的问题必须在于你没有包含在你的q中.以下工作正常并产生Level = 0和Level = 1的预期结果.Test数据集的字段ID = ftInteger,Demand_Date = ftDateTime和Level = ftInteger并TDBGrid通过以下方式连接到a TDataSource:

procedure TForm1.FormCreate(Sender: TObject);
begin
  Test.CreateDataSet;
  Test.InsertRecord([1, '24/03/2017', 0]);
  Test.InsertRecord([2, '24/03/2017', 1]);
  Test.InsertRecord([3, '24/03/2017', 0]);
  Test.InsertRecord([4, '24/03/2017', 1]);
  Test.InsertRecord([5, '24/03/2017']);  //  <- this leaves the Level column as Null

  Test.IndexFieldNames := 'Level';
end;

procedure TForm1.ApplyFilter;
begin
  Test.Filtered := False;
  Test.Filter := 'Level=0';  //  or 'Level=1'
  Test.Filtered := True;
end;

注意ID = 5的数据行; 这不包含Level列的值,FireDAC因此将其视为包含Null值,因此,该行将不会包含在已过滤的重新设置中,无论Level是否指定为1或0,因为Null不匹配这些.

顺便说一下,一个空的ftInteger列将返回0作为其AsInteger值,因此将返回一个ftString值.