Delete all records from a MemDataset (like EmptyDataset)?
lazarus / 16-Databases

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tatamata · 2009-09-16 07:58

Since there is no EmptyDataset method for TMemDataset, I use
MemDataset1.First;
while not MemDataset1.EOF do begin;
  MemDataset1.Delete;
End;

But, this is incredibly slow for large datasets.
Is there any workaround how to delete all records from a MemDataset?

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tatamata · 2009-09-18 18:48

I have found solution myself:
Code: [Select]procedure EmptyMemDataSet(DataSet:TMemDataSet);

var

  vTemporaryMemDataSet:TMemDataSet;

  vFieldDef:TFieldDef;

  I:Integer;

begin

  try

    //Create temporary MemDataSet

    vTemporaryMemDataSet:=TMemDataSet.Create(nil);

    //Store FieldDefs to Temporary MemDataSet

    for I:=0 to DataSet.FieldDefs.Count-1 do begin

      vFieldDef:=vTemporaryMemDataSet.FieldDefs.AddFieldDef;

      with DataSet.FieldDefs[I] do begin

        vFieldDef.Name:=Name;

        vFieldDef.DataType:=DataType;

        vFieldDef.Size:=Size;

        vFieldDef.Required:=Required;

      end;

    end;

    //Clear existing fielddefs

    DataSet.Clear;

    //Restore fielddefs

    DataSet.FieldDefs:=vTemporaryMemDataSet.FieldDefs;

    DataSet.Active:=True;

  finally

  vTemporaryMemDataSet.Clear;

  vTemporaryMemDataSet.Free;

  end;

end;

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vladvons · 2013-10-08 18:02

to clear all records except fields clearing use
MemDataSet.Clear(false);

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Dibo · 2013-10-08 21:01

Or just MemDataset.Close and MemDataset.Open?

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vladvons · 2013-10-09 05:41

No.
calling Open() after Close() dosnt remove records from MemDataset