TBlobField.IsBlob Method

Indicates that this is a BLOB field.

Pascal

class function IsBlob: Boolean; override;

C++

virtual __fastcall Boolean IsBlob();

Description

Use IsBlob when working with a TField object to determine whether it represents BLOB data. For example, before using the GetData or SetData method (which does not work with BLOB fields), call IsBlob to determine whether the method can be used. The IsBlob method for TBlobField always returns true.

C++ Examples:

Copy Code

/*
This example requires a button, a test edit, and a populated
ClientDataSet.  Pipe the ClientDataSet through a DataSource
to a DGGrid or DBNavigator to control the current field.
Cast the data correctly according to the field type when
assigning to the test edit.
*/
void __fastcall TForm1::Button1Click(TObject *Sender)
{
  // Retrieve the "raw" data from Field1
  if (!CDS->Fields->Fields[0]->IsBlob()) // __classid(TField) GetData does not work for BLOB fields
  {
    void *MyBuffer = malloc(CDS->Fields->Fields[0]->DataSize);
    try
    {
      if (!CDS->Fields->Fields[0]->GetData(MyBuffer))
        MessageDlg(CDS->Fields->Fields[0]->DisplayName + "is blank.", mtInformation, TMsgDlgButtons() << mbOK,0);
      else
        // Do something with the data;
        Edit1->Text = reinterpret_cast<char *>(MyBuffer); // for a stringfield
    }
    __finally
    {
      free(MyBuffer);
    }
  }
}

void __fastcall TForm1::FormCreate(TObject *Sender)
{
  CDS->LoadFromFile("../CDS.XML");
}

Delphi Examples:

Copy Code

{
This example requires a button, a test edit, and a populated
ClientDataSet.  Pipe the ClientDataSet through a DataSource
to a DGGrid or DBNavigator to control the current field.
Cast the data correctly according to the field type when
assigning to the test edit.
}

{$IFNDEF UNICODE}
uses SwSystem;
{$ENDIF}

procedure TForm1.Button1Click(Sender: TObject);
var MyBuffer: Pointer;
begin
{ Retrieve the "raw" data from Field1 }
with CDS.Fields[0] do
  begin
    if not IsBlob then { this does not work for BLOB fields }
    begin
      { Allocate space }
      MyBuffer:= GetMemory(DataSize);
      try
        if not GetData(MyBuffer) then
          MessageDlg(DisplayName + ' is NULL', mtInformation, [mbOK], 0)
        else
          { Do something with the data };
          Edit1.Text:= string(PAnsiChar(MyBuffer)); // for a stringfield
      finally
        { Free the space }
        FreeMem(MyBuffer, DataSize);
      end;
    end;
  end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
{$IFDEF UNICODE}
  CDS.LoadFromFile(GetCurrentDir + '\CDS.XML');
{$ELSE}
  CDS.LoadFromFile(gsAppPath + 'CDS.XML');
{$ENDIF}
end;