[Lazarus] need suggestion about TDataset.Lookup

[FreeMan]

hi,
I need use TDataset.Lookup, I know how to do this, but need help about, 
result field is blob field
Var
  V : Variant;
BlobField : TBlobField;
..
V := QUE_.Lookup('UNQ_ID', H_ID, 'BIN_DATA');// BIN_DATA type is TBlobField
if V=Null then Exit;
   BlobField := TBlobField(V);//<- Problem is here !!!

//  if QUE_.Locate('UNQ_ID', VarArrayOf([H_ID]), [])
//   then BlobField := TBlobField(QUE_.FieldByName('BIN_DATA'))
//   else Exit;

I'm looking for fast way