• Firebird queries must be prepared before they are executed. By using parameters, the query can be prepared once and executed many times.
• It is the only way (besides direct API calls or using table components[slow]) to write blobs to the table.
• It allows stored procedures to recieve and return parameters

Insert into "DAMAGE" ( "SPEC_NUM", "WHEN_CALC" ) VALUES ( :SPEC_NUM,  :WHEN_CALC )

procedure TxxDataSet.StringPut(Field, A_Value: string);
begin
  with Params.CreateParam(ftString, Field, ptInput) do
    AsString := A_Value;
end;

procedure TxxDataSet.FloatPut(Field: string; A_Value: Double);
begin
  with Params.CreateParam(ftFloat, Field, ptInput) do
    AsFloat := A_Value;
end;

procedure TxxDataSet.IntegerPut(Field: string; A_Value: integer);
begin
  with Params.CreateParam(ftInteger, Field, ptInput) do
    AsInteger := A_Value;
end;

procedure TxxDataSet.MemoSave(Field: string;
   AnArray: pointer; n: integer);
begin
  with Params.CreateParam(ftBlob, Field, ptInput) do
    SetBlobData(AnArray, n);
end;

procedure TxxDataSet.IntegerPut(Field: string; A_Value: integer);
begin
  try
    Params.ParamByName(Field).AsInteger := A_Value;
  except
    on EDatabaseError do 
      with Params.CreateParam(ftInteger, Field, ptInput) do
        AsInteger := A_Value;
  end;
end;

  self.Close;
  self.ParamCheck := True;     // If false, the parameters are not used
  self.SQL.Text   := 'Insert into "tablename" ...';
  self.ExecSQL;                // Used to modify the table
  self.SQL.Text   := 'commit'; // Clears the Parms list and 
  self.ExecSQL;                //   lets other users see the changes 

xsqlda index out of range

Note:

In methods, I frequently use self (which is never required) because it tells the IDE to display a list of properties and methods after you type the period. (Use Ctrl-Space to display the list if the period is already typed.)

procedure TxxDataSet.StringPut(Field, value: string);
begin
  with Params.CreateParam(ftString, Field, ptInput) do
    AsString := value;
end;

• In the debugger, value had the string passed to it
• However, since value is also a TParam property, it was null in the assignment statement

URL: http:// cpcug.org / user / clemenzi / technical / Databases / Delphi / QueryParameters.html