Retrieve output parameter from FireDac stored procedure - delphi

Question

I've this Stored Procedure defined within a Firebird Database:
create or alter procedure GET_MSG (
IDLNG smallint,
IDMSG integer)
returns (
MSG varchar(200) character set UTF8)
as
begin
IF (:IDMSG > 40000) THEN
BEGIN
IF (:IDLNG = 1) THEN
BEGIN
SELECT NOMBRE01 FROM XMSG2 WHERE ID_XMSG2 = :IDMSG INTO :MSG;
EXIT;
END
IF (:IDLNG = 2) THEN
BEGIN
SELECT NOMBRE02 FROM XMSG2 WHERE ID_XMSG2 = :IDMSG INTO :MSG;
EXIT;
END
END ELSE
BEGIN
IF (:IDLNG = 1) THEN
BEGIN
SELECT NOMBRE01 FROM XMSG WHERE ID_XMSG = :IDMSG INTO :MSG;
EXIT;
END
IF (:IDLNG = 2) THEN
BEGIN
SELECT NOMBRE02 FROM XMSG WHERE ID_XMSG = :IDMSG INTO :MSG;
EXIT;
END
END
end
and I use this code to call this Stored Procedure from Firedac :
SPGeneric.StoredProcName:= 'GET_MSG';
SPGeneric.FetchOptions.Items:= SPGeneric.FetchOptions.Items - [fiMeta];
SPGeneric.Prepare;
with SPGeneric.Params do begin
Clear;
with Add do begin
Name:= 'IDLNG';
ParamType:= ptInput;
DataType:= ftSmallint;
Value:= IdLan;
end;
with Add do begin
Name:= 'IDMSG';
ParamType:= ptInput;
DataType:= ftInteger;
Value:= Id;
end;
with Add do begin
Name:= 'MSG';
ParamType:= ptOutput;
DataType:= ftString;
Size:= 200;
end;
end;
SPGeneric.ExecProc;
result:= VarToStr(SPGeneric.Params[2].Value);
The problem is that when I call this code with correct parameters (checked within Firebird), the result is always null. Is there anything wrong with this code?. Thanks
This is the code that works ok:
SPGeneric.StoredProcName:= 'GET_MSG';
SPGeneric.FetchOptions.Items:= SPGeneric.FetchOptions.Items - [fiMeta];
SPGeneric.Params.Clear;
with SPGeneric.Params.Add do begin
Name:= 'IDLNG';
ParamType:= ptInput;
DataType:= ftSmallint;
end;
with SPGeneric.Params.Add do begin
Name:= 'IDMSG';
ParamType:= ptInput;
DataType:= ftInteger;
end;
with SPGeneric.Params.Add do begin
Name:= 'MSG';
ParamType:= ptOutput;
DataType:= ftWideString;
Size:= 200;
end;
SPGeneric.Prepare;
SPGeneric.Params[0].Value:= IdLan;
SPGeneric.Params[1].Value:= Id;
SPGeneric.ExecProc;
result:= VarToStr(SPGeneric.Params[2].Value);
call Prepare after filling the parameters.
assign the parameters values after call prepare.

Answer 1

From the documentation :
After Prepare is called, the application cannot change command parameter data types and sizes. Otherwise, during the next Execute / ExecSQL / ExecProc / Open call, an exception will be raised. It is recommended to setup parameters before the Prepare call.
Here you have elected to not autopopulate the parameter information with
SPGeneric.FetchOptions.Items:= SPGeneric.FetchOptions.Items - [fiMeta];
So, since you are manually defining the parameters you should do this before calling Prepare.