Release object into a function - Memory Leak

Question

I am starting in the world Datasnap and I came across a situation that I can not find solution.

My code is on memory Leak, because I can’t release the objects. if I release the objects the access error violated in result.

function TServerMethods1.Teste(Key: string; ID: Integer): TFDJSONDataSets;
var
  Con  : TFDConnection;
  qry  : TFDQuery;
begin

   Con:= TFDConnection.Create(nil);
   qry:= TFDQuery.Create(nil);

    try
      qry.Connection:= Con;

      qry.SQL.Text:= Format('select id, nome from clientes where id = %d', [ID]);
      qry.Open;

      Result:= TFDJSONDataSets.Create;
      TFDJSONDataSetsWriter.ListAdd(Result, qry);

    finally
      FreeAndNil(qry);
      FreeAndNil(Con);
    end;
end;

i need to release the created objects [qry, con] but I’m not getting it.

Answer 1

The TFDJSONDataSets returns the result of qry which is passed by reference. So you can’t destroy it while the Result not delivered.

How to solve?

vDataSetX := TServerMethods1.Teste('stringX', integerX);
...
  usa o vDataSetX como precisar
...
vDataSetX .Close;
vDataSetX .Free;
vDataSetX  := Nil;

How was passed by reference to the Close, Free will terminate the connection, and the Nil will release from memory the vDataSetX.

Answer 2

When it comes to Tfdquery, prefer to use . Release instead of .Free. The . Release calls, internally, some routines for data cleaning that Tfdquery calls while processing the request among other operations. If you call only the . Free, you may have memory leaks.

As a rule: See if the object has a Release method and use it. If not, use . Free.

Answer 3

Creating the query and connection with Owner(application) will not need to destroy to prevent leakage.

Or... assign another Wner to be destroyed periodically.