mORMot Open Source

BostjanZ

Member

Registered: 2016-11-05

Posts: 7

TDynArray.SaveToJSON bug ?

Hi,

I have found some strange behaviour with TDynArray conversion to JSON (or maybe I am missing something).

If I define array of record which has only integer fields in definition, conversion to JSON fails, but if I add an string to record everything works as expected.

I use XE6 and tested it also with 10.2 CE (both 32bit) and results were the same, I used lastest nightlybuild of mORMot for test.

Definition for array is as such:

type
  TPosition = packed record
    FieldId:integer;
    Width: integer;
//    DummyString:string;
  end;

type TPositions = array of TPosition;

In the following procedure content of TmpJSON is used as conversion target and I have added results in comments:

procedure TForm1.Button1Click(Sender: TObject);
var fPositions:TPositions;
    DAPositions: TDynArray;
    TmpPos:TPosition;
    TmpJSON:RawUTF8;
begin
  DAPositions.Init(TypeInfo(TPositions),fPositions);
  DAPositions.Clear;
  TmpPos.FieldId:=1;
  TmpPos.Width:=50;
  //test if record to JSON is ok
  TmpJSON:=RecordSaveJSON(TmpPos, typeInfo(TPosition));
  //OK we get TmpJSON='{"FieldId":1,"Width":50}'
  DAPositions.Add(TmpPos);
  TmpPos.FieldId:=2;
  TmpPos.Width:=150;
  DAPositions.Add(TmpPos);
  //test if array to JSON is ok
  TmpJSON:=DAPositions.SaveToJSON;
  //ERROR: we get TmpJSON='[214748364801,644245094402]'
  //
  //if we add DummyString:string; to TPosition definition
  //we get correct data: TmpJSON='[{"FieldId":1,"Width":50,"DummyString":""},{"FieldId":2,"Width":150,"DummyString":""}]'
end;

Kind regards,
Bostjan

ab

Administrator

From: France

Registered: 2010-06-21

Posts: 14,242

Website

Re: TDynArray.SaveToJSON bug ?

It is a Delphi/FPC limitation: a record without any managed field has not sufficient RTTI.

You need to register the record as text first, using TTextWriter.RegisterCustomJSONSerializerFromText().

BostjanZ

Member

Registered: 2016-11-05

Posts: 7

Re: TDynArray.SaveToJSON bug ?

Thank you for your answer !

I solved my problem by changing record definiton, but since it was a simple case and I already wanted to try how custom serializer works, based on GutHub example (section 10.1.3.2.4. Text-based definition from SAD), I added this before SaveToJSON:

  TTextWriter.RegisterCustomJSONSerializerFromText(TypeInfo(TPosition),'FieldId integer Width integer');
  TmpJSON:=DAPositions.SaveToJSON();

but results were the same: [214748364801,644245094402].

I also tried:

'{FieldId integer Width integer}'; //error with registering

and

'A: record FieldId, Width: integer;'; //result: '[214748364801,644245094402]'

Is it required to register record (TPosition) or array serialization (TPositions) ?

ab

Administrator

From: France

Registered: 2010-06-21

Posts: 14,242

Website

Re: TDynArray.SaveToJSON bug ?

Try with TypeInfo(TPositions)