Can I serialize an interface(_recordset) with TJSONMarshal?

Question

I'm trying to serialize objects with TJSONMarshal (XE4) but I have a problem when objects has interfaces properties like _recordset

e.g.

My class:

  TFoo = class
  private
    FrsFoo: _recordset;
    FFooProp: integer;
  published
    property rsFoo: _recordset read FrsFoo write FrsFoo;
    property FooProp: integer read FFooProp write FFooProp;
  end;

My function:

function TestSerialize: string;
var
  JsonMarshal: TJSONMarshal;
  Foo: TFoo;
begin
  JsonMarshal := TJSONMarshal.Create(TJSONConverter.Create);
  Foo := TFoo.Create;
  Result := JsonMarshal.Marshal(Foo).ToString;
end;

It results:

{"type":"uTest.TFoo","id":1,"fields":{"FFooProp":0}}

rsFoo isn't serialized!

Can I serialize it? or its a limitation of TJSONMarshal?

Answer 1

In my case I just want to serialize _recordsets so my solution was:

1) Get all _Recordset type fields:

function Test.GetRecordsetFieldsFromObject(
  AObject: TObject): TStringList;
var
  Obj: TRttiType;
  Rtti: TRTTIContext;
  ObjField: TRttiField;
  IntfObj: IInterface;
  rsOut: _recordset;
begin
  Result := TStringList.Create;
  Obj := Rtti.GetType(AObject.ClassType);
  for ObjField in Obj.GetFields do
    if ObjField.FieldType.TypeKind = tkInterface then
    begin
      IntfObj := ObjField.GetValue(AObject).AsInterface;
      if IntfObj.QueryInterface(_Recordset, rsOut) = 0 then
      begin
        Result.Add(ObjField.Name);
        rsOut := nil;
      end;
    end;
end;

2) Register converter and reverter for each field founded

  for FieldName in FieldNameList do
  begin
    JsonMarshal.RegisterConverter(TFoo, FieldName, function(Data: TObject; Field: String): TListOfStrings
    var
      Obj: TRttiType;
      ObjField: TRttiField;
      rsProp: _Recordset;
      strStream: TStringStream;
    begin
      SetLength(Result, 1);
      strStream := TStringStream.Create;
      try
        Obj := Rtti.GetType(data.ClassType);
        ObjField := Obj.GetField(Field);
        rsProp := ObjField.GetValue(Data).AsInterface as _Recordset;
        rsProp.Save(TStreamAdapter.Create(strStream) as IUnknown, adPersistXML);
        Result[0] := strStream.DataString;
      finally
        rsProp := nil;
        strStream.Free;
      end;
    end);

    JsonUnMarshal.RegisterReverter(TFoo, FieldName, procedure(Data: TObject; Field: String; Args: TListOfStrings)
    var
      Obj: TRttiType;
      ObjField: TRttiField;
      rsProp: _Recordset;
      strStream: TStringStream;
    begin
      rsProp := coRecordset.Create;
      strStream := TStringStream.Create(Args[0]);
      try
        Obj := Rtti.GetType(data.ClassType);
        ObjField := Obj.GetField(Field);
        strStream.Position := 0;
        rsProp.Open(TStreamAdapter.Create(strStream) as IUnknown, EmptyParam, adOpenUnspecified, adLockUnspecified, 0);
        ObjField.SetValue(Data, TValue.From<_Recordset>(rsProp));
      finally
        rsProp := nil;
        strStream.Free;
      end;
    end);
  end;