Deserializing Generic Classes

Robert Harris

Does anyone know if the following should work??

  jsonVal  := TJSONObject.ParseJsonValue(AList.Text);

  jsonDeSer := TJsonDeserializer.Create(@jsonVal);

  FGridData := jsonDeSer.Value<TZzyGridDroppedData<T>>;  // Problem line

The above fails to deserialize the class of <T> with an error raised 'invalid state'.

Thanks.

Eugene Balabuev (LMD)

In the following row:

FGridData := jsonDeSer.Value<TZzyGridDroppedData<T>>

what is "T"?

Robert Harris

Hi Eugene, In this case <T> is declared as:

  TZzyCustomGridData = class(TObject);

  [SkipAll]

  TZzyGridDroppedData<T: TZzyCustomGridData> = class

Thanks, Robert.

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Eugene Balabuev (LMD)

I've checked on the following example:

type

  TMy<T> = class

  private

    FX: T;

    FY: T;

  public

    property X: T read FX write FX;

    property Y: T read FY write FY;

  end;

procedure TForm2.Button1Click(Sender: TObject);

var

  my:  TMy<Integer>;

  xml: IXMLDocument;

  s:   TXmlSerializer;

begin

  my := TMy<Integer>.Create;

  xml         := TXMLDocument.Create(nil);

  xml.Options := xml.Options + [doNodeAutoIndent];

  xml.Active  := True;

  s := TXmlSerializer.Create(xml.Node);

  try

    s['My'].Value(my);

  finally

    s.Free;

  end;

  Memo1.Lines := xml.XML;

end;

And everything worked fine. So, I cannot reproduce the issue. Can you, please, isolate problematic code into small demo project and sent it to our support email?..

Robert Harris

Hi Eugene,

You example is quite different to mine and I find it difficult to make a comparison. I use the json serializer. Here is a snippet of my code:

  [SkipAll]

  TZzyCustomViewRecord = class

  private

    FCode: string;

    FId: Integer;

    FName: string;

    FRecId: string;

    FRecordIndex: Integer;

  public

    property Code: string read FCode write FCode;

    property Id: Integer read FId write FId;

    property Name: string read FName write FName;

    property RecId: string read FRecId write FRecId;

    property RecordIndex: Integer read FRecordIndex write FRecordIndex;

  end;

  [SkipAll]

  TZzyGridDroppedData<T: TZzyCustomViewRecord> = class

     public

     DataArray : array of T;

     Caption:String;

     View: String;

  end;

  TZzyGridDroppedData<T: TZzyCustomViewRecord> = class

      property Records: TZzyGridDroppedData<T> read FGridData;

  end;

I think you will find that if you try this you may get the error. I say may because I have had to remove all generics from my classes regarding the other issue I reported. At this point I have lost a lot of time so I need to proceed with what I have rather than going backwards. However, that being said, it would be really good to have an answer to this for future use. If I get the chance I wou

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Eugene Balabuev (LMD)

Unfortunately, I can't say anything without isolated compilable demo, as was requested before.

Robert Harris

Hi Eugene,

If it;s okay with you I would like to keep this ticket open. I will send you a demo of my issue within the next 2 weeks. 

Thanks for your help.

Robert.

Eugene Balabuev (LMD)

Ok. No problems.