Popular Clientdataset with JSON truncates the data in 255 characters

Question

I am trying to pass a JSON to a Tclientdataset using the following function:

procedure JsonToDataset(aDataset : TDataSet; aJSON : string);
var
  JObj: TJSONObject;
  JArr: TJSONArray;
  vConv : TCustomJSONDataSetAdapter;
  i: Integer;
begin
  if (aJSON = EmptyStr) then
  begin
    Exit;
  end;

  JArr := nil;
  JObj := nil;

  try
    JArr := TJSONObject.ParseJSONValue(aJSON) as TJSONArray;
  except
    JObj := TJSONObject.ParseJSONValue(aJSON) as TJSONObject;
  end;

  vConv := TCustomJSONDataSetAdapter.Create(Nil);

  try
    vConv.Dataset := aDataset;

    if JObj <> nil then
      vConv.UpdateDataSet(JObj)
    else
      vConv.UpdateDataSet(JArr);

  finally
    vConv.Free;
    JObj.Free;
  end;
end;

However, when I have a large field, the function truncates my string in 255 characters. Example of JSON:

{
  "string": "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Curabitur rhoncus convallis risus, nec posuere nisl gravida vitae. Duis elementum augue nec condimentum rutrum. Aliquam sodales, dolor at laoreet pharetra, tortor eros efficitur eros, vel euismod sem nulla quis erat. Aliquam erat volutpat. Ut vitae congue lectus, et sodales velit. Cras suscipit pulvinar dolor ut consequat. Praesent eget pellentesque justo. In at maximus lectus, posuere mattis felis."
}

Is there any way around this problem?

Answer 1

The Class TCustomJSONDataSetAdapter identifies and creates the Field Type by default.

In the case of content string a field of the type will be created by default WideStrig 255-character.

Ideal is you create the field before the conversion with a size larger than the one created in the conversion process.

Use a Blob if you do not know the size that will be sent.

Edit:

Instead of using the TDataSet, use a TClientDataSet because, the facility to create the fields will be much greater:

var
  i    : Integer;
  JObj : TJSONObject;
begin
  if (aJSON <> EmptyStr) then
  begin
    JObj := TJSONObject.ParseJSONValue(aJSON) as TJSONObject;

    aDataset.Close;
    aDataset.FieldDefs.Clear; //Limpa os Campos Existentes

    for i := 0 to Pred(JObj.Size) do
    begin
      //Chave: JObj.Get(i).JsonString.Value
      if (Length(JObj.Get(i).JsonValue.Value) > 250) then
      begin
        aDataset.FieldDefs.Add(JObj.Get(i).JsonString.Value, ftBlob);
      end
      else
      begin
        aDataset.FieldDefs.Add(JObj.Get(i).JsonString.Value, ftString, 255);
      end;
    end;

    aDataset.CreateDataSet;

    for i := 0 to Pred(JObj.Size) do
    begin
      //Valor: JObj.Get(i).JsonValue.Value
      aDataset.Insert;
      aDataset.FieldByName(JObj.Get(i).JsonString.Value).AsString := JObj.Get(i).JsonValue.Value;
      aDataset.Post;
    end;

    JObj.Free;
  end;

This is an alternative so you don’t need to use the class TCustomJSONDataSetAdapter which has a pattern to follow, of course, it is possible to modify this class, but that is at the IDE level and not worth it as it would lose this progress in a next update!