Objectbox-java: Gson doesn't parse from 'JSON to entity' which contains a ToOne relation object.

[sandeep466github]

My Entity is as follows.

@Entity
public class Conference {

@Id(assignable = true)
public long conferenceID;
public ToOne<ConferenceAgenda> agenda;

}

I am getting a JSON response from server as

{"conferenceID":2,"agenda":{"days":[{"title":"day-1"}]}}

I am trying to parse the above JSON to the entity. "conferenceID" is getting parsed but the "agenda"
doesn't get parsed. Am I doing something wrong or is there any other way I can parse the JSON.

objectboxVersion : 1.1.0

[rohitgupta1694]

@sandeep466github Please refer to #104 for better understanding.

[greenrobot]

@sandeep466github Is there a way to tell GSON to use a setter instead of using the field directly? Then you could have a setAgenda(ConferenceAgenda confAgenda) setter calling agenda.setTarget(confAgenda).

[rohitgupta1694]

@greenrobot What i have observed and encountered while parsing json response through GSON is when we provide a ToOne or ToMany types to the GSON then it always throw StackOverFlow error.

[greenrobot]

@errohitgupta Can you share the relevant part of the stack in a new issue if you think this is a bug? Thank you!

[sandeep466github]

@greenrobot we are using Gson with direct access of members instead of setters and getters. Can you elaborate some more on what you said.

[greenrobot]

OH GSON seems to still force you to use fields: https://github.com/google/gson/issues/232

[greenrobot]

I was never a big Gson fan (favoring Moshi and Jackson personally) and haven't done much with it. Maybe there are configurations to allow this, but I don't know.

Another possibility could be to provide some custom serializer/deserializer for ToOne, see https://github.com/google/gson/blob/master/UserGuide.md#TOC-Custom-Serialization-and-Deserialization

[sandeep466github]

@greenrobot So do you recommend JACKSON instead of GSON to go hand to hand with Objectbox. If yes then I will switch to JACKSON. I will also take a look into serializer/deserializer.

[greenrobot-team]

Maybe a possible workaround: add a field annotated with @Transient (the ObjectBox version, which should be ignored by Gson) that Gson can deserialize into. Then post-process your objects and manually call agenda.setTarget(parsedAgenda).

Edit: but I suppose only writing a custom de/serializer for each entity works properly. That's a lot of work though. But it can properly set the ToOne/ToMany values:

entity.order.setTarget(order);
entity.orders.addAll(orders);

-ut

[crazyxu]

@greenrobot-team so how to Initialization the agenda in kotlin :lateinit var agenda: ToOne<>

[eftokay83]

Is here already a (easy) solution known?

[greenrobot-team]

Had to work with Gson recently. You probably have to write a custom deserializer for each entity. An example:

@Entity class User {
    private ToOne<Status> status;
    private ToMany<Address> addresses;
    // TODO getters/setters
}

class UserDeserializer implements JsonDeserializer<User> {
    @Override
    public User deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
            throws JsonParseException {
        JsonObject userJson = json.getAsJsonObject();
        User user = new User(); // ToOne and ToMany initialized here through code injected by ObjectBox plugin

        // ToOne
        JsonObject statusJson = userJson.getAsJsonObject("status");
        Status status = context.deserialize(statusJson, Status.class);
        user.getStatus().setTarget(status);

        // ToMany
        JsonArray addressesJson = userJson.getAsJsonArray("addresses");
        Type addressListType = new TypeToken<ArrayList<Address>>(){}.getType();
        ArrayList<Address> addresses = context.deserialize(addressesJson, addressListType);
        user.getAddresses().addAll(addresses);

        // TODO parse other properties

        return user;
    }
}

Also posted this in https://github.com/objectbox/objectbox-java/issues/104#issuecomment-496384138.

-Uwe

[greenrobot-team]

Closing this in favor of #104. Please thumbs up that one.