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...

        ZooFragmentViewModel viewModel = ViewModelProviders.of(this).get(ZooFragmentViewModel.class);
        viewModel.getZooUpdateResponse().observe(this, response -> {
            if (response != null) {
                switch (response.getStatus()) {
                    case Response.STATUS_LOADING:
                        showProgressBar(true);
                        break;
                    case Response.STATUS_SUCCESS:

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public class Response {

    public static final int STATUS_LOADING = 0, STATUS_SUCCESS = 1, STATUS_FAIL = 2;

    @Retention(SOURCE)
    @IntDef({STATUS_LOADING, STATUS_SUCCESS, STATUS_FAIL})
    @interface Status {
    }

    private final int mStatus;

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public class ZooDAO {

    private static Box<Zoo> getZooBox() {
        BoxStore boxStore = App.getBoxStore();
        return boxStore.boxFor(Zoo.class);
    }

    public static DataSubscription subscribeToZooList(DataObserver<List<Zoo>> observer) {
        return getZooBox().query().build().subscribe().on(AndroidScheduler.mainThread()).observer(observer);
    }

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public class ZooParser {

    private String mResponse;
    private Zoo mZoo;
    private List<Zoo> mZooList;
    private List<Animal> mAnimalList;
    private Gson mGson;

    public ZooParser(String response) {
        mResponse = response;

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public class ZooRepository {

    public static DataSubscription subscribeToZooList(DataObserver<List<Zoo>> observer) {
        return ZooDAO.subscribeToZooList(observer);
    }

    public static DataSubscription subscribeToZoo(DataObserver<Zoo> observer, long id, boolean singleUpdate) {
        return ZooDAO.subscribeToZoo(observer, id, singleUpdate);
    }

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public class ZooListViewModel extends BaseViewModel {

    private MutableLiveData<List<Zoo>> mZoosLiveData;

    public ZooListViewModel() {
        mZoosLiveData = new MutableLiveData<>();
        DataSubscription subscription = ZooRepository.subscribeToZooList(this::refreshZoos);
        addSubscription(subscription);
    }

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public abstract class BaseViewModel extends ViewModel {

    private final List<DataSubscription> mSubscriptions;

    @Override
    protected void onCleared() {
        super.onCleared();
        for (DataSubscription subscription : mSubscriptions) {
            if (!subscription.isCanceled()) {
                subscription.cancel();

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public class MainActivity extends AppCompatActivity {

    private ZooListViewModel mViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        RecyclerView recyclerView = findViewById(R.id.activity_main_recyclerview);

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@Entity
public class Animal {

    @Id
    private long id;

    private String name;
    private String image;
    private String group;

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@Entity
public class Zoo {

    @Id
    private long id;
    private String name;

    @Backlink
    public ToMany<Animal> animals;