Room DataData存在于表中，但查询返回null

Question

我正在尝试使用Room persistence db构建一个应用程序，我想获取存储在Business表中的数据并开始使用它。 这是我的DAO

@Dao
public interface BusinessDao {

    @Query("SELECT * FROM Business")
    Business getAll();

    @Query("SELECT business_name, business_phone, business_address, business_manager FROM Business")
    public List<BusinessModel> getTuple();

    @Query("UPDATE Business SET business_name = :businessName, business_address = :businessAddress, business_phone = :businessPhone, business_manager = :businessManager WHERE bid = :bid")
    void updateBusinessById(String businessName, String businessAddress, String businessPhone, String businessManager, int bid);

    @Insert
    void insertAll(Business... businesses);

    @Delete
    void delete(Business business);
}

更新，插入和删除均可，但是getAll和getTuple始终返回null。 这是我的实体

@Entity(tableName = "Business")
public class Business extends BaseObservable implements Serializable {

    @PrimaryKey(autoGenerate = true)
    private int bid;

    @ColumnInfo(name = "business_name")
    private String businessName;

    @ColumnInfo(name = "business_address")
    private String businessAddress;

    @ColumnInfo(name = "business_phone")
    private String businessPhone;

    @ColumnInfo(name = "business_manager")
    private String businessManager;

    @Ignore
    private boolean displayError;

    public int getBid() {
        return bid;
    }

    public void setBid(int bid) {
        this.bid = bid;
    }

    @Bindable
    public boolean isDisplayError() {
        return displayError;
    }

    public void setDisplayError(boolean displayError) {
        this.displayError = displayError;
        notifyPropertyChanged(BR.displayError);
    }


    @Bindable
    public String getBusinessName() {
        if (businessName == null)
            return "";
        return businessName;
    }

    @NonNull
    public String getBusinessName1() {
        if (businessName == null)
            return "";
        return businessName;
    }

    @Bindable({"displayError", "businessName"})
    public String getBusinessNameError() {
        if (!isDisplayError()) {
            return "";
        }
        if (getBusinessName().isEmpty()) {
            return "BUSINESS NAME IS EMPTY!";
        }
        return "";
    }

    public void setBusinessName(String businessName) {
        this.businessName = businessName;
        notifyPropertyChanged(BR.businessName);
    }

.
.
.
}

我已经创建了一个模型来访问getTuple并返回数据，这就是模型

public class BusinessModel implements Serializable {

        @ColumnInfo(name="business_name")
        public String businessName;

        @ColumnInfo(name="business_address")
        public String businessAddress;

        @ColumnInfo(name="business_phone")
        public String businessPhone;

        @ColumnInfo(name="business_manager")
        public String businessManager;

    public String getBusinessName() {
        if (businessName == null)
            return "";
        return businessName;
    }

    public void setBusinessName(String businessName) {
        this.businessName = businessName;
    }
.
.
.

还有我的DatabaseAsyncUtil

public class GetBusinessModelAsyncTask extends AsyncTask<Void, Void,
        List<BusinessModel>> {

    private AppDatabase db;
    private final DataBaseCallBack dataBaseCallBack;

    public GetBusinessModelAsyncTask(AppDatabase userDatabase, DataBaseCallBack dataBaseCallBack) {
        db = userDatabase;
        this.dataBaseCallBack = dataBaseCallBack;
    }

    @Override
    protected List<BusinessModel> doInBackground(Void... voids) {
        List<BusinessModel> businessModel = db.businessDao().getTuple();
        return businessModel;
    }

    @Override
    protected void onPostExecute(List<BusinessModel> businessModelList) {
        super.onPostExecute(businessModelList);
        if (businessModelList != null) {
            dataBaseCallBack.onSuccess(businessModelList, ApplicationConstants.SUCCESS_MSG);
        } else
            dataBaseCallBack.onFailure(ApplicationConstants.ERROR_CODE, ApplicationConstants.ERROR_MSG);
    }

}

//kkk
class GetBusinessAsyncTask extends AsyncTask<Void, Void,
        Business> {

    private final DataBaseCallBack dataBaseCallBack;
    private AppDatabase db;

    GetBusinessAsyncTask(AppDatabase userDatabase, DataBaseCallBack dataBaseCallBack) {
        db = userDatabase;
        this.dataBaseCallBack = dataBaseCallBack;
    }

    @Override
    protected Business doInBackground(Void... voids) {
        Business business;
        try {
            business = db.businessDao().getAll();
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
        return business;
    }

    @Override
    protected void onPostExecute(Business business) {
        super.onPostExecute(business);
        if (business != null)
            dataBaseCallBack.onSuccess(business, ApplicationConstants.SUCCESS_MSG_2_SIGN_IN);
        else
            dataBaseCallBack.onFailure(ApplicationConstants.ERROR_CODE, ApplicationConstants.ERROR_MSG_2);
    }
}

我对Room db并不是很熟悉。我正在尝试通过在应用上实施来学习，而我一直被困在这里。