问题描述

我正在尝试通过新的 android 房间库更新我的数据库，但它无法正常工作.这是我的方法

I am trying to update my database via new android room library, but it is not working. Here it is my approach

@IgnoreExtraProperties
@Entity(tableName = CarModel.TABLE_NAME,
    indices = {@Index(value = "car_name", unique = true)})
public class CarModel {

    public static final String TABLE_NAME = "cars";

    @PrimaryKey(autoGenerate = true)
    private int id;

    @ColumnInfo(name = "car_name")
    private String name;

    @ColumnInfo(name = "car_price")
    private String price;

    private String type;
    private String position;
}

MainActivity.java

MainActivity.java

viewModel.isCarsEmpty().observe(MainActivity.this, new Observer<Integer>() {
                    @Override
                    public void onChanged(@Nullable Integer rowCount) {
                        if (rowCount == 0) {
                            viewModel.insertItems(list);
                        } else {
                            viewModel.updateItems(list);
                        }
                    }
                });

CarViewModel.java

CarViewModel.java

public LiveData<Integer> isCarsEmpty() {
    return appDatabase.carDao().isDbEmpty();
}
    public void insertItems(List<CarModel> carModels) {
    new insertCarsAsyncTask(appDatabase).execute(carModels);
}

private class insertCarsAsyncTask extends AsyncTask<List<CarModel>, Void, Void> {
    private AppDatabase db;

    public insertCarsAsyncTask(AppDatabase appDatabase) {
        db = appDatabase;
    }

    @Override
    protected Void doInBackground(List<CarModel>... params) {
        db.carDao().insertCars(params[0]);
        return null;
    }
}

public void updateItems(List<CarModel> list) {
    new updateCarsTask(appDatabase).execute(list);
}

private class updateCarsTask extends AsyncTask<List<CarModel>, Void, Void> {
    private AppDatabase db;

    public updateCarsTask(AppDatabase appDatabase) {
        db = appDatabase;
    }

    @Override
    protected Void doInBackground(List<CarModel>... params) {
        db.carDao().updateCars(params[0]);
        return null;
    }
}

CarDao.java

CarDao.java

@Insert(onConflict = REPLACE)
void insertCars(List<CarModel> cars);

@Update
void updateCars(List<CarModel> param);

@Query("SELECT count(*) FROM " + CarModel.TABLE_NAME)
LiveData<Integer> isDbEmpty();

我做了调试，新数据来了，调用 viewModel.updateItems(list) 方法.提前致谢！

I did debugging, new data comes and calling viewModel.updateItems(list) method.Thanks in advance!

推荐答案

我很抱歉发布这个作为答案，但我还不允许添加简单的评论，所以这是我的想法:

I am sorry for posting this as an answer but I am not allowed to add a simple comment yet so here is my idea:

您是否尝试过仅使用 insertCars() 而不是 updateCars()?无论如何，您的 isCarsEmpty() LiveData 回调似乎一直被触发，因为当调用观察者时，数据库再次被更改.我不太确定您想要完成什么.

Have you tried using only insertCars() instead of updateCars()? Anyway it looks like your isCarsEmpty() LiveData callback gets triggered the whole time because when the observer is called the Database is altered again.. I am not quite sure what you want to accomplish tho.

这篇关于Android Room持久性库@Update不起作用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持跟版网！