Android Room 数据库事务 [英] Android Room database transactions

问题描述

使用 Android 中的新房间数据库，我有一个需要进行两个顺序操作的要求:

With the new Room Database in Android, I have a requirement where there are two sequential operations that needs to be made:

removeRows(ids);
insertRows(ids);

如果我运行它，我看到(在检查数据库时)缺少一些行 - 我假设它们在插入后被删除.即第一个操作与第二个操作并行运行.

If I run this, I see (on examining the db) that there are some rows missing - I assume they are being deleted after inserting. viz. the first operation is running in parallel to the second.

如果我使用事务块，例如这样，那么一切都很好 - 第一个操作似乎在执行第二个操作之前完成:

If I use a transaction block, such as this, then it's all fine - the first operation seems to complete before doing the second:

roomDb.beginTransaction();
removeRows(ids);
roomDb.endTransaction();

insertRows(ids);

如果我中间休息一下也没关系:

It's also fine if I give a sleep in-between instead:

removeRows(ids);
Thread.sleep(500);

insertRows(ids);

Room 的文档似乎并不多，我想知道当我要完成顺序操作时是否应该像上面那样使用事务块，或者有没有更好的方法.

There doesn't seem to be much documentation for Room, and was wondering if I should use the transaction block like the above when I have sequential operations to be done, or is there any better way of doing it.

EDIT:@CommonsWare 指出后，@Query 是异步的，而 @Insert 和 @Delete是同步的.鉴于此，我将如何获得将行删除为异步的查询:

EDIT: After @CommonsWare pointed out, @Query are asynchronous, while @Insert and @Delete are synchronous. In view of this, how would I get a query which deletes rows to be async:

@Query("DELETE from table WHERE id IN(:ids)")
int removeRows(List<Long> ids);

根据构建输出，如果我尝试将返回类型包装在 Flowable 中，我得到 删除方法必须返回 void 或返回 int(已删除的行数)代码>.

According to the build output I get Deletion methods must either return void or return int (the number of deleted rows), if I try to wrap the return type in a Flowable.

推荐答案

正如在 交易，您可以执行以下操作:

As pointed out on documentation for Transaction, you can do following:

 @Dao
 public abstract class ProductDao {
    @Insert
    public abstract void insert(Product product);

    @Delete
    public abstract void delete(Product product);

    @Transaction
    public void insertAndDeleteInTransaction(Product newProduct, Product oldProduct) {
         // Anything inside this method runs in a single transaction.
         insert(newProduct);
         delete(oldProduct);
     }
 }
 

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