Android Room数据库交易 [英] Android Room database transactions

问题描述

使用Android中新的Room数据库时，我需要在其中需要执行两个顺序的操作:

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);

如果运行此命令，我会发现(在检查数据库时)缺少某些行-我认为它们在插入后将被删除.即第一个操作与第二个操作并行进行.

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.

如果我使用这样的事务块，那就很好了-第一个操作似乎在完成第二个操作之前就完成了:

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);

如果我在两者之间进行睡眠，也可以:

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

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

insertRows(ids);

有关Room的文档似乎并不多，并且想知道当我要执行顺序操作时是否应该像上面那样使用事务块，或者是否有更好的方法来做到这一点.

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.

编辑:@CommonsWare指出后，@Query是异步的，而@Insert和@Delete是同步的.有鉴于此，我将如何获取一个删除行以使其异步的查询:

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，则会得到Deletion methods must either return void or return int (the number of deleted rows).

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

如

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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