房间交易回滚

Question

根据room documentation事务回滚事务中的每个查询以防出错。

所以我在这里测试了回滚：

@Transaction
public Completable updateTable1(Table table1) {
    return Completable.fromAction(
            () -> 
                table1.setNotice("why am i updateed????");
                synchronousUpdate(table1);
                table1.setForeignKeyId(90); //some random foreign key which does not exsist so it throws an exception
                synchronousUpdate(table1);
            }
    );
}

@Update
void synchronousUpdate(T obj);

即使第二次更新引发错误，我的 table1 仍然会更新。

原因可能是什么？我是因为我返回一个可完成的而不是像 void 这样的同步返回值？

Answer 1

文件说

除非在方法体中抛出异常，否则事务将被标记为成功。

实际上并没有说异常将被管理，尽管 ROLLBACK 将跳过，即 setTransactionSuccessful 被跳过并执行 endTransaction。如果您查看生成的代码，例如编码方法是：-

@Transaction
public boolean update4(Bookmark b1, Bookmark b2) {
    if (update(b1) > 0) {
        if (update(b2) < 1) {
            abort(b1);
            return false;
        }
    } else {
            abort(b1);
        return false;
    }
    return true;
}

Room生成的代码是：-

  @Override
  public boolean update4(final Bookmark b1, final Bookmark b2) {
    __db.beginTransaction();
    try {
      boolean _result = AllDao_Impl.super.update4(b1, b2);
      __db.setTransactionSuccessful();
      return _result;
    } finally {
      __db.endTransaction();
    }
  }

没有catch，所以你需要相应地处理异常。

考虑以下（给出的先前答案的修改版本）：-

    b1.setPostUrl("YetAnotherURL");
    b5.setPostTitle("P5");
    b5.setPostUrl("U5");
    try {
        dao.update4(b1, b5);
    }
    catch (Exception e) {
        e.printStackTrace();
    }
    logInfo("-D1");
    dao.update4(b1,b5);
    logInfo("-D2");

基本上相同的更新，由于 id 不存在而不会更新（返回 0），运行两次。不同之处在于第一个是在 try/catch 块中。

日志结果：-

2021-07-09 12:04:38.344 W/System.err: android.database.sqlite.SQLiteConstraintException: UNIQUE constraint failed: mylist_data.ID (code 1555 SQLITE_CONSTRAINT_PRIMARYKEY)
2021-07-09 12:04:38.348 W/System.err:     at android.database.sqlite.SQLiteConnection.nativeExecuteForLastInsertedRowId(Native Method)
2021-07-09 12:04:38.349 W/System.err:     at android.database.sqlite.SQLiteConnection.executeForLastInsertedRowId(SQLiteConnection.java:796)
2021-07-09 12:04:38.349 W/System.err:     at android.database.sqlite.SQLiteSession.executeForLastInsertedRowId(SQLiteSession.java:788)
2021-07-09 12:04:38.349 W/System.err:     at android.database.sqlite.SQLiteStatement.executeInsert(SQLiteStatement.java:86)
2021-07-09 12:04:38.349 W/System.err:     at androidx.sqlite.db.framework.FrameworkSQLiteStatement.executeInsert(FrameworkSQLiteStatement.java:51)
2021-07-09 12:04:38.349 W/System.err:     at androidx.room.EntityInsertionAdapter.insertAndReturnId(EntityInsertionAdapter.java:114)
2021-07-09 12:04:38.349 W/System.err:     at a.a.so67958704javaroomconvertexistingdb.AllDao_Impl.abort(AllDao_Impl.java:133)
2021-07-09 12:04:38.349 W/System.err:     at a.a.so67958704javaroomconvertexistingdb.AllDao.update4(AllDao.java:40)
2021-07-09 12:04:38.350 W/System.err:     at a.a.so67958704javaroomconvertexistingdb.AllDao_Impl.access$001(AllDao_Impl.java:22)
2021-07-09 12:04:38.350 W/System.err:     at a.a.so67958704javaroomconvertexistingdb.AllDao_Impl.update4(AllDao_Impl.java:159)
2021-07-09 12:04:38.350 W/System.err:     at a.a.so67958704javaroomconvertexistingdb.MainActivity.onCreate(MainActivity.java:78)
....
2021-07-09 12:04:38.353 D/BMINFO-D1: ID = 1 PostTitle = P1 PostURL =AnotherURL
2021-07-09 12:04:38.353 D/BMINFO-D1: ID = 2 PostTitle = P2 PostURL =U2
2021-07-09 12:04:38.353 D/BMINFO-D1: ID = 3 PostTitle = P3 PostURL =U3
2021-07-09 12:04:38.353 D/BMINFO-D1: ID = 4 PostTitle = P4 PostURL =U4
2021-07-09 12:04:38.355 D/AndroidRuntime: Shutting down VM
2021-07-09 12:04:38.358 E/AndroidRuntime: FATAL EXCEPTION: main
    Process: a.a.so67958704javaroomconvertexistingdb, PID: 14230
    java.lang.RuntimeException: Unable to start activity ComponentInfo{a.a.so67958704javaroomconvertexistingdb/a.a.so67958704javaroomconvertexistingdb.MainActivity}: android.database.sqlite.SQLiteConstraintException: UNIQUE constraint failed: mylist_data.ID (code 1555 SQLITE_CONSTRAINT_PRIMARYKEY)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)

注意第一个异常被捕获并打印出来，不是致命异常，第二个是。