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事务

创建和使用事务​

事务通过 DataSource 或 EntityManager 创建。 示例：

await myDataSource.transaction(async (transactionalEntityManager) => {
    // execute queries using transactionalEntityManager
})

或

await myDataSource.manager.transaction(async (transactionalEntityManager) => {
    // execute queries using transactionalEntityManager
})

所有需要在事务中执行的操作都必须在回调函数内完成：

await myDataSource.manager.transaction(async (transactionalEntityManager) => {
    await transactionalEntityManager.save(users)
    await transactionalEntityManager.save(photos)
    // ...
})

事务操作最重要的限制是必须始终使用提供的事务实体管理器实例—— 本例中的 transactionalEntityManager。禁止使用全局实体管理器。 所有操作必须使用提供的事务实体管理器执行。

指定隔离级别​

可通过在第一个参数位置指定隔离级别：

await myDataSource.manager.transaction(
    "SERIALIZABLE",
    (transactionalEntityManager) => {},
)

支持的隔离级别​

隔离级别的实现并非在所有数据库中都通用。每个驱动程序都会声明其支持的隔离级别，如果您请求了不支持的级别，TypeORM 将抛出错误。

CockroachDB

  • READ COMMITTED — requires the cluster setting sql.txn.read_committed_isolation.enabled, which is enabled by default in recent versions
  • REPEATABLE READ — requires the cluster setting sql.txn.repeatable_read_isolation.enabled, which is disabled by default (introduced in v24.3.0)
  • SERIALIZABLE (default)

CockroachDB maps weaker SQL isolation requests to stronger levels. The fallback behavior depends on the corresponding cluster settings. For example, when you request READ UNCOMMITTED, READ COMMITTED or REPEATABLE READ via SQL (e.g. BEGIN TRANSACTION ISOLATION LEVEL READ UNCOMMITTED), CockroachDB accepts the syntax and may run the transaction at a stricter level instead:

  • READ COMMITTED → runs as:
    • SERIALIZABLE if sql.txn.read_committed_isolation.enabled is false and sql.txn.repeatable_read_isolation.enabled is false
    • REPEATABLE READ if sql.txn.repeatable_read_isolation.enabled is true and sql.txn.read_committed_isolation.enabled is false
  • READ UNCOMMITTED → runs as:
    • SERIALIZABLE if sql.txn.read_committed_isolation.enabled is false and sql.txn.repeatable_read_isolation.enabled is false
    • READ COMMITTED if sql.txn.read_committed_isolation.enabled is true
    • REPEATABLE READ if sql.txn.repeatable_read_isolation.enabled is true and sql.txn.read_committed_isolation.enabled is false
  • REPEATABLE READ → runs as SERIALIZABLE if sql.txn.repeatable_read_isolation.enabled is false
Learn more

默认隔离级别​

您可以通过在 DataSource 配置中设置 isolationLevel 来为所有事务指定默认隔离级别：

const dataSource = new DataSource({
    type: "postgres",
    isolationLevel: "SERIALIZABLE",
    // ...
})

设置后，所有未显式指定隔离级别的事务都将使用此默认值。传递给 transaction() 或 startTransaction() 的显式隔离级别会覆盖此默认值。

使用 QueryRunner 创建并控制单数据库连接状态​

QueryRunner 提供单个数据库连接。 事务通过查询运行器进行管理。 单个事务只能在单个查询运行器上建立。 您可以手动创建查询运行器实例并控制事务状态。 示例：

// create a new query runner
const queryRunner = dataSource.createQueryRunner()

// establish real database connection using our new query runner
await queryRunner.connect()

// now we can execute any queries on a query runner, for example:
await queryRunner.query("SELECT * FROM users")

// we can also access entity manager that works with connection created by a query runner:
const users = await queryRunner.manager.find(User)

// lets now open a new transaction:
await queryRunner.startTransaction()

try {
    // execute some operations on this transaction:
    await queryRunner.manager.save(user1)
    await queryRunner.manager.save(user2)
    await queryRunner.manager.save(photos)

    // commit transaction now:
    await queryRunner.commitTransaction()
} catch (err) {
    // since we have errors let's rollback changes we made
    await queryRunner.rollbackTransaction()
} finally {
    // you need to release query runner which is manually created:
    await queryRunner.release()
}

QueryRunner 提供三种事务控制方法：

  • startTransaction - 在查询运行器实例内启动新事务

  • commitTransaction - 提交使用该查询运行器实例所做的所有更改

  • rollbackTransaction - 回滚使用该查询运行器实例所做的所有更改

详细了解查询运行器。