Mybatis plus的多数据源@DS切换为什么不起作用了，谁的锅，@Transactional |
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Mybatis plus的多数据源@DS切换为什么不起作用了，谁的锅，@Transactional
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由于使用了微服务，会有多个数据库的情况，有时业务需要，需要切换数据源，所以使用了Mybatis plus的@DS来切换多数据源 yml数据库配置如下： spring: datasource: dynamic: primary: master datasource: master: driverClassName: com.mysql.cj.jdbc.Driver url: jdbc:mysql://user username: root password: root common: driverClassName: com.mysql.cj.jdbc.Driver url: jdbc:mysql://book username: root password: rootservice如下，默认是master数据源 @Service @Slf4j public class MasterService { @Autowired UserService userService; @Autowired BookService bookService; /**必须master库方法先执行，才能回滚，达到事务效果*/ @Transactional(rollbackFor = Exception.class) public void upload(ReqDto reqDto){ userService.save(reqDto); bookService.save(reqDto); } }userService @Service @Log4j2 public class UserService extends ServiceImpl { @Resource private UserMapper userMapper; public void save(ReqDto reqDto) { userMapper.save(reqDto); } }bookService @Service @Log4j2 @DS("common") public class BookService extends ServiceImpl { @Resource private BookMapper bookMapper; public void save(ReqDto reqDto) { bookMapper.save(reqDto); } }但是神奇的事发生的，bookService的数据库应该是common，但是却是master的，也就是说@DS切换数据源没有起作用 于是开始排查 去除MasterService.upload上面的@Transactional，数据源切换正常，但是事务无效BookService的save上面加@Transactional，数据源没有切换BookService的save上面加@Transactional(propagation = Propagation.REQUIRES_NEW)，数据源切换，且事务有效原因： 开启事务的同时，会从数据库连接池获取数据库连接；如果内层的service使用@DS切换数据源，只是又做了一层拦截，但是并没有改变整个事务的连接;在这个事务内的所有数据库操作，都是在事务连接建立之后，所以会产生数据源没有切换的问题;为了使@DS起作用，必须替换数据库连接，也就是改变事务的传播机智，产生新的事务，获取新的数据库连接;所以bookService的save方法上除了加@Transactional外，还需要设置propagation = Propagation.REQUIRES_NEW 使得代码走以下逻辑： private TransactionStatus handleExistingTransaction( .....省略..... if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW) { if (debugEnabled) { logger.debug("Suspending current transaction, creating new transaction with name [" + definition.getName() + "]"); } SuspendedResourcesHolder suspendedResources = suspend(transaction); try { return startTransaction(definition, transaction, debugEnabled, suspendedResources); } catch (RuntimeException | Error beginEx) { resumeAfterBeginException(transaction, suspendedResources, beginEx); throw beginEx; } } .....省略.....)在走startTransaction，再走doBegin，重新创建新事务，获取新的数据库连接，从而得到@DS的数据源 startTransaction(definition, transaction, debugEnabled, suspendedResources); protected void doBegin(Object transaction, TransactionDefinition definition) { DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction; Connection con = null; try { if (!txObject.hasConnectionHolder() || txObject.getConnectionHolder().isSynchronizedWithTransaction()) { Connection newCon = obtainDataSource().getConnection();//获取数据库连接 if (logger.isDebugEnabled()) { logger.debug("Acquired Connection [" + newCon + "] for JDBC transaction"); } txObject.setConnectionHolder(new ConnectionHolder(newCon), true); } txObject.getConnectionHolder().setSynchronizedWithTransaction(true); con = txObject.getConnectionHolder().getConnection(); Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition); txObject.setPreviousIsolationLevel(previousIsolationLevel); txObject.setReadOnly(definition.isReadOnly()); // Switch to manual commit if necessary. This is very expensive in some JDBC drivers, // so we don't want to do it unnecessarily (for example if we've explicitly // configured the connection pool to set it already). if (con.getAutoCommit()) { txObject.setMustRestoreAutoCommit(true); if (logger.isDebugEnabled()) { logger.debug("Switching JDBC Connection [" + con + "] to manual commit"); } con.setAutoCommit(false); } .....省略.....)最终代码如下，只需要修改的是bookService bookService @Service @Log4j2 @DS("common") public class BookService extends ServiceImpl { @Resource private BookMapper bookMapper; @Transactional(propagation = Propagation.REQUIRES_NEW) public void save(ReqDto reqDto) { bookMapper.save(reqDto); } } @DS数据源切换生效@Transaction事务生效需要注意： master：userService common：bookService common数据库的操作，需要在master之后，这样当bookService.save失败，会使得userService回滚； 如果common的操作先，那当userService失败，无法使bookService回滚 会回滚 @Transactional(rollbackFor = Exception.class) public void upload(ReqDto respDto){ userService.save(respDto); bookService.save(respDto); }不会回滚 @Transactional(rollbackFor = Exception.class) public void upload(ReqDto respDto){ bookService.save(respDto); userService.save(respDto); } |
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