[GitHub] [shardingsphere] pxzxj commented on issue #15629: Springboot with JPA, readwrite-splitting always on write-ds

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pxzxj commented on issue #15629:
URL: https://github.com/apache/shardingsphere/issues/15629#issuecomment-1105154441

   看了下上面都是国内的开发那就用中文吧，看起来方便点儿。
   
   这个问题的根源是Spring Data JPA默认所有方法都使用了事务，当然查询是只读事务，而ShardingSphere判断使用了事务就走主库，这两点可以参考Spring Data JPA的 [SimpleJpaRepository](https://github.com/spring-projects/spring-data-jpa/blob/a70fff4515d04be2e0f6f18edbcd7c1c0bff704e/spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/support/SimpleJpaRepository.java#L89) 类跟ShardingSphere的 [ReadwriteSplittingDataSourceRouter](https://github.com/apache/shardingsphere/blob/4354c3df905e38ca749e6ff40217037ffe2533df/shardingsphere-features/shardingsphere-readwrite-splitting/shardingsphere-readwrite-splitting-core/src/main/java/org/apache/shardingsphere/readwritesplitting/route/impl/ReadwriteSplittingDataSourceRouter.java#L56)
    类。
   比较理想的方法当然是ShardingSphere这边判断事务是不是只读的，不过这个不太确定ShardingSphere的开发团队愿不愿意改，就算改也要等到下个版本了。所以我这里提供两种调整Spring Data JPA事务的方案。
   ### 第一种：
   在Spring Boot的启动类加上 @EnableJpaRepositories(enableDefaultTransactions = false)，这样就关闭了Spring Data JPA的默认事务，但这也导致之前依赖默认事务的代码的出错，当然主要是涉及修改的操作，需要在Service或者Repository上手动添加@Transcational注解来解决报错。
   所以这种方法虽然配置简单，但对老代码有侵入性，要谨慎使用。
   ### 第二种：
   修改Spring Data JPA的事务判断，如果是只读事务(也就是readOnly=true)那就不开启事务，配置方法如下，其实就是创建 `IgnoreJPAReadOnlyTransactionBeanPostProcessor ` 类并声明为Bean
   
   ```java
   public class IgnoreJPAReadOnlyTransactionBeanPostProcessor implements BeanPostProcessor {
   
   	@Override
   	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
   		if (bean instanceof JpaRepositoryFactoryBean) {
   			RepositoryFactoryCustomizer customizer = new RepositoryFactoryCustomizer() {
   				@Override
   				public void customize(RepositoryFactorySupport repositoryFactory) {
   					repositoryFactory.addRepositoryProxyPostProcessor(new IgnoreJPAReadOnlyTransactionRepositoryProxyPostProcessor());
   				}
   			};
   			((RepositoryFactoryBeanSupport<?, ?, ?>) bean).addRepositoryFactoryCustomizer(customizer);
   		}
   		return bean;
   	}
   
   	private static class IgnoreJPAReadOnlyTransactionRepositoryProxyPostProcessor implements RepositoryProxyPostProcessor {
   
   		@Override
   		public void postProcess(ProxyFactory factory, RepositoryInformation repositoryInformation) {
   			Advisor[] advisors = factory.getAdvisors();
   			TransactionInterceptor transactionInterceptor = null;
   			for(Advisor advisor : advisors) {
   				if(advisor != null && advisor.getAdvice() instanceof TransactionInterceptor) {
   					transactionInterceptor = (TransactionInterceptor) advisor.getAdvice();
   					break;
   				}
   			}
   			if(transactionInterceptor != null) {
   				TransactionAttributeSource transactionAttributeSource = transactionInterceptor.getTransactionAttributeSource();
   				TransactionAttributeSource ignoreReadOnlyDelegate = (method, targetClass) -> {
   					TransactionAttribute transactionAttribute = transactionAttributeSource.getTransactionAttribute(method, targetClass);
   					if(transactionAttribute != null && transactionAttribute.isReadOnly()) {
   						return null;
   					}
   					return transactionAttribute;
   				};
   				transactionInterceptor.setTransactionAttributeSource(ignoreReadOnlyDelegate);
   			}
   		}
   	}
   }
   
   
   @Configuration
   public class WebConfig {
   	@Bean
   	public IgnoreJPAReadOnlyTransactionBeanPostProcessor ignoreJPAReadOnlyTransactionBeanPostProcessor() {
   		return new IgnoreJPAReadOnlyTransactionBeanPostProcessor();
   	}
   }
   ```
   这种方法经过测试原来代码也都能正常运行，只是禁用了只读事务，所以建议用这个方法。


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