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何惠民
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Add Issues document
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‎Issues.md

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# 在使用 Spring Boot 和 MyBatis 动态切换数据源时遇到的问题以及解决方法
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> 相关项目地址:[https://github.com/helloworlde/SpringBoot-DynamicDataSource](https://github.com/helloworlde/SpringBoot-DynamicDataSource)
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## 1. org.apache.ibatis.binding.BindingException: Invalid bound statement (not found)
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> 在使用了动态数据源后遇到了该问题,从错误信息来看是因为没有找到 `*.xml` 文件而导致的,但是在配置文件中
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确实添加了相关的配置,这种错误的原因是因为设置数据源后没有设置`SqlSessionFactoryBean`的 `typeAliasesPackage`
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和`mapperLocations`属性或属性无效导致的;
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- 解决方法:
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> 如果在应用的入口类中添加了 `@SpringBootApplication(exclude = DataSourceAutoConfiguration.class)`,
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在`DataSourceConfigure`类的中设置相关属性:
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```java
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@Bean
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@ConfigurationProperties(prefix = "mybatis")
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public SqlSessionFactoryBean sqlSessionFactoryBean() {
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SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
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sqlSessionFactoryBean.setDataSource(dynamicDataSource());
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return sqlSessionFactoryBean;
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}
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```
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或者直接配置(不推荐该方式):
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```java
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@Bean
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public SqlSessionFactoryBean sqlSessionFactoryBean() {
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SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
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sqlSessionFactoryBean.setTypeAliasesPackage("typeAliasesPackage");
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sqlSessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("mapperLocations"));
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sqlSessionFactoryBean.setDataSource(dynamicDataSource());
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return sqlSessionFactoryBean;
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}
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```
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## 2. Consider marking one of the beans as @Primary, updating the consumer to accept multiple beans, or using @Qualifier to identify the bean that should be consumed
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> 该异常在错误信息中已经说的很清楚了,是因为有多个 `DataSource` 的实例,所以无法确定该引用那个实例
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- 解决方法:
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> 为数据源的某个 `Bean` 添加 `@Primary` 注解,该 `Bean` 应当是通过 `DataSourceBuilder.create().build()`
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得到的 `Bean`,而不是通过 `new AbstractRoutingDataSource` 的子类实现的 `Bean`,在本项目中可以是 `master()`
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或 `slave()` 得到的 `DataSource`,不能是 `dynamicDataSource()` 得到的 `DataSource`
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## 3. 通过注解方式动态切换数据源无效
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- 请确认注解没有放到 DAO 层方法上, 因为会在 Service 层开启事务,所以当注解在 DAO 层时不会生效
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- 请确认以下 `Bean` 正确配置:
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```java
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@Bean("dynamicDataSource")
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public DataSource dynamicDataSource() {
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DynamicRoutingDataSource dynamicRoutingDataSource = new DynamicRoutingDataSource();
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Map<Object, Object> dataSourceMap = new HashMap<>(2);
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dataSourceMap.put("master", master());
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dataSourceMap.put("slave", slave());
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// Set master datasource as default
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dynamicRoutingDataSource.setDefaultTargetDataSource(master());
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// Set master and slave datasource as target datasource
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dynamicRoutingDataSource.setTargetDataSources(dataSourceMap);
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// To put datasource keys into DataSourceContextHolder to judge if the datasource is exist
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DynamicDataSourceContextHolder.dataSourceKeys.addAll(dataSourceMap.keySet());
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return dynamicRoutingDataSource;
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}
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@Bean
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@ConfigurationProperties(prefix = "mybatis")
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public SqlSessionFactoryBean sqlSessionFactoryBean() {
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SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
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// Here is very important, if don't config this, will can't switch datasource
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// put all datasource into SqlSessionFactoryBean, then will autoconfig SqlSessionFactory
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sqlSessionFactoryBean.setDataSource(dynamicDataSource());
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return sqlSessionFactoryBean;
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}
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```
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## 4. `@Transactional` 注解无效,发生异常不回滚
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- 请确认该 `Bean` 得到正确配置,并且`@Transactional` 的 `rollbackFor` 配置正确
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```java
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@Bean
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public PlatformTransactionManager transactionManager() {
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return new DataSourceTransactionManager(dynamicDataSource());
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}
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```
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## 5. 通过 AOP 判断 DAO 层方法名时切换数据源无效
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> 当切面指向了 DAO 层后无论如何设置切面的顺序,都无法在执行查询之前切换数据源,但是切面改为 Service 层后可以正常工作
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- 解决方法: 请确认 `@Transactional` 注解是加在方法上而不是 Service 类上,添加了 `@Transactional` 的方法因为在 Service 层开启了事务,
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会在事务结束之后才会切换数据源
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- 检出 `DataSourceTransactionManager` Bean 注入正确
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```java
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@Bean
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public PlatformTransactionManager transactionManager() {
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return new DataSourceTransactionManager(dynamicDataSource());
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}
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```
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## 6. The dependencies of some of the beans in the application context form a cycle
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- 错误信息:
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```
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The dependencies of some of the beans in the application context form a cycle:
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produceController (field private cn.com.hellowood.dynamicdatasource.service.ProductService cn.com.hellowood.dynamicdatasource.controller.ProduceController.productService)
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↓
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productService (field private cn.com.hellowood.dynamicdatasource.mapper.ProductDao cn.com.hellowood.dynamicdatasource.service.ProductService.productDao)
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↓
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productDao defined in file [/Users/hehuimin/Downloads/Dev/SpringBoot/DynamicDataSource/out/production/classes/cn/com/hellowood/dynamicdatasource/mapper/ProductDao.class]
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↓
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sqlSessionFactoryBean defined in class path resource [cn/com/hellowood/dynamicdatasource/configuration/DataSourceConfigurer.class]
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┌─────┐
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| dynamicDataSource defined in class path resource [cn/com/hellowood/dynamicdatasource/configuration/DataSourceConfigurer.class]
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↑ ↓
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| master defined in class path resource [cn/com/hellowood/dynamicdatasource/configuration/DataSourceConfigurer.class]
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↑ ↓
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| dataSourceInitializer
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└─────┘
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```
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> 这是因为在注入 `DataSource` 的实例的时候产生了循环调用,第一个注入的 Bean 依赖于其他的 Bean, 而被依赖的 Bean 产生依赖传递,依赖第一个
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注入的 Bean, 陷入了循环,无法启动项目
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- 解决方法:将 `@Primary` 注解指向没有依赖的 Bean,如:
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```java
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/**
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* master DataSource
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* @Primary 注解用于标识默认使用的 DataSource Bean,因为有三个 DataSource Bean,该注解可用于 master
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* 或 slave DataSource Bean, 但不能用于 dynamicDataSource Bean, 否则会产生循环调用
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*
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* @ConfigurationProperties 注解用于从 application.properties 文件中读取配置,为 Bean 设置属性
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* @return data source
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*/
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@Bean("master")
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@Primary
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@ConfigurationProperties(prefix = "application.server.db.master")
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public DataSource master() {
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return DataSourceBuilder.create().build();
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}
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@Bean("slave")
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@ConfigurationProperties(prefix = "application.server.db.slave")
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public DataSource slave() {
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return DataSourceBuilder.create().build();
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}
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@Bean("dynamicDataSource")
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public DataSource dynamicDataSource() {
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DynamicRoutingDataSource dynamicRoutingDataSource = new DynamicRoutingDataSource();
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Map<Object, Object> dataSourceMap = new HashMap<>(2);
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dataSourceMap.put("master", master());
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dataSourceMap.put("slave", slave());
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// Set master datasource as default
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dynamicRoutingDataSource.setDefaultTargetDataSource(master());
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// Set master and slave datasource as target datasource
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dynamicRoutingDataSource.setTargetDataSources(dataSourceMap);
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// To put datasource keys into DataSourceContextHolder to judge if the datasource is exist
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DynamicDataSourceContextHolder.dataSourceKeys.addAll(dataSourceMap.keySet());
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return dynamicRoutingDataSource;
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}
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```

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