Add Issues document

Author: 何惠民

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
+
+> 相关项目地址:[https://github.com/helloworlde/SpringBoot-DynamicDataSource](https://github.com/helloworlde/SpringBoot-DynamicDataSource)
+
+## 1. org.apache.ibatis.binding.BindingException: Invalid bound statement (not found)
+
+> 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
+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`
+和`mapperLocations`属性或属性无效导致的；
+
+- 解决方法：
+
+> 如果在应用的入口类中添加了 `@SpringBootApplication(exclude = DataSourceAutoConfiguration.class)`,
+在`DataSourceConfigure`类的中设置相关属性：
+
+```java
+    @Bean
+    @ConfigurationProperties(prefix = "mybatis")
+    public SqlSessionFactoryBean sqlSessionFactoryBean() {
+        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
+        sqlSessionFactoryBean.setDataSource(dynamicDataSource());
+        return sqlSessionFactoryBean;
+    }
+```
+
+或者直接配置(不推荐该方式)：
+
+```java
+    @Bean
+    public SqlSessionFactoryBean sqlSessionFactoryBean() {
+        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
+        sqlSessionFactoryBean.setTypeAliasesPackage("typeAliasesPackage");
+        sqlSessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("mapperLocations"));
+        sqlSessionFactoryBean.setDataSource(dynamicDataSource());
+        return sqlSessionFactoryBean;
+    }
+```
+
+
+
+
+
+## 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
+
+> 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
+
+- 解决方法：
+
+> 为数据源的某个 `Bean` 添加 `@Primary` 注解，该 `Bean` 应当是通过 `DataSourceBuilder.create().build()`
+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()`
+或 `slave()` 得到的 `DataSource`，不能是 `dynamicDataSource()` 得到的 `DataSource`
+
+## 3. 通过注解方式动态切换数据源无效
+
+- 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
+- 请确认以下 `Bean` 正确配置：
+
+```java
+    @Bean("dynamicDataSource")
+    public DataSource dynamicDataSource() {
+        DynamicRoutingDataSource dynamicRoutingDataSource = new DynamicRoutingDataSource();
+        Map<Object, Object> dataSourceMap = new HashMap<>(2);
+        dataSourceMap.put("master", master());
+        dataSourceMap.put("slave", slave());
+
+        // Set master datasource as default
+        dynamicRoutingDataSource.setDefaultTargetDataSource(master());
+        // Set master and slave datasource as target datasource
+        dynamicRoutingDataSource.setTargetDataSources(dataSourceMap);
+
+        // To put datasource keys into DataSourceContextHolder to judge if the datasource is exist
+        DynamicDataSourceContextHolder.dataSourceKeys.addAll(dataSourceMap.keySet());
+        return dynamicRoutingDataSource;
+    }
+
+    @Bean
+    @ConfigurationProperties(prefix = "mybatis")
+    public SqlSessionFactoryBean sqlSessionFactoryBean() {
+        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
+        // Here is very important, if don't config this, will can't switch datasource
+        // put all datasource into SqlSessionFactoryBean, then will autoconfig SqlSessionFactory
+        sqlSessionFactoryBean.setDataSource(dynamicDataSource());
+        return sqlSessionFactoryBean;
+    }
+
+```
+
+## 4. `@Transactional` 注解无效，发生异常不回滚
+
+- 请确认该 `Bean` 得到正确配置，并且`@Transactional` 的 `rollbackFor` 配置正确
+
+```java
+    @Bean
+    public PlatformTransactionManager transactionManager() {
+        return new DataSourceTransactionManager(dynamicDataSource());
+    }
+    
+```
+
+## 5. 通过 AOP 判断 DAO 层方法名时切换数据源无效
+
+> 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
+
+- 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，
+会在事务结束之后才会切换数据源
+
+- 检出 `DataSourceTransactionManager` Bean 注入正确
+
+```java
+    @Bean 
+    public PlatformTransactionManager transactionManager() {
+        return new DataSourceTransactionManager(dynamicDataSource());
+    }
+```
+
+## 6. The dependencies of some of the beans in the application context form a cycle
+
+- 错误信息：
+
+```
+The dependencies of some of the beans in the application context form a cycle:
+
+   produceController (field private cn.com.hellowood.dynamicdatasource.service.ProductService cn.com.hellowood.dynamicdatasource.controller.ProduceController.productService)
+      ↓
+   productService (field private cn.com.hellowood.dynamicdatasource.mapper.ProductDao cn.com.hellowood.dynamicdatasource.service.ProductService.productDao)
+      ↓
+   productDao defined in file [/Users/hehuimin/Downloads/Dev/SpringBoot/DynamicDataSource/out/production/classes/cn/com/hellowood/dynamicdatasource/mapper/ProductDao.class]
+      ↓
+   sqlSessionFactoryBean defined in class path resource [cn/com/hellowood/dynamicdatasource/configuration/DataSourceConfigurer.class]
+┌─────┐
+|  dynamicDataSource defined in class path resource [cn/com/hellowood/dynamicdatasource/configuration/DataSourceConfigurer.class]
+↑     ↓
+|  master defined in class path resource [cn/com/hellowood/dynamicdatasource/configuration/DataSourceConfigurer.class]
+↑     ↓
+|  dataSourceInitializer
+└─────┘
+```
+
+> 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
+注入的 Bean, 陷入了循环，无法启动项目
+
+- 解决方法：将 `@Primary` 注解指向没有依赖的 Bean，如：
+```java
+
+    /**
+     * master DataSource
+     * @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
+     * 或 slave DataSource Bean, 但不能用于 dynamicDataSource Bean, 否则会产生循环调用 
+     * 
+     * @ConfigurationProperties 注解用于从 application.properties 文件中读取配置，为 Bean 设置属性 
+     * @return data source
+     */
+    @Bean("master")
+    @Primary
+    @ConfigurationProperties(prefix = "application.server.db.master")
+    public DataSource master() {
+        return DataSourceBuilder.create().build();
+    }
+
+    @Bean("slave")
+    @ConfigurationProperties(prefix = "application.server.db.slave")
+    public DataSource slave() {
+        return DataSourceBuilder.create().build();
+    }
+
+    @Bean("dynamicDataSource")
+    public DataSource dynamicDataSource() {
+        DynamicRoutingDataSource dynamicRoutingDataSource = new DynamicRoutingDataSource();
+        Map<Object, Object> dataSourceMap = new HashMap<>(2);
+        dataSourceMap.put("master", master());
+        dataSourceMap.put("slave", slave());
+
+        // Set master datasource as default
+        dynamicRoutingDataSource.setDefaultTargetDataSource(master());
+        // Set master and slave datasource as target datasource
+        dynamicRoutingDataSource.setTargetDataSources(dataSourceMap);
+
+        // To put datasource keys into DataSourceContextHolder to judge if the datasource is exist
+        DynamicDataSourceContextHolder.dataSourceKeys.addAll(dataSourceMap.keySet());
+        return dynamicRoutingDataSource;
+    }
+```