背景： mybatis-plus + 多数据源启动项目一直报错：

2024-02-22 14:31:20,298-WARN-[AbstractApplicationContext.java:591]-[main]-Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'accountController': Unsatisfied dependency expressed through field 'userService'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userService': Unsatisfied dependency expressed through field 'baseMapper'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'IUserDAO' defined in file [D:\Epson\vipwp-springboot2\target\classes\com\epson\vipwp\dao\IUserDAO.class]: Unsatisfied dependency expressed through bean property 'sqlSessionTemplate'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'org.mybatis.spring.SqlSessionTemplate' available: expected single matching bean but found 4: sqlSessionTemplate,sqlSessionTemplatePop,sqlSessionTemplateOqc,sqlSessionTemplateQpost
2024-02-22 14:31:20,303-INFO-[DirectJDKLog.java:173]-[main]-Stopping service [Tomcat]
2024-02-22 14:31:20,351-ERROR-[LoggingFailureAnalysisReporter.java:40]-[main]-

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APPLICATION FAILED TO START
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Description:

file [D:\Epson\vipwp-springboot2\target\classes\com\epson\vipwp\dao\IUserDAO.class] required a single bean, but 4 were found:
    - sqlSessionTemplate: defined by method 'sqlSessionTemplateAssy' in class path resource [com/epson/vipwp/core/DataSourceConfig.class]
    - sqlSessionTemplatePop: defined by method 'sqlSessionTemplatePop' in class path resource [com/epson/vipwp/core/DataSourceConfig.class]
    - sqlSessionTemplateOqc: defined by method 'sqlSessionTemplateOqc' in class path resource [com/epson/vipwp/core/DataSourceConfig.class]
    - sqlSessionTemplateQpost: defined by method 'sqlSessionTemplateQpost' in class path resource [com/epson/vipwp/core/DataSourceConfig.class]

Action:

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

也就是找到4个 sqlSessionTemplate因此mybatis plus不知道该使用哪个数据源，

网上各种找解决办法都是说在

@Bean(name = "sqlSessionFactory")的定义上面添加@Primary标签，当不在service上面使用@DS注解时就使用@Primary标签定义的默认的数据源，但是无效，后来尝试了在

@Bean(name = "sqlSessionTemplate")的上面添加@Primary注解，居然神奇的解决了

以下是完整的4个数据源配置：

package com.xxx;

import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.SqlSessionFactoryBean;
import org.mybatis.spring.SqlSessionTemplate;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.jdbc.DataSourceBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.jdbc.core.JdbcTemplate;

import javax.sql.DataSource;
import java.util.Objects;

/**
 * 数据源配置类
 */
@Configuration
public class DataSourceConfig {
//以下四个DataSource不能定义在这，否则将循环引用，springboot无法启动
//  @Autowired  private DataSource dataSourceAssy; // 装配ASSY数据源  ---//省略后面几个，反正也不能定义
//貌似后面3个SqlSessionFactory根本没有被用到，因此注释掉

    // 定义ASSY数据源相关的Bean
    // 使用@Primary注解表示当存在多个同类型的Bean时，优先选择该Bean
    @Primary
    @Bean(name = "dataSourceAssy")
    @ConfigurationProperties(prefix = "spring.datasource.assy")
    public DataSource dataSourceAssy() {
        return DataSourceBuilder.create().build();
    } // 使用DataSourceBuilder创建数据源
    @Primary // 指定为默认jdbcTemplateAssy
    @Bean(name = "jdbcTemplateAssy")
    public JdbcTemplate jdbcTemplateAssy(@Qualifier("dataSourceAssy") DataSource dataSource) {
        return new JdbcTemplate(dataSource); // 创建JdbcTemplate实例，用于执行SQL操作
    }
    @Primary // 指定为默认SqlSessionFactory
    @Bean(name = "sqlSessionFactory") //默认数据源不能乱起名字，必须叫sqlSessionFactory
    public SqlSessionFactory sqlSessionFactoryAssy(@Qualifier("dataSourceAssy") DataSource dataSource) throws Exception {
        SqlSessionFactoryBean factory = new SqlSessionFactoryBean();// 创建SqlSessionFactoryBean实例
        factory.setDataSource(dataSource);// 设置数据源
        // 加载mybatis的相关配置文件，如果有的话
        // factoryBean.setConfigLocation(new ClassPathResource("mybatis-config.xml"));
        // 设置实体类别名包扫描
        factory.setTypeAliasesPackage("com.epson.vipwp.domain");
        // 添加 SqlSessionTemplate Bean 的定义
        SqlSessionTemplate sqlSessionTemplate = new SqlSessionTemplate(Objects.requireNonNull(factory.getObject()));
        return factory.getObject();// 返回SqlSessionFactory实例，用于创建SqlSession，使用SqlSession调用sql时不需要指定数据源，因为就在此处指定了
    }
    //如果要将 SqlSessionTemplate 作为单独的 Bean 注入，可以这样：
     @Primary
     @Bean(name = "sqlSessionTemplate")
     public SqlSessionTemplate sqlSessionTemplateAssy(SqlSessionFactory sqlSessionFactoryAssy) {
         return new SqlSessionTemplate(sqlSessionFactoryAssy);
     }

    //POP
    @Bean(name = "dataSourcePop")
    @ConfigurationProperties(prefix = "spring.datasource.pop")
    public DataSource dataSourcePop() {
        return DataSourceBuilder.create().build();
    }// 使用DataSourceBuilder创建POP数据源
    @Bean(name = "jdbcTemplatePop")
    public JdbcTemplate jdbcTemplatePop(@Qualifier("dataSourcePop") DataSource dataSource) {
        return new JdbcTemplate(dataSource);// 创建POP JdbcTemplate实例，用于执行SQL操作
    }

    @Bean(name = "sqlSessionFactoryPop")
    public SqlSessionFactory sqlSessionFactoryPop(@Qualifier("dataSourcePop") DataSource dataSource) throws Exception {
        SqlSessionFactoryBean factory = new SqlSessionFactoryBean();// 创建SqlSessionFactoryBean实例
        factory.setDataSource(dataSource);// 设置数据源
        factory.setTypeAliasesPackage("com.epson.vipwp.domain");
        // 添加 SqlSessionTemplate Bean 的定义
        SqlSessionTemplate sqlSessionTemplate = new SqlSessionTemplate(Objects.requireNonNull(factory.getObject()));
        return factory.getObject();// 返回SqlSessionFactory实例，用于创建SqlSession，使用SqlSession调用sql时不需要指定数据源，因为就在此处指定了
    }
    //如果要将 SqlSessionTemplate 作为单独的 Bean 注入，可以这样：
    @Bean(name = "sqlSessionTemplatePop")
    public SqlSessionTemplate sqlSessionTemplatePop(SqlSessionFactory sqlSessionFactoryPop) {
        return new SqlSessionTemplate(sqlSessionFactoryPop);
    }

    //OQC
    @Bean(name = "dataSourceOqc")
    @ConfigurationProperties(prefix = "spring.datasource.oqc")
    public DataSource dataSourceOqc() {
        return DataSourceBuilder.create().build();
    }
    @Bean(name = "jdbcTemplateOqc")
    public JdbcTemplate jdbcTemplateOqc(@Qualifier("dataSourceOqc") DataSource dataSource) {
        return new JdbcTemplate(dataSource);
    }

    @Bean(name = "sqlSessionFactoryOqc")
    public SqlSessionFactory sqlSessionFactoryOqc(@Qualifier("dataSourceOqc") DataSource dataSource) throws Exception {
        SqlSessionFactoryBean factory = new SqlSessionFactoryBean();// 创建SqlSessionFactoryBean实例
        factory.setDataSource(dataSource);// 设置数据源
        factory.setTypeAliasesPackage("com.epson.vipwp.domain");
        // 添加 SqlSessionTemplate Bean 的定义
        SqlSessionTemplate sqlSessionTemplate = new SqlSessionTemplate(Objects.requireNonNull(factory.getObject()));
        return factory.getObject();// 返回SqlSessionFactory实例，用于创建SqlSession，使用SqlSession调用sql时不需要指定数据源，因为就在此处指定了
    }
    //如果要将 SqlSessionTemplate 作为单独的 Bean 注入，可以这样：
    @Bean(name = "sqlSessionTemplateOqc")
    public SqlSessionTemplate sqlSessionTemplateOqc(SqlSessionFactory sqlSessionFactoryOqc) {
        return new SqlSessionTemplate(sqlSessionFactoryOqc);
    }

    //qpost
    @Bean(name = "dataSourceQpost")
    @ConfigurationProperties(prefix = "spring.datasource.qpost")
    public DataSource dataSourceQpost() {
        return DataSourceBuilder.create().build();
    }
    @Bean(name = "jdbcTemplateQpost")
    public JdbcTemplate jdbcTemplateQpost(@Qualifier("dataSourceQpost") DataSource dataSource) {
        return new JdbcTemplate(dataSource);
    }
    @Bean(name = "sqlSessionFactoryQpost")
    public SqlSessionFactory sqlSessionFactoryQpost(@Qualifier("dataSourceQpost") DataSource dataSource) throws Exception {
        SqlSessionFactoryBean factory = new SqlSessionFactoryBean();// 创建SqlSessionFactoryBean实例
        factory.setDataSource(dataSource);// 设置数据源
        factory.setTypeAliasesPackage("com.epson.vipwp.domain");
        // 添加 SqlSessionTemplate Bean 的定义
        SqlSessionTemplate sqlSessionTemplate = new SqlSessionTemplate(Objects.requireNonNull(factory.getObject()));
        return factory.getObject();// 返回SqlSessionFactory实例，用于创建SqlSession，使用SqlSession调用sql时不需要指定数据源，因为就在此处指定了
    }
    //如果要将 SqlSessionTemplate 作为单独的 Bean 注入，可以这样：
    @Bean(name = "sqlSessionTemplateQpost")
    public SqlSessionTemplate sqlSessionTemplateQpost(SqlSessionFactory sqlSessionFactoryQpost) {
        return new SqlSessionTemplate(sqlSessionFactoryQpost);
    }

}

如果要使用jdbcTemplate，那么也需要在4个中添加@Primary，否则也会报错，不然就是使用哪个jdbc指明才行