mybatis plus 分页查询 left join 子查询参数无法找到报错

本文针对MyBatisPlus 3.4.1版本中在自定义分页SQL中使用LEFT JOIN时遇到的参数错误进行了详细解析,包括异常原因、解决方法,以及如何避免类似问题。

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问题

mybatis plus版本:3.4.1

SELECT
*
FROM a
LEFT JOIN ( SELECT * FROM b WHERE #{condition} ) b
.
.
.

在自定义分页SQL中进行letf join语句查询报错,假如有3个#{}参数,一个在left join中,最终会报java.sql.SQLException: Parameter index out of range 实际参数有3个,在SQL中只找到2个#{}

org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.type.TypeException: Could not set parameters for mapping: ParameterMapping{property='__frch_id_16', mode=IN, javaType=class java.lang.String, jdbcType=null, numericScale=null, resultMapId='null', jdbcTypeName='null', expression='null'}. Cause: org.apache.ibatis.type.TypeException: Error setting non null for parameter #18 with JdbcType null . Try setting a different JdbcType for this parameter or a different configuration property. Cause: java.sql.SQLException: Parameter index out of range (18 > number of parameters, which is 17).
	at org.mybatis.spring.MyBatisExceptionTranslator.translateExceptionIfPossible(MyBatisExceptionTranslator.java:92) ~[mybatis-spring-2.0.5.jar:2.0.5]
	at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:440) ~[mybatis-spring-2.0.5.jar:2.0.5]
	at com.sun.proxy.$Proxy156.selectList(Unknown Source) ~[na:na]
	at org.mybatis.spring.SqlSessionTemplate.selectList(SqlSessionTemplate.java:223) ~[mybatis-spring-2.0.5.jar:2.0.5]
	at com.baomidou.mybatisplus.core.override.MybatisMapperMethod.executeForIPage(MybatisMapperMethod.java:122) ~[mybatis-plus-core-3.4.1.jar:3.4.1]
	at com.baomidou.mybatisplus.core.override.MybatisMapperMethod.execute(MybatisMapperMethod.java:87) ~[mybatis-plus-core-3.4.1.jar:3.4.1]
	at com.baomidou.mybatisplus.core.override.MybatisMapperProxy$PlainMethodInvoker.invoke(MybatisMapperProxy.java:148) ~[mybatis-plus-core-3.4.1.jar:3.4.1]
	at com.baomidou.mybatisplus.core.override.MybatisMapperProxy.invoke(MybatisMapperProxy.java:89) ~[mybatis-plus-core-3.4.1.jar:3.4.1]
	at com.sun.proxy.$Proxy171.pageMyTask(Unknown Source) ~[na:na]
	at com.yango.discuz.service.impl.CmsTaskServiceImpl.pageMyTask(CmsTaskServiceImpl.java:246) ~[classes/:na]
	at com.yango.discuz.service.impl.CmsTaskServiceImpl$$FastClassBySpringCGLIB$$1.invoke(<generated>) ~[classes/:na]
	at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218) ~[spring-core-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:684) ~[spring-aop-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at com.yango.discuz.service.impl.CmsTaskServiceImpl$$EnhancerBySpringCGLIB$$1.pageMyTask(<generated>) ~[classes/:na]
	at com.yango.discuz.api.CmsTaskApi.pageMyTask(CmsTaskApi.java:108) ~[classes/:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_65]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_65]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_65]
	at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_65]
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:189) ~[spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:800) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1038) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) ~[spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) [spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:908) [spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:660) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882) [spring-webmvc-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) [tomcat-embed-websocket-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.springframework.boot.actuate.web.trace.servlet.HttpTraceFilter.doFilterInternal(HttpTraceFilter.java:90) [spring-boot-actuator-2.1.3.RELEASE.jar:2.1.3.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) [spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92) [spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93) [spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.springframework.session.web.http.SessionRepositoryFilter.doFilterInternal(SessionRepositoryFilter.java:151) [spring-session-core-2.1.4.RELEASE.jar:2.1.4.RELEASE]
	at org.springframework.session.web.http.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:81) [spring-session-core-2.1.4.RELEASE.jar:2.1.4.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.filterAndRecordMetrics(WebMvcMetricsFilter.java:117) [spring-boot-actuator-2.1.3.RELEASE.jar:2.1.3.RELEASE]
	at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.doFilterInternal(WebMvcMetricsFilter.java:106) [spring-boot-actuator-2.1.3.RELEASE.jar:2.1.3.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) [spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.1.5.RELEASE.jar:5.1.5.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at com.alibaba.csp.sentinel.adapter.servlet.CommonFilter.doFilter(CommonFilter.java:89) [sentinel-web-servlet-1.4.0.jar:na]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:200) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.StandardContextValve.__invoke(StandardContextValve.java:96) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:41002) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:834) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1415) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_65]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_65]
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.16.jar:9.0.16]
	at java.lang.Thread.run(Thread.java:745) [na:1.8.0_65]
Caused by: org.apache.ibatis.type.TypeException: Could not set parameters for mapping: ParameterMapping{property='__frch_id_16', mode=IN, javaType=class java.lang.String, jdbcType=null, numericScale=null, resultMapId='null', jdbcTypeName='null', expression='null'}. Cause: org.apache.ibatis.type.TypeException: Error setting non null for parameter #18 with JdbcType null . Try setting a different JdbcType for this parameter or a different configuration property. Cause: java.sql.SQLException: Parameter index out of range (18 > number of parameters, which is 17).
	at com.baomidou.mybatisplus.core.MybatisParameterHandler.setParameters(MybatisParameterHandler.java:215) ~[mybatis-plus-core-3.4.1.jar:3.4.1]
	at org.apache.ibatis.executor.statement.PreparedStatementHandler.parameterize(PreparedStatementHandler.java:94) ~[mybatis-3.5.6.jar:3.5.6]
	at org.apache.ibatis.executor.statement.RoutingStatementHandler.parameterize(RoutingStatementHandler.java:64) ~[mybatis-3.5.6.jar:3.5.6]
	at sun.reflect.GeneratedMethodAccessor334.invoke(Unknown Source) ~[na:na]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_65]
	at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_65]
	at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:63) ~[mybatis-3.5.6.jar:3.5.6]
	at com.sun.proxy.$Proxy261.parameterize(Unknown Source) ~[na:na]
	at com.baomidou.mybatisplus.core.executor.MybatisSimpleExecutor.prepareStatement(MybatisSimpleExecutor.java:99) ~[mybatis-plus-core-3.4.1.jar:3.4.1]
	at com.baomidou.mybatisplus.core.executor.MybatisSimpleExecutor.doQuery(MybatisSimpleExecutor.java:68) ~[mybatis-plus-core-3.4.1.jar:3.4.1]
	at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:325) ~[mybatis-3.5.6.jar:3.5.6]
	at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156) ~[mybatis-3.5.6.jar:3.5.6]
	at com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor.willDoQuery(PaginationInnerInterceptor.java:134) ~[mybatis-plus-extension-3.4.1.jar:3.4.1]
	at com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor.intercept(MybatisPlusInterceptor.java:59) ~[mybatis-plus-extension-3.4.1.jar:3.4.1]
	at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:61) ~[mybatis-3.5.6.jar:3.5.6]
	at com.sun.proxy.$Proxy260.query(Unknown Source) ~[na:na]
	at com.github.pagehelper.PageInterceptor.intercept(PageInterceptor.java:143) ~[pagehelper-5.1.2.jar:na]
	at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:61) ~[mybatis-3.5.6.jar:3.5.6]
	at com.sun.proxy.$Proxy260.query(Unknown Source) ~[na:na]
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:147) ~[mybatis-3.5.6.jar:3.5.6]
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:140) ~[mybatis-3.5.6.jar:3.5.6]
	at sun.reflect.GeneratedMethodAccessor335.invoke(Unknown Source) ~[na:na]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_65]
	at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_65]
	at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:426) ~[mybatis-spring-2.0.5.jar:2.0.5]
	... 84 common frames omitted
Caused by: org.apache.ibatis.type.TypeException: Error setting non null for parameter #18 with JdbcType null . Try setting a different JdbcType for this parameter or a different configuration property. Cause: java.sql.SQLException: Parameter index out of range (18 > number of parameters, which is 17).
	at org.apache.ibatis.type.BaseTypeHandler.setParameter(BaseTypeHandler.java:75) ~[mybatis-3.5.6.jar:3.5.6]
	at com.baomidou.mybatisplus.core.MybatisParameterHandler.setParameters(MybatisParameterHandler.java:213) ~[mybatis-plus-core-3.4.1.jar:3.4.1]
	... 108 common frames omitted
Caused by: java.sql.SQLException: Parameter index out of range (18 > number of parameters, which is 17).
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129) ~[mysql-connector-java-8.0.15.jar:8.0.15]
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97) ~[mysql-connector-java-8.0.15.jar:8.0.15]
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:89) ~[mysql-connector-java-8.0.15.jar:8.0.15]
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:63) ~[mysql-connector-java-8.0.15.jar:8.0.15]
	at com.mysql.cj.jdbc.ClientPreparedStatement.checkBounds(ClientPreparedStatement.java:1402) ~[mysql-connector-java-8.0.15.jar:8.0.15]
	at com.mysql.cj.jdbc.ClientPreparedStatement.getCoreParameterIndex(ClientPreparedStatement.java:1415) ~[mysql-connector-java-8.0.15.jar:8.0.15]
	at com.mysql.cj.jdbc.ClientPreparedStatement.setString(ClientPreparedStatement.java:1782) ~[mysql-connector-java-8.0.15.jar:8.0.15]
	at com.alibaba.druid.pool.DruidPooledPreparedStatement.setString(DruidPooledPreparedStatement.java:369) ~[druid-1.1.14.jar:1.1.14]
	at sun.reflect.GeneratedMethodAccessor307.invoke(Unknown Source) ~[na:na]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_65]
	at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_65]
	at org.apache.ibatis.logging.jdbc.PreparedStatementLogger.invoke(PreparedStatementLogger.java:67) ~[mybatis-3.5.6.jar:3.5.6]
	at com.sun.proxy.$Proxy263.setString(Unknown Source) ~[na:na]
	at org.apache.ibatis.type.StringTypeHandler.setNonNullParameter(StringTypeHandler.java:31) ~[mybatis-3.5.6.jar:3.5.6]
	at org.apache.ibatis.type.StringTypeHandler.setNonNullParameter(StringTypeHandler.java:26) ~[mybatis-3.5.6.jar:3.5.6]
	at org.apache.ibatis.type.BaseTypeHandler.setParameter(BaseTypeHandler.java:73) ~[mybatis-3.5.6.jar:3.5.6]
	... 109 common frames omitted

解决方式

查找了mybatis plus官方文档和github上的问答,得到了几个解决方法

MyBatis-Plus是一个基于MyBatis的增强工具,提供了许多便捷的功能来简化开发。其中,MyBatis-Plus-joinMyBatis-Plus的一个扩展模块,用于支持关联查询。 在使用MyBatis-join的依赖。可以在项目的pom.xml文件中添加如下依赖: ```xml <dependency> <groupId>com.baomidou</groupId> <artifactId>mybatis-plus-extension</artifactId> <version>3.4.3.1</version> </dependency> ``` 2. 在实体类中定义关联关系。使用MyBatis-Plus-join时,需要在实体类中定义关联关系,可以使用`@TableField`注解来指定关联字段。例如: ```java public class User { private Long id; private String name; @TableField(exist = false) private List<Role> roles; // getter and setter } public class Role { private Long id; private String roleName; // getter and setter } ``` 3. 编写Mapper接口。在Mapper接口中,可以使用`@Select`注解来编写关联查询的SQL语句。例如: ```java @Mapper public interface UserMapper extends BaseMapper<User> { @Select("SELECT u.*, r.* FROM user u LEFT JOIN user_role ur ON u.id = ur.user_id LEFT JOIN role r ON ur.role_id = r.id") @Results({ @Result(property = "id", column = "id"), @Result(property = "name", column = "name"), @Result(property = "roles", column = "id", many = @Many(select = "com.example.mapper.RoleMapper.selectByUserId")) }) List<User> selectUserWithRoles(Page<User> page); } ``` 4. 编写关联查询的子查询。在上面的例子中,使用了`@Many`注解来指定关联查询的子查询方法。例如: ```java @Mapper public interface RoleMapper extends BaseMapper<Role> { @Select("SELECT r.* FROM role r LEFT JOIN user_role ur ON r.id = ur.role_id WHERE ur.user_id = #{userId}") List<Role> selectByUserId(Long userId); } ``` 5. 调用分页查询方法。在Service层或者Controller层中,可以调用Mapper接口中定义的分页查询方法来进行查询。例如: ```java @Service public class UserServiceImpl implements UserService { @Autowired private UserMapper userMapper; @Override public IPage<User> getUserWithRoles(Page<User> page) { return userMapper.selectUserWithRoles(page); } } ``` 以上就是使用MyBatis-Plus-join进行分页查询的基本步骤。通过定义关联关系和编写关联查询的SQL语句,可以方便地进行关联查询并实现分页功能。
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