解决Mybatis-plus高版本不向后兼容的问题

　　mybatis-plus插件后面的版本没有兼容低版本。即：不存在低版本中EntityWrapper这个类了。而该类采用数据库表真实字段名作查询条件，这样硬编码形式确实不友好，比如如果后面数据库表中字段更名那么所有涉及到的业务都需要去修改，且硬编码形式没有遵循orm映射框架的设计理念。所以mybatis-plus后面的版本已经不支持该类操作了。

　　但是这样造成一个问题。我们的一个项目开发设计时架构设计者采用了低版本的插件，但是项目进行一半时想要引入新版插件不兼容。要去一个个修改实在太麻烦，网上又没有这方面的文章。所以只能自己摸索出一个解决方案。

　　解决的第一步大家可以参考这篇文章：https://www.cnblogs.com/java-jun-world2099/articles/11114501.html

　　本以为就可以大功告成了，但是低高版本的插件内部设计重合度比较高（我并么有一步步去看原理），新的问题一个接一个。最后只能自己重写了BaseMapper和EntityWrapper这两个类。直接看代码好了：

application.yml

server:  port: 8088spring:  datasource:url: jdbc:mysql://xx.xx.xx.xxx:3306/ces?useUnicode=true&characterEncoding=utf-8useame: rootpassword: rootdriver-class-name: com.mysql.cj.jdbc.Drivertype: com.alibaba.druid.pool.DruidDataSourcemybatis-plus:  configuration:log-impl: org.apache.ibatis.logging.stdout.StdOutImpl  mapper-locations: classpath*:/mapper/*.xml

pom文件

<?xml version="1.0" encoding="UTF-8"?><project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>2.1.6.RELEASE</version><relativePath/></parent><groupId>com.bootjar</groupId><artifactId>shadeboot</artifactId><version>0.0.1-SNAPSHOT</version><name>shadeboot</name><description>Demo project for Spring Boot</description><properties><java.version>1.8</java.version></properties><dependencies><dependency><groupId>shadejar</groupId><artifactId>plusjar</artifactId><version>1.0</version></dependency><dependency><groupId>com.baomidou</groupId><artifactId>mybatis-plus-core</artifactId><version>3.1.1</version></dependency><!--<dependency><groupId>com.baomidou</groupId><artifactId>mybatis-plus-boot-starter</artifactId><version>3.1.1</version></dependency><dependency><groupId>com.baomidou</groupId><artifactId>mybatis-plus</artifactId><version>3.1.1</version></dependency>--><dependency><groupId>com.baomidou</groupId><artifactId>mybatisplus-spring-boot-starter</artifactId><version>1.0.5</version></dependency><dependency><groupId>com.baomidou</groupId><artifactId>mybatis-plus</artifactId><version>2.2.0</version></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.mybatis.spring.boot</groupId><artifactId>mybatis-spring-boot-starter</artifactId><version>2.0.1</version></dependency><dependency><groupId>com.alibaba</groupId><artifactId>druid</artifactId><version>1.1.6</version></dependency><!--lombok依赖--><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><optional>true</optional></dependency><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><scope>runtime</scope></dependency><dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-annotations</artifactId><version>2.9.7</version></dependency></dependencies><build><plugins><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId></plugin></plugins></build></project>

实体类User

@TableName("user")@Datapublic class User {@TableIdprivate Long id;private String userName;private Integer age;private String email;private Date birth;}

UserMapper接口

package com.bootjar.shadeboot.mapper;import com.bootjar.shadeboot.entity.BaseMapper;import com.bootjar.shadeboot.entity.User;import org.apache.ibatis.annotations.Mapper;/** * @author:shf date:2019/7/1 10:40 */@Mapperpublic interface UserMapper extends BaseMapper<User> {}

EntityWrapper

package com.bootjar.shadeboot.entity;import com.baomidou.mybatisplus.core.conditions.segments.MergeSegments;import com.baomidou.mybatisplus.core.conditions.segments.NormalSegmentList;import com.baomidou.mybatisplus.core.metadata.TableFieldInfo;import com.baomidou.mybatisplus.core.metadata.TableInfo;import com.baomidou.mybatisplus.core.toolkit.CollectionUtils;import com.baomidou.mybatisplus.core.toolkit.ReflectionKit;import com.baomidou.mybatisplus.core.toolkit.StringUtils;import com.baomidou.mybatisplus.core.toolkit.TableInfoHelper;import java.util.Objects;/** * @author:shf date:2019/7/1 14:13 */public class EntityWrapper<T> extends com.baomidou.mybatisplus.mapper.EntityWrapper<T> {public T entity;public MergeSegments expression;public String lastSql = "";@Overridepublic T getEntity() {retu this.entity;}@Overridepublic String getSqlSelect() {retu null;}public String getSqlSet() {retu null;}public MergeSegments getExpression() {retu this.expression;}public String getCustomSqlSegment() {MergeSegments expression = this.getExpression();if (Objects.nonNull(expression)) {NormalSegmentList normal = expression.getNormal();String sqlSegment = this.getSqlSegment();if (StringUtils.isNotEmpty(sqlSegment)) {if (normal.isEmpty()) {retu sqlSegment;}retu this.concatWhere(sqlSegment);}}retu "";}@Overridepublic String getSqlSegment() {String sqlSegment = "";String sqlWhere = "";if (this.expression != null) {sqlSegment = this.expression.getSqlSegment();} else if (this.sql != null) {sqlWhere = this.sql.toString();}if (StringUtils.isNotEmpty(sqlSegment)) {retu sqlSegment + this.lastSql;} else if (com.baomidou.mybatisplus.toolkit.StringUtils.isNotEmpty(sqlWhere)) {// retu this.isWhere != null ? (this.isWhere ? sqlWhere : sqlWhere.replaceFirst("WHERE", this.AND_OR)) : sqlWhere.replaceFirst("WHERE", this.AND_OR);retu sqlWhere;} else {retu StringUtils.isNotEmpty(this.lastSql) ? this.lastSql : null;}}private String concatWhere(String sql) {retu "WHERE " + sql;}@Overridepublic boolean isEmptyOfWhere() {retu this.isEmptyOfNormal() && this.isEmptyOfEntity();}public boolean nonEmptyOfWhere() {retu !this.isEmptyOfWhere();}public boolean isEmptyOfNormal() {if(this.getExpression() != null){retu CollectionUtils.isEmpty(this.getExpression().getNormal());}retu true;}public boolean nonEmptyOfNormal() {retu !this.isEmptyOfNormal();}public boolean nonEmptyOfEntity() {T entity = this.getEntity();if (entity == null) {retu false;} else {TableInfo tableInfo = TableInfoHelper.getTableInfo(entity.getClass());if (tableInfo == null) {retu false;} else if (tableInfo.getFieldList().stream().anyMatch((e) -> {retu this.fieldStrategyMatch(entity, e);})) {retu true;} else {retu StringUtils.isNotEmpty(tableInfo.getKeyProperty()) ? Objects.nonNull(ReflectionKit.getMethodValue(entity, tableInfo.getKeyProperty())) : false;}}}private boolean fieldStrategyMatch(T entity, TableFieldInfo e) {switch (e.getFieldStrategy()) {case NOT_NULL:retu Objects.nonNull(ReflectionKit.getMethodValue(entity, e.getProperty()));case IGNORED:retu true;case NOT_EMPTY:retu StringUtils.checkValNotNull(ReflectionKit.getMethodValue(entity, e.getProperty()));default:retu Objects.nonNull(ReflectionKit.getMethodValue(entity, e.getProperty()));}}public boolean isEmptyOfEntity() {retu !this.nonEmptyOfEntity();}}

BaseMapper

package com.bootjar.shadeboot.entity;import com.baomidou.mybatisplus.mapper.Wrapper;import org.apache.ibatis.annotations.Param;import org.apache.ibatis.session.RowBounds;import java.io.Serializable;import java.util.Collection;import java.util.List;import java.util.Map;/** * @author:shf date:2019/7/1 13:17 */public interface BaseMapper<T> extends com.baomidou.mybatisplus.core.mapper.BaseMapper<T> {int insert(T var1);Integer insertAllColumn(T var1);int deleteById(Serializable var1);int deleteByMap(@Param("cm") Map<String, Object> var1);Integer delete(@Param("ew") Wrapper<T> var1);int deleteBatchIds(@Param("coll") Collection<? extends Serializable> var1);int updateById(@Param("et") T var1);Integer updateAllColumnById(@Param("et") T var1);Integer update(@Param("et") T var1, @Param("ew") Wrapper<T> var2);T selectById(Serializable var1);List<T> selectBatchIds(@Param("coll") Collection<? extends Serializable> var1);List<T> selectByMap(@Param("cm") Map<String, Object> var1);T selectOne(@Param("ew") T var1);Integer selectCount(@Param("ew") Wrapper<T> var1);List<T> selectList(@Param("ew") Wrapper<T> var1);List<Map<String, Object>> selectMaps(@Param("ew") Wrapper<T> var1);List<Object> selectObjs(@Param("ew") Wrapper<T> var1);List<T> selectPage(RowBounds var1, @Param("ew") Wrapper<T> var2);List<Map<String, Object>> selectMapsPage(RowBounds var1, @Param("ew") Wrapper<T> var2);}

测试类ShadebootApplicationTests

package com.bootjar.shadeboot;import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;import com.bootjar.shadeboot.entity.EntityWrapper;import com.bootjar.shadeboot.entity.User;import com.bootjar.shadeboot.mapper.UserMapper;import org.junit.Test;import org.junit.runner.RunWith;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.boot.test.context.SpringBootTest;import org.springframework.test.context.junit4.SpringRunner;import java.util.HashMap;import java.util.List;import java.util.Map;@RunWith(SpringRunner.class)@SpringBootTestpublic class ShadebootApplicationTests {@Autowiredprivate UserMapper userMapper;//@Autowired//private UserCopyMapper userCopyMapper;@Testpublic void contextLoads() {User user = userMapper.selectById("1");System.out.println("--------------------user:" + user);EntityWrapper<User> itemWrapper = new EntityWrapper<>();itemWrapper.where("user_name = {0}", "Jack").eq("age", "20");List<User> itemsEntities = userMapper.selectList(itemWrapper);System.out.println("----------------itemsEntities :" + itemsEntities);LambdaQueryWrapper<User> queryWrapper = new LambdaQueryWrapper<User>().eq(User::getUserName, "Jack").last("ORDER BY id DESC");List<User> userList = userMapper.selectList(queryWrapper);System.out.println("----------------userList:" + userList);}@Testpublic void insertTest() {User user = new User();user.setUserName("dada");userMapper.insert(user);}@Testpublic void MapTest() {Map map = new HashMap();map.put("user_name", "1q");map.put("age", 18);List<User> MapList = userMapper.selectByMap(map);System.out.println("--------------------------MapList：" + MapList);}}

以上测试方法均通过，这是contextLoads方法的测试结果：

JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@7718a40f] will not be managed by Spring==>  Preparing: SELECT id,user_name,age,email,birth FROM user WHERE id=? ==> Parameters: 1(String)<==Columns: id, user_name, age, email, birth<==Row: 1, 1q, 18, test1@baomidou.com, 2019-01-01<==  Total: 1Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@397ef2]--------------------user:User(id=1, userName=1q, age=18, email=test1@baomidou.com, birth=Tue Jan 01 14:00:00 CST 2019)Creating a new SqlSessionSqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@1229a2b7] was not registered for synchronization because synchronization is not activeJDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@7718a40f] will not be managed by Spring==>  Preparing: SELECT id,user_name,age,email,birth FROM user WHERE (user_name = ? OR age = ?) ==> Parameters: Jack(String), 20(String)<==Columns: id, user_name, age, email, birth<==Row: 2, Jack, 20, test2@baomidou.com, 2019-01-01<==Row: 7, Jack, 24, test5@baomidou.com, 2019-01-01<==Row: 8, Jack, 24, test5@baomidou.com, 2019-01-01<==Row: 9, Jack, 24, test5@baomidou.com, 2019-01-01<==  Total: 4Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@1229a2b7]----------------itemsEntities :[User(id=2, userName=Jack, age=20, email=test2@baomidou.com, birth=Tue Jan 01 14:00:00 CST 2019), User(id=7, userName=Jack, age=24, email=test5@baomidou.com, birth=Tue Jan 01 14:00:00 CST 2019), User(id=8, userName=Jack, age=24, email=test5@baomidou.com, birth=Tue Jan 01 14:00:00 CST 2019), User(id=9, userName=Jack, age=24, email=test5@baomidou.com, birth=Tue Jan 01 14:00:00 CST 2019)]Creating a new SqlSessionSqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@4d95a72e] was not registered for synchronization because synchronization is not activeJDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@7718a40f] will not be managed by Spring==>  Preparing: SELECT id,user_name,age,email,birth FROM user WHERE user_name = ? AND ( age LIKE ? ) ORDER BY id DESC ==> Parameters: Jack(String), %24%(String)<==Columns: id, user_name, age, email, birth<==Row: 9, Jack, 24, test5@baomidou.com, 2019-01-01<==Row: 8, Jack, 24, test5@baomidou.com, 2019-01-01<==Row: 7, Jack, 24, test5@baomidou.com, 2019-01-01<==  Total: 3Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@4d95a72e]----------------userList:[User(id=9, userName=Jack, age=24, email=test5@baomidou.com, birth=Tue Jan 01 14:00:00 CST 2019), User(id=8, userName=Jack, age=24, email=test5@baomidou.com, birth=Tue Jan 01 14:00:00 CST 2019), User(id=7, userName=Jack, age=24, email=test5@baomidou.com, birth=Tue Jan 01 14:00:00 CST 2019)]2019-07-01 16:12:07.160  INFO 17744 --- [Thread-2] o.s.s.concurrent.ThreadPoolTaskExecutor  : Shutting down ExecutorService 'applicationTaskExecutor'2019-07-01 16:12:07.164  INFO 17744 --- [Thread-2] com.alibaba.druid.pool.DruidDataSource: {dataSource-1} closedProcess finished with exit code 0