• Mybatis-plus

    在有Mybatis基础的情况下，再去接触Mybatis-plus，就容易的多

    先就我现在使用情况讲讲，我眼中，它跟Mybatis啥区别吧。

    作为Mybatis的升级版，它除了具备Mybatis本身就有的功能之外，还增加了通过lambda表达式操作数据库，以及逻辑删除标识等功能

    1.引入依赖

    1.         <dependency>
    2.             <groupId>com.baomidougroupId>
    3.             <artifactId>mybatis-plus-boot-starterartifactId>
    4.             <optional>trueoptional>
    5.         dependency>

    2.通过数据库中的表反向生成mapper,实体等

    2.1在idea中建立数据库连接

    2.2安装MybatisX-Generator插件

    2.3选中表，右键通过MybatisX-Generator插件去生成实体，mapper，甚至service的接口实现类都能生出来

    IDEA插件之mybatisx 插件使用教程_idea mybatis插件_IT小悟的博客-CSDN博客

    下边能看到service也能生出来，生出来的service中也自动引入了mapper 

     

    3.service调用

    3.1 生成的service长这样

    自动继承了一个ServiceImpl，这个ServiceImpl是Mybatis-Plus提供的

    1. @Service
    2. public class SysDataSourceConfigServiceImpl extends ServiceImpl
    3.     implements SysDataSourceConfigService{
    4.  
    5. }

    3.2 service中如何使用

    Mybatis-plus给生成的service都提供了一个公共父类，就是上边的

    ServiceImpl

    这里边有很多泛型方法，所以继承的时候指定mapper和entity之后，就可以直接调用一些现成的方法，不需要自己再去实现

    我现在一般比较常用的是

    getById(通过id查询)

    saveOrUpdate(根据id是否存在去走新增方法或者保存方法)

    updateById(但是mybatis在update的时候，不会更新空字段，如果有些情况你不希望这个字段被修改，直接在业务代码里把他置为空即可)

    我把Mybatis-plus的class文件直接贴上来了 

    1. //
    2. // Source code recreated from a .class file by IntelliJ IDEA
    3. // (powered by FernFlower decompiler)
    4. //
    5.  
    6. package com.baomidou.mybatisplus.extension.service.impl;
    7.  
    8. import com.baomidou.mybatisplus.core.conditions.Wrapper;
    9. import com.baomidou.mybatisplus.core.enums.SqlMethod;
    10. import com.baomidou.mybatisplus.core.mapper.BaseMapper;
    11. import com.baomidou.mybatisplus.core.metadata.TableInfo;
    12. import com.baomidou.mybatisplus.core.metadata.TableInfoHelper;
    13. import com.baomidou.mybatisplus.core.toolkit.Assert;
    14. import com.baomidou.mybatisplus.core.toolkit.CollectionUtils;
    15. import com.baomidou.mybatisplus.core.toolkit.GlobalConfigUtils;
    16. import com.baomidou.mybatisplus.core.toolkit.ReflectionKit;
    17. import com.baomidou.mybatisplus.core.toolkit.StringUtils;
    18. import com.baomidou.mybatisplus.extension.service.IService;
    19. import com.baomidou.mybatisplus.extension.toolkit.SqlHelper;
    20. import java.io.Serializable;
    21. import java.util.Collection;
    22. import java.util.Map;
    23. import java.util.Objects;
    24. import java.util.function.BiConsumer;
    25. import java.util.function.Consumer;
    26. import java.util.function.Function;
    27. import org.apache.ibatis.binding.MapperMethod;
    28. import org.apache.ibatis.logging.Log;
    29. import org.apache.ibatis.logging.LogFactory;
    30. import org.apache.ibatis.session.SqlSession;
    31. import org.mybatis.spring.SqlSessionUtils;
    32. import org.springframework.beans.factory.annotation.Autowired;
    33. import org.springframework.transaction.annotation.Transactional;
    34.  
    35. public class ServiceImplextends BaseMapper, T> implements IService {
    36.     protected Log log = LogFactory.getLog(this.getClass());
    37.     @Autowired
    38.     protected M baseMapper;
    39.     protected Class entityClass = this.currentModelClass();
    40.     protected Class mapperClass = this.currentMapperClass();
    41.  
    42.     public ServiceImpl() {
    43.     }
    44.  
    45.     public M getBaseMapper() {
    46.         return this.baseMapper;
    47.     }
    48.  
    49.     public Class getEntityClass() {
    50.         return this.entityClass;
    51.     }
    52.  
    53.     /** @deprecated */
    54.     @Deprecated
    55.     protected boolean retBool(Integer result) {
    56.         return SqlHelper.retBool(result);
    57.     }
    58.  
    59.     protected Class currentMapperClass() {
    60.         return ReflectionKit.getSuperClassGenericType(this.getClass(), ServiceImpl.class, 0);
    61.     }
    62.  
    63.     protected Class currentModelClass() {
    64.         return ReflectionKit.getSuperClassGenericType(this.getClass(), ServiceImpl.class, 1);
    65.     }
    66.  
    67.     /** @deprecated */
    68.     @Deprecated
    69.     protected SqlSession sqlSessionBatch() {
    70.         return SqlHelper.sqlSessionBatch(this.entityClass);
    71.     }
    72.  
    73.     /** @deprecated */
    74.     @Deprecated
    75.     protected void closeSqlSession(SqlSession sqlSession) {
    76.         SqlSessionUtils.closeSqlSession(sqlSession, GlobalConfigUtils.currentSessionFactory(this.entityClass));
    77.     }
    78.  
    79.     /** @deprecated */
    80.     @Deprecated
    81.     protected String sqlStatement(SqlMethod sqlMethod) {
    82.         return SqlHelper.table(this.entityClass).getSqlStatement(sqlMethod.getMethod());
    83.     }
    84.  
    85.     @Transactional(
    86.         rollbackFor = {Exception.class}
    87.     )
    88.     public boolean saveBatch(Collection entityList, int batchSize) {
    89.         String sqlStatement = this.getSqlStatement(SqlMethod.INSERT_ONE);
    90.         return this.executeBatch(entityList, batchSize, (sqlSession, entity) -> {
    91.             sqlSession.insert(sqlStatement, entity);
    92.         });
    93.     }
    94.  
    95.     protected String getSqlStatement(SqlMethod sqlMethod) {
    96.         return SqlHelper.getSqlStatement(this.mapperClass, sqlMethod);
    97.     }
    98.  
    99.     @Transactional(
    100.         rollbackFor = {Exception.class}
    101.     )
    102.     public boolean saveOrUpdate(T entity) {
    103.         if (null == entity) {
    104.             return false;
    105.         } else {
    106.             TableInfo tableInfo = TableInfoHelper.getTableInfo(this.entityClass);
    107.             Assert.notNull(tableInfo, "error: can not execute. because can not find cache of TableInfo for entity!", new Object[0]);
    108.             String keyProperty = tableInfo.getKeyProperty();
    109.             Assert.notEmpty(keyProperty, "error: can not execute. because can not find column for id from entity!", new Object[0]);
    110.             Object idVal = tableInfo.getPropertyValue(entity, tableInfo.getKeyProperty());
    111.             return !StringUtils.checkValNull(idVal) && !Objects.isNull(this.getById((Serializable)idVal)) ? this.updateById(entity) : this.save(entity);
    112.         }
    113.     }
    114.  
    115.     @Transactional(
    116.         rollbackFor = {Exception.class}
    117.     )
    118.     public boolean saveOrUpdateBatch(Collection entityList, int batchSize) {
    119.         TableInfo tableInfo = TableInfoHelper.getTableInfo(this.entityClass);
    120.         Assert.notNull(tableInfo, "error: can not execute. because can not find cache of TableInfo for entity!", new Object[0]);
    121.         String keyProperty = tableInfo.getKeyProperty();
    122.         Assert.notEmpty(keyProperty, "error: can not execute. because can not find column for id from entity!", new Object[0]);
    123.         return SqlHelper.saveOrUpdateBatch(this.entityClass, this.mapperClass, this.log, entityList, batchSize, (sqlSession, entity) -> {
    124.             Object idVal = tableInfo.getPropertyValue(entity, keyProperty);
    125.             return StringUtils.checkValNull(idVal) || CollectionUtils.isEmpty(sqlSession.selectList(this.getSqlStatement(SqlMethod.SELECT_BY_ID), entity));
    126.         }, (sqlSession, entity) -> {
    127.             MapperMethod.ParamMap param = new MapperMethod.ParamMap();
    128.             param.put("et", entity);
    129.             sqlSession.update(this.getSqlStatement(SqlMethod.UPDATE_BY_ID), param);
    130.         });
    131.     }
    132.  
    133.     @Transactional(
    134.         rollbackFor = {Exception.class}
    135.     )
    136.     public boolean updateBatchById(Collection entityList, int batchSize) {
    137.         String sqlStatement = this.getSqlStatement(SqlMethod.UPDATE_BY_ID);
    138.         return this.executeBatch(entityList, batchSize, (sqlSession, entity) -> {
    139.             MapperMethod.ParamMap param = new MapperMethod.ParamMap();
    140.             param.put("et", entity);
    141.             sqlSession.update(sqlStatement, param);
    142.         });
    143.     }
    144.  
    145.     public T getOne(Wrapper queryWrapper, boolean throwEx) {
    146.         return throwEx ? this.baseMapper.selectOne(queryWrapper) : SqlHelper.getObject(this.log, this.baseMapper.selectList(queryWrapper));
    147.     }
    148.  
    149.     public Map getMap(Wrapper queryWrapper) {
    150.         return (Map)SqlHelper.getObject(this.log, this.baseMapper.selectMaps(queryWrapper));
    151.     }
    152.  
    153.     public  V getObj(Wrapper queryWrapper, Functionsuper Object, V> mapper) {
    154.         return SqlHelper.getObject(this.log, this.listObjs(queryWrapper, mapper));
    155.     }
    156.  
    157.     /** @deprecated */
    158.     @Deprecated
    159.     protected boolean executeBatch(Consumer consumer) {
    160.         return SqlHelper.executeBatch(this.entityClass, this.log, consumer);
    161.     }
    162.  
    163.     protected  boolean executeBatch(Collection list, int batchSize, BiConsumer consumer) {
    164.         return SqlHelper.executeBatch(this.entityClass, this.log, list, batchSize, consumer);
    165.     }
    166.  
    167.     protected  boolean executeBatch(Collection list, BiConsumer consumer) {
    168.         return this.executeBatch(list, 1000, consumer);
    169.     }
    170. }

    上代码 

    4.Mapper使用

    4.1 生成的Mapper长这样

    1. @Mapper//这个我好像是自己加上去的
    2. public interface SysGroupMapper extends BaseMapper {
    3.  
    4. }

    4.2 BaseMapper的使用 

    Mybatis-plus不光在ServiceImpl中通过泛型提供了很多基础的方法

    也在BaseMapper中通过泛型，提供了很多方法

    我一般用的比较多的

    this.baseMapper.selectBatchIds(collect);
    this.baseMapper.selectList(new LambdaQueryWrapper().in(SysGroup::getId, groupIds).select(SysGroup::getGroupName));

    直接贴上Mybatis-plus自带的BaseMapper代码

    1. //
    2. // Source code recreated from a .class file by IntelliJ IDEA
    3. // (powered by FernFlower decompiler)
    4. //
    5.  
    6. package com.baomidou.mybatisplus.core.mapper;
    7.  
    8. import com.baomidou.mybatisplus.core.conditions.Wrapper;
    9. import com.baomidou.mybatisplus.core.metadata.IPage;
    10. import com.baomidou.mybatisplus.core.toolkit.CollectionUtils;
    11. import com.baomidou.mybatisplus.core.toolkit.ExceptionUtils;
    12. import java.io.Serializable;
    13. import java.util.Collection;
    14. import java.util.List;
    15. import java.util.Map;
    16. import org.apache.ibatis.annotations.Param;
    17.  
    18. public interface BaseMapper extends Mapper {
    19.     int insert(T entity);
    20.  
    21.     int deleteById(Serializable id);
    22.  
    23.     int deleteById(T entity);
    24.  
    25.     int deleteByMap(@Param("cm") Map columnMap);
    26.  
    27.     int delete(@Param("ew") Wrapper queryWrapper);
    28.  
    29.     int deleteBatchIds(@Param("coll") Collection idList);
    30.  
    31.     int updateById(@Param("et") T entity);
    32.  
    33.     int update(@Param("et") T entity, @Param("ew") Wrapper updateWrapper);
    34.  
    35.     T selectById(Serializable id);
    36.  
    37.     List selectBatchIds(@Param("coll") Collection idList);
    38.  
    39.     List selectByMap(@Param("cm") Map columnMap);
    40.  
    41.     default T selectOne(@Param("ew") Wrapper queryWrapper) {
    42.         List ts = this.selectList(queryWrapper);
    43.         if (CollectionUtils.isNotEmpty(ts)) {
    44.             if (ts.size() != 1) {
    45.                 throw ExceptionUtils.mpe("One record is expected, but the query result is multiple records", new Object[0]);
    46.             } else {
    47.                 return ts.get(0);
    48.             }
    49.         } else {
    50.             return null;
    51.         }
    52.     }
    53.  
    54.     Long selectCount(@Param("ew") Wrapper queryWrapper);
    55.  
    56.     List selectList(@Param("ew") Wrapper queryWrapper);
    57.  
    58.     List> selectMaps(@Param("ew") Wrapper queryWrapper);
    59.  
    60.     List selectObjs(@Param("ew") Wrapper queryWrapper);
    61.  
    62.     
      extends IPage> P selectPage(P page, @Param("ew") Wrapper queryWrapper);
    63.  
    64.     
      extends IPage>> P selectMapsPage(P page, @Param("ew") Wrapper queryWrapper);
    65. }
      66.  

      贴一段代码 
       

       
       

      4.3正常使用mapper
       

       

      5.lambda表达式
       

      1. List sysGroups = this.baseMapper.selectList(new LambdaQueryWrapper().in(SysGroup::getId, groupIds).select(SysGroup::getGroupName));
      2.  
      3. sysUserGroupMapper.delete(new LambdaQueryWrapper().eq(SysUserGroup::getUserName,username));
      4.  
      5.  List list = sysUserService.list(new LambdaQueryWrapper().in(SysUser::getId, userIdList).select(SysUser::getUsername));
      6.  
      7. List list = this.list(new LambdaQueryWrapper().ne(id != null, SysGroup::getId, id).eq(SysGroup::getGroupName, groupName));
      8.  
      9.   boolean result = this.update(new LambdaUpdateWrapper()
      10.                 .eq(SysMenu::getId, menuId)
      11.                 .set(SysMenu::getVisible, status)
      12.         );
       

      6.实体注解
       

      
                
                    
                

                
    66. 

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      67. 
                
    67. 
                    原文地址：https://blog.csdn.net/qq_35653822/article/details/133817207
                
      68.