Mybatis-Plus 的简单使用

清疚 2022-12-05 15:16 168阅读 0赞

## 1.1 简介 ##

### 1.1.1 概述 ###

MyBatis-Plus(简称 MP)是一个 MyBatis 的增强工具，在 MyBatis 的基础上只做增强不做改变，为简化开发、提高效率而生。在不用编写任何 SQL 语句的情况下即可以极其方便的实现单一、批量、分页等操作。MyBatis-Plus 的增强，其实就是在 MyBatis 的基础上进行了自己的封装和拓展，可以让使用者不写 xml 文件，只需简单配置，即可快速进行 CRUD 操作，从而节省大量时间，简化了开发。

![在这里插入图片描述][20200911091956515.png_pic_center]

### 1.1.2 相关依赖 ###

<dependency>
        <groupId>com.baomidou</groupId>
        <artifactId>mybatis-plus</artifactId>
        <version>3.4.0</version>
    </dependency>

## 1.2 简单使用 ##

### 1.2.1 配置 ###

**☞ Mybatis 的配置**

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"></property>
        
        <property name="configLocation" value="classpath:mybatis.xml"></property>
    </bean>
    
    
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.software.ssm.mapper"></property>
    </bean>

**☞ Mybatis-Plus 的配置**

<bean id="sqlSessionFactory" class="com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"></property>
        
        <property name="configLocation" value="classpath:mybatis.xml"></property>
    </bean>
    
    
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.software.ssm.mapper"></property>
    </bean>

### 1.2.2 常用注解 ###

<table> 
 <thead> 
  <tr> 
   <th align="left">注解</th> 
   <th align="left">说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left">@TableName</td> 
   <td align="left">描述：表名注解<br>属性：value ☞ 表名<br>   schema ☞ schema<br>   keepGlobalPrefix ☞ 是否保持使用全局的 tablePrefix 的值，默认值 false(如果设置了全局 tablePrefix 且自行设置了 value 的值)<br>   resultMap ☞ xml 中 resultMap 的 id<br>   autoResultMap ☞ 是否自动构建 resultMap 并使用，默认值 false(如果设置 resultMap 则不会进行 resultMap 的自动构建并注入)</td> 
  </tr> 
  <tr> 
   <td align="left">@TableId</td> 
   <td align="left">描述：主键注解<br>属性：value ☞ 主键字段名<br>   type ☞ 主键类型，默认值 IdType.NONE<br>    AUTO：数据库ID自增<br>    NONE：无状态,该类型为未设置主键类型(注解里等于跟随全局，全局里约等于 INPUT)<br>    INPUT：insert 前自行 set 主键值<br>    ASSIGN_ID：分配ID(主键类型为 Number 或 String，使用接口 IdentifierGenerator 的方法 nextId (默认雪花算法)<br>    ASSIGN_UUID：分配 UUID，主键类型为 String，使用接口 IdentifierGenerator 的方法 nextUUID(默认 default 方法)</td> 
  </tr> 
  <tr> 
   <td align="left">@TableField</td> 
   <td align="left">描述：字段注解(非主键)<br>属性：value ☞ 数据库字段名<br>   el ☞ 映射为原生 #{ … } 逻辑,相当于写在 xml 里的 #{ … } 部分<br>   exist ☞ 是否为数据库表字段，默认 true<br>   condition ☞ 字段 where 实体查询比较条件，有值设置则按设置的值为准，没有则为默认全局的 %s=#{%s}<br>   update ☞ 字段 update set 部分注入, 例如：update="%s+1" 表示更新时会 set version=version+1(该属性优先级高于 el 属性)<br>   select ☞ 是否进行 select 查询，默认 true<br>   keepGlobalFormat ☞ 是否保持使用全局的 format 进行处理，默认 false<br>   jdbcType ☞ JDBC 类型，默认 JdbcType.UNDEFINED (该默认值不代表会按照该值生效)<br>   typeHandler ☞ 类型处理器，默认 UnknownTypeHandler.class (该默认值不代表会按照该值生效)<br>   numericScale ☞ 指定小数点后保留的位数</td> 
  </tr> 
 </tbody> 
</table>

### 1.2.3 实体类 ###

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 实体类 */
    @Data // Lombok 注解
    public class Student { 
    	@TableId
        private Long id;
        private String name;
        private Integer age;
    }

### 1.2.4 mapper ###

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 数据访问层接口，继承 Mybatis-Plus 的 BaseMapper<T> */
    @Repository
    public interface StudentMapper extends BaseMapper<Student> { }

### 1.2.5 测试 ###

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 测试类 */
    @SpringJUnitConfig(locations = "classpath:application.xml")
    public class Demo { 
    
        @Autowired
        private StudentMapper studentMapper;
    
        @Test
        public void TestSelect() { 
            List<Student> students = studentMapper.selectList(null);
            System.out.println(students);
        }
    }

![在这里插入图片描述][20200911105430114.png_pic_center]

## 1.3 通用 CRUD ##

![在这里插入图片描述][20200911140020382.png_pic_center]

### 1.3.1 插入操作 ###

**☞ int insert(T entity)**

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 插入操作 */
    @SpringJUnitConfig(locations = "classpath:application.xml")
    public class Demo { 
    
        @Autowired
        private StudentMapper studentMapper;
    
        @Test
        public void TestInsert() { 
            Student student = new Student();
            student.setName("大锤");
            student.setAge(800);
    
            studentMapper.insert(student);
            System.out.println(student);
        }
    }

![在这里插入图片描述][20200911140450395.png_pic_center]  
  咱们可以看到自动生成的主键是一个不知道是啥的数字，这个是应为我们没有设置主键增长类型，我们再实体类中使用 `@TableId(type = IdType.AUTO)` 设置为自动增长即可

![在这里插入图片描述][20200911141127786.png_pic_center]

### 1.3.2 更新操作 ###

**☞ int updateById(@Param(“et”) T entity)**

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 根据 id 修改 */
    @SpringJUnitConfig(locations = "classpath:application.xml")
    public class Demo { 
    
        @Autowired
        private StudentMapper studentMapper;
    
        @Test
        public void TestUpdate() { 
            Student student = new Student();
            student.setId(1L);
            student.setName("姬发");
    
            int i = studentMapper.updateById(student);
            System.out.println("影响的行数：" + i);
        }
    }

![在这里插入图片描述][2020091114213758.png_pic_center]

**☞ int update(@Param(“et”) T entity, @Param(“ew”) Wrapper<T> updateWrapper)**

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 根据条件更新 */
    @SpringJUnitConfig(locations = "classpath:application.xml")
    public class Demo { 
    
        @Autowired
        private StudentMapper studentMapper;
    
        @Test
        public void TestUpdate() { 
            Student student = new Student();
            student.setAge(900);
    
            QueryWrapper<Student> studentQueryWrapper = new QueryWrapper<Student>();
            studentQueryWrapper.eq("name", "姬发");
    
            int i = studentMapper.update(student, studentQueryWrapper);
            System.out.println("影响的行数：" + i);
        }
    }

![在这里插入图片描述][20200911142458598.png_pic_center]

### 1.3.3 删除操作 ###

**☞ int deleteById(Serializable id)**

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 根据 id 删除 */
    @SpringJUnitConfig(locations = "classpath:application.xml")
    public class Demo { 
    
        @Autowired
        private StudentMapper studentMapper;
    
        @Test
        public void TestDel() { 
            int i = studentMapper.deleteById(1L);
            System.out.println("影响的行数：" + i);
        }
    }

![在这里插入图片描述][20200911142721552.png_pic_center]

**☞ int deleteByMap(@Param(“cm”) Map<String, Object> columnMap)**

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 根据 Map 中的条件删除，为空则删除所有 */
    @SpringJUnitConfig(locations = "classpath:application.xml")
    public class Demo { 
    
        @Autowired
        private StudentMapper studentMapper;
    
        @Test
        public void TestDel() { 
            Map<String, Object> columnMap = new HashMap<>();
            columnMap.put("name", "张良");
            columnMap.put("age", 200);
    
            int i = studentMapper.deleteByMap(columnMap);
            System.out.println("影响的行数：" + i);
        }
    }

![在这里插入图片描述][20200911143436686.png_pic_center]

**☞ int delete(@Param(“ew”) Wrapper<T> wrapper)**

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 根据条件删除 */
    @SpringJUnitConfig(locations = "classpath:application.xml")
    public class Demo { 
    
        @Autowired
        private StudentMapper studentMapper;
    
        @Test
        public void TestDel() { 
            QueryWrapper<Student> studentQueryWrapper = new QueryWrapper<>();
            // 可以使用链式编程
            studentQueryWrapper.eq("age", 280);
            studentQueryWrapper.like("name", "李");
    
            int i = studentMapper.delete(studentQueryWrapper);
            System.out.println("影响的行数：" + i);
        }
    }

![在这里插入图片描述][20200911143828435.png_pic_center]

**☞ int deleteBatchIds(@Param(“coll”) Collection<? extends Serializable> idList)**

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 根据 id 批量删除 */
    @SpringJUnitConfig(locations = "classpath:application.xml")
    public class Demo { 
    
        @Autowired
        private StudentMapper studentMapper;
    
        @Test
        public void TestDel() { 
            List<Long> list = new ArrayList<>();
            list.add(7L);
            list.add(8L);
            list.add(9L);
    
            int i = studentMapper.deleteBatchIds(list);
            System.out.println("影响的行数：" + i);
        }
    }

![在这里插入图片描述][20200911144120817.png_pic_center]

### 1.3.4 查询操作 ###

**☞ T selectById(Serializable id)**

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 根据 id 查询 */
    @SpringJUnitConfig(locations = "classpath:application.xml")
    public class Demo { 
    
        @Autowired
        private StudentMapper studentMapper;
    
        @Test
        public void TestSelect() { 
            Student student = studentMapper.selectById(10L);
            System.out.println(student);
        }
    }

![在这里插入图片描述][20200911163556793.png_pic_center]

**☞ List selectBatchIds(@Param(“coll”) Collection<? extends Serializable> idList)**

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 根据 id 批量查询，参数不能为空 */
    @SpringJUnitConfig(locations = "classpath:application.xml")
    public class Demo { 
    
        @Autowired
        private StudentMapper studentMapper;
    
        @Test
        public void TestSelect() { 
            List<Long> list = new ArrayList<>();
            list.add(10L);
            list.add(11L);
    
            List<Student> students = studentMapper.selectBatchIds(list);
            System.out.println(students);
        }
    }

![在这里插入图片描述][20200911163931982.png_pic_center]

**☞ List selectByMap(@Param(“cm”) Map<String, Object> columnMap)**

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 根据 Map 查询 */
    @SpringJUnitConfig(locations = "classpath:application.xml")
    public class Demo { 
    
        @Autowired
        private StudentMapper studentMapper;
    
        @Test
        public void TestSelect() { 
            HashMap<String, Object> columnMap = new HashMap<>();
            columnMap.put("name", "张良");
    
            List<Student> students = studentMapper.selectByMap(columnMap);
            System.out.println(students);
        }
    }

![在这里插入图片描述][20200911164219729.png_pic_center]

**☞ T selectOne(@Param(“ew”) Wrapper<T> queryWrapper)**

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 根据条件查询一条数据 */
    @SpringJUnitConfig(locations = "classpath:application.xml")
    public class Demo { 
    
        @Autowired
        private StudentMapper studentMapper;
    
        @Test
        public void TestSelect() { 
            QueryWrapper<Student> studentQueryWrapper = new QueryWrapper<>();
            studentQueryWrapper.eq("id", 10L);
    
            Student student = studentMapper.selectOne(studentQueryWrapper);
            System.out.println(student);
        }
    }

![在这里插入图片描述][20200911164626504.png_pic_center]

**☞ List selectList(@Param(“ew”) Wrapper<T> queryWrapper)**

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 根据条件查询 */
    @SpringJUnitConfig(locations = "classpath:application.xml")
    public class Demo { 
    
        @Autowired
        private StudentMapper studentMapper;
    
        @Test
        public void TestSelect() { 
            QueryWrapper<Student> studentQueryWrapper = new QueryWrapper<>();
            studentQueryWrapper.like("name", "左");
    
            List<Student> students = studentMapper.selectList(studentQueryWrapper);
            System.out.println(students);
        }
    }

![在这里插入图片描述][20200911164815452.png_pic_center]

**☞ Integer selectCount(@Param(“ew”) Wrapper<T> queryWrapper)**

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 统计符合条件的数据 */
    @SpringJUnitConfig(locations = "classpath:application.xml")
    public class Demo { 
    
        @Autowired
        private StudentMapper studentMapper;
    
        @Test
        public void TestSelect() { 
            QueryWrapper<Student> studentQueryWrapper = new QueryWrapper<>();
            studentQueryWrapper.like("name", "左");
    
            Integer integer = studentMapper.selectCount(studentQueryWrapper);
            System.out.println("有 " + integer + " 条数据");
        }
    }

![在这里插入图片描述][20200911165043414.png_pic_center]

### 1.3.5 分页 ###

**☞ 配置**

<bean id="sqlSessionFactory" class="com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"></property>
        
        <property name="configLocation" value="classpath:mybatis.xml"></property>
        
        <property name="plugins">
            <array>
                <bean class="com.baomidou.mybatisplus.extension.plugins.PaginationInterceptor">
                </bean>
            </array>
        </property>
    </bean>

**☞ 示例**

/** * Created with IntelliJ IDEA. * * @author Demo_Null * @date 2020/9/11 * @description 分页查询 */
    @SpringJUnitConfig(locations = "classpath:application.xml")
    public class Demo { 
    
        @Autowired
        private StudentMapper studentMapper;
    
        @Test
        public void TestPage() { 
            QueryWrapper<Student> studentQueryWrapper = new QueryWrapper<>();
    
            Page<Student> page = new Page<>();
            page.setSize(2);
            page.setCurrent(1);
    
            IPage<Student> selectPage = studentMapper.selectPage(page, studentQueryWrapper);
            System.out.println("总条数" + selectPage.getTotal());
            System.out.println("总页数" + selectPage.getPages());
            System.out.println("每页显示" + selectPage.getSize());
            System.out.println("当前页" + selectPage.getCurrent());
            System.out.println(selectPage.getRecords());
        }
    }

![在这里插入图片描述][20200911173422730.png_pic_center]

[20200911091956515.png_pic_center]: /images/20221123/c55db6725db14e1b8d533aea2dce54c6.png
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