mybatis-plus详细使用教程

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mybatis-plus使用教程

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什么是Mybatis-Plus

MyBatis-Plus (opens new window)(简称 MP)是一个 MyBatis (opens new window)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。

  • 无侵入:只做增强不做改变,引入它不会对现有工程产生影响,如丝般顺滑
  • 损耗小:启动即会自动注入基本 CURD,性能基本无损耗,直接面向对象操作
  • 强大的 CRUD 操作:内置通用 Mapper、通用 Service,仅仅通过少量配置即可实现单表大部分 CRUD 操作,更有强大的条件构造器,满足各类使用需求
  • 支持 Lambda 形式调用:通过 Lambda 表达式,方便的编写各类查询条件,无需再担心字段写错
  • 支持主键自动生成:支持多达 4 种主键策略(内含分布式唯一 ID 生成器 - Sequence),可自由配置,完美解决主键问题
  • 支持 ActiveRecord 模式:支持 ActiveRecord 形式调用,实体类只需继承 Model 类即可进行强大的 CRUD 操作
  • 支持自定义全局通用操作:支持全局通用方法注入( Write once, use anywhere )
  • 内置代码生成器:采用代码或者 Maven 插件可快速生成 Mapper 、 Model 、 Service 、 Controller 层代码,支持模板引擎,更有超多自定义配置等您来使用
  • 内置分页插件:基于 MyBatis 物理分页,开发者无需关心具体操作,配置好插件之后,写分页等同于普通 List 查询
  • 分页插件支持多种数据库:支持 mysql、MariaDB、Oracle、DB2、H2、HSQL、SQLite、Postgre、SQLServer 等多种数据库
  • 内置性能分析插件:可输出 SQL 语句以及其执行时间,建议开发测试时启用该功能,能快速揪出慢查询
  • 内置全局拦截插件:提供全表 delete 、 update 操作智能分析阻断,也可自定义拦截规则,预防误操作

快速入门

1、创建数据库和数据库表

(来自官网的例子)

DROP TABLE IF EXISTS user;

CREATE TABLE user
(
    id BIGINT(20) NOT NULL COMMENT \'主键ID\',
    name VARCHAR(30) NULL DEFAULT NULL COMMENT \'姓名\',
    age INT(11) NULL DEFAULT NULL COMMENT \'年龄\',
    email VARCHAR(50) NULL DEFAULT NULL COMMENT \'邮箱\',
    PRIMARY KEY (id)
);

2、插入表数据

DELETE FROM user;

INSERT INTO user (id, name, age, email) VALUES
(1, \'Jone\', 18, \'test1@baomidou.com\'),
(2, \'Jack\', 20, \'test2@baomidou.com\'),
(3, \'Tom\', 28, \'test3@baomidou.com\'),
(4, \'Sandy\', 21, \'test4@baomidou.com\'),
(5, \'Billie\', 24, \'test5@baomidou.com\');

3、新建springboot工程,引入mubatis-plus依赖

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.1.0</version>
</dependency>

4、application.yml配置mysql数据源

# DataSource Config
spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost/mp_plus?serverTimezone=GMT%2B8&characterEncoding=UTF-8&allowMultiQueries=true
    username: root
    password: 123456

5、使用mybatis-plus

  • entity

    @Data
    @AllArgsConstructor
    @NoArgsConstructor
    public class User {
      @TableId(type = IdType.AUTO) //采用数据库自增
      private long id;
      private String name;
      private int age;
      private String email;
    }
  • mapper接口
// 在对应的Mapper上面继承基本的类 BaseMapper
@Repository
public interface UserMapper extends BaseMapper<User> {
    // 所有的CRUD操作都已经编写完成了
}
  • springboot测试启动类增加@MapperScan扫描注解

    @MapperScan("com.mpstudy.mp.mapper")
  • 测试
@MapperScan("com.mpstudy.mp.mapper")
@SpringBootTest
class MpApplicationTests {

    // 继承了BaseMapper,所有的方法都来自己父类
    // 我们也可以编写自己的扩展方法!
    @Autowired
    UserMapper userMapper;

    @Test
    void contextLoads() {
        List<User> users = userMapper.selectList(null); //条件构造器先不用
        users.forEach(System.out::println);
    }
}
  • 测试结果
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@75023c53]
User(id=1, name=Jone, age=18, email=test1@baomidou.com, createTime=null, updateTime=null)
User(id=2, name=Jack, age=20, email=test2@baomidou.com, createTime=null, updateTime=null)
User(id=3, name=Tom, age=28, email=test3@baomidou.com, createTime=null, updateTime=null)
User(id=4, name=Sandy, age=21, email=test4@baomidou.com, createTime=null, updateTime=null)
User(id=5, name=Billie, age=24, email=test5@baomidou.com, createTime=null, updateTime=null)

日志配置

1、在application.yml中新增配置

mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl //标准输出

2、日志配置完成后,在控制台就会生成相应的日志

Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@75023c53] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@688197093 wrapping com.mysql.jdbc.JDBC4Connection@3610f277] will not be managed by Spring
==>  Preparing: SELECT id,name,age,email,create_time,update_time FROM user 
==> Parameters: 
<==    Columns: id, name, age, email, create_time, update_time
<==        Row: 1, Jone, 18, test1@baomidou.com, null, null
<==        Row: 2, Jack, 20, test2@baomidou.com, null, null
<==        Row: 3, Tom, 28, test3@baomidou.com, null, null
<==        Row: 4, Sandy, 21, test4@baomidou.com, null, null
<==        Row: 5, Billie, 24, test5@baomidou.com, null, null

CRUD详解

1、插入操作

@Test
void insert(){
    User user = new User();
    user.setName("java大师1");
    user.setAge(11);
    user.setEmail("111000@qq.com");
    int insert = userMapper.insert(user);
}

上面的的例子中没有插入用户id,在User类中已经设置了自动,也就是跟着数据库的配置走(数据库中已经设置了自增)

2、更新操作

@Test
void update(){
    User user = new User();
    user.setId(6);
    user.setAge(38);
    int i = userMapper.updateById(user); //传入的是个对象
    System.out.println(i);
}

3、时间戳自动填充

实现方法有如下两种:

  • 编写时间戳自动填充注解

    import com.baomidou.mybatisplus.core.handlers.MetaObjectHandler;
    import lombok.extern.slf4j.Slf4j;
    import org.apache.ibatis.reflection.MetaObject;
    import org.springframework.stereotype.Component;
    
    import java.util.Date;
    
    @Slf4j
    @Component
    public class MyMetaObjectHandler implements MetaObjectHandler {
      @Override
      public void insertFill(MetaObject metaObject) {
          log.info("开始填充");
          this.setFieldValByName("createTime",new Date(),metaObject);
          this.setFieldValByName("updateTime",new Date(),metaObject);
      }
    
      @Override
      public void updateFill(MetaObject metaObject) {
          log.info("更新填充");
          this.setFieldValByName("updateTime",new Date(),metaObject);
      }
    }
  • 在实体类的字段上增加TableField注解

    @Data
    @AllArgsConstructor
    @NoArgsConstructor
    public class User {
    
      @TableId(type = IdType.AUTO)
      private long id;
      private String name;
      private int age;
      private String email;
    
      //创建时间注解
      @TableField(fill = FieldFill.INSERT)
      private Date createTime;
    //修改时间注解
      @TableField(fill = FieldFill.INSERT_UPDATE)
      private Date updateTime;
    }
  • 测试

    @Test
    void insert(){
      User user = new User();
      user.setName("公众号:java大师");
      user.setAge(2);
      user.setEmail("javadashi@qq.com");
      int insert = userMapper.insert(user);
    }

4、删除操作

// 测试删除
@Test
public void testDeleteById(){
    userMapper.deleteById(1);
} 

// 通过id批量删除
@Test
public void testDeleteBatchId(){
    userMapper.deleteBatchIds(Arrays.asList(2,3,4));
} 

// 通过map删除
@Test
public void testDeleteMap(){
HashMap<String, Object> map = new HashMap<>();
map.put("name","java大师");
userMapper.deleteByMap(map);

5、逻辑删除

相对于物理删除来说,我们需要对数据进行留档,所以需要对删除的数据也要保留,这就要用到逻辑删除

  • 在数据库表中增加sfyx(是否有效)字段

  • 实体类增加属性

    @TableLogic //逻辑删除
    private Integer sfyx;
  • 配置逻辑删除组件并被springboot所管理

    // 逻辑删除组件!
    @Bean
    public ISqlInjector sqlInjector() {
    return new LogicSqlInjector();
    }
  • 修改application.yml增加配置

    mybatis-plus:
    configuration:
      log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
    global-config:
      db-config:
        logic-delete-value: 0  //已删除
        logic-not-delete-value: 1  //未删除
  • 测试(看到虽然执行的的delete方法,但是实际的sql是update语句)

    @Test
      void testDelete(){
          int i = userMapper.deleteById(2);
      }
    Creating a new SqlSession
    SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@456bcb74] was not registered for synchronization because synchronization is not active
    JDBC Connection [HikariProxyConnection@66747889 wrapping com.mysql.jdbc.JDBC4Connection@4dd90166] will not be managed by Spring
    ==>  Preparing: UPDATE user SET sfyx=0 WHERE id=? AND sfyx=1 
    ==> Parameters: 2(Integer)
    <==    Updates: 1

6、分页查询

  • 配置分页拦截器

    @Bean
    public PaginationInterceptor paginationInterceptor(){
      return new PaginationInterceptor();
    }
  • 使用Page对象

    @Test
    void testPage(){
      Page<User> page = new Page<>(1,3);
      userMapper.selectPage(page, null);
      page.getRecords().forEach(System.out::println);
      System.out.println(page.getTotal());
    }

7、多表查询

  • 创建VO对象

    import com.mpstudy.mp.entity.User;
    import lombok.Data;
    
    @Data
    public class UserClassVo extends User {
      private String className;
    }
  • UserMapper中增加getAllUsers方法,通过select注解编写sql
@Repository
public interface UserMapper extends BaseMapper<User> {
    @Select("select a.*,b.name as class_name from user a,class b,user_class c where a.id=c.user_id and b.id=c.class_id ")
    List<UserClassVo> getAllUsers();
}
  • 测试

    @Test
    void testGetAllUsers(){
      List<UserClassVo> allUsers = userMapper.getAllUsers();
      allUsers.forEach(System.out::println);
    }
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@47f04e4d] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@843410864 wrapping com.mysql.jdbc.JDBC4Connection@5f5827d0] will not be managed by Spring
==>  Preparing: select a.*,b.name as class_name from user a,class b,user_class c where a.id=c.user_id and b.id=c.class_id 
==> Parameters: 
<==    Columns: id, name, age, email, create_time, update_time, sfyx, class_name
<==        Row: 2, Jack, 20, test2@baomidou.com, null, 2021-09-20 18:05:06.0, 0, 小二班
<==        Row: 3, Tom, 28, test3@baomidou.com, null, 2021-09-20 18:04:27.0, 1, 大一班

8、多表分页查询

  • 创建VO对象

    import com.mpstudy.mp.entity.User;
    import lombok.Data;
    
    @Data
    public class UserClassVo extends User {
      private String className;
    }
  • UserMapper中增加getUsersByPage方法,通过select注解编写sql

    @Repository
    public interface UserMapper extends BaseMapper<User> {
      //传入IPage对象和QueryWrapper条件构造器
      //sql通过${ew.customSqlSegment}去解析构造器内容
      @Select("select a.*,c.name as class_name from user a left join user_class b on a.id=b.user_id left join class c on b.class_id = c.id " + "${ew.customSqlSegment} ")
      IPage<UserClassVo> getUsersByPage(IPage<UserClassVo> page,@Param(Constants.WRAPPER) QueryWrapper wrapper);
    }
  • 测试

    @Test
    void testGetUsersByPage(){
      Page<UserClassVo> page = new Page<>(2,2);
      QueryWrapper<UserClassVo> wrapper = new QueryWrapper<>();
      wrapper.likeRight("a.name","java");
      userMapper.getUsersByPage(page,wrapper);
      page.getRecords().forEach(System.out::println);
    }
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@f438904] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@766089249 wrapping com.mysql.jdbc.JDBC4Connection@62cba181] will not be managed by Spring
 JsqlParserCountOptimize sql=select a.*,c.name as class_name from user a left join user_class b on a.id=b.user_id left join class c on b.class_id = c.id WHERE a.name LIKE ?
==>  Preparing: SELECT COUNT(1) FROM user a LEFT JOIN user_class b ON a.id = b.user_id LEFT JOIN class c ON b.class_id = c.id WHERE a.name LIKE ? 
==> Parameters: java%(String)
<==    Columns: COUNT(1)
<==        Row: 3
==>  Preparing: select a.*,c.name as class_name from user a left join user_class b on a.id=b.user_id left join class c on b.class_id = c.id WHERE a.name LIKE ? LIMIT ?,? 
==> Parameters: java%(String), 0(Long), 2(Long)
<==    Columns: id, name, age, email, create_time, update_time, sfyx, class_name
<==        Row: 6, java大师, 38, javadashi@qq.com, null, 2021-09-20 18:04:29.0, 1, 小二班
<==        Row: 7, java大师, 11, javadashi@qq.com, null, 2021-09-20 18:04:29.0, 1, 大一班
<==      Total: 2

10、条件构造器

支持:allEq,eq,isNull等等,具体见:条件构造器 | MyBatis-Plus (baomidou.com)

  • 测试
@Test
void testWrapper01(){
    // 查询name不为空的用户,并且邮箱不为空的用户,年龄大于等于12记录
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.isNotNull("name").isNotNull("create_time").gt("age",12);
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
}

@Test
void testWrapper02(){
    // 查询年龄18到24之间的记录
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.between("age",18,24);
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
}

@Test
void testWrapper03(){
    // 名字中带java的记录
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.likeRight("name","java");
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
}

11、性能分析插件

  • 导入插件

    @Bean
    @Profile({"dev"}) //开发环境运行
    public PerformanceInterceptor performanceInterceptor(){
      PerformanceInterceptor interceptor = new PerformanceInterceptor();
      interceptor.setFormat(true); //格式化sql
      interceptor.setMaxTime(20);  //设置超时时长,单位毫秒
      return interceptor;
    }
  • application.xml设置为dev开发模式

    # DataSource Config
    spring:
    profiles:
      active: dev
  • 测试(日志最后1行显示超时报错)

    org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.exceptions.PersistenceException: 
    ### Error querying database.  Cause: com.baomidou.mybatisplus.core.exceptions.MybatisPlusException:  The SQL execution time is too large, please optimize ! 
    ### The error may exist in com/mpstudy/mp/mapper/UserMapper.java (best guess)
    ### The error may involve com.mpstudy.mp.mapper.UserMapper.getUsersByPage
    ### The error occurred while handling results
    ### SQL: select a.*,c.name as class_name from user a left join user_class b on a.id=b.user_id left join class c on b.class_id = c.id WHERE a.name LIKE ? LIMIT ?,?
    ### Cause: com.baomidou.mybatisplus.core.exceptions.MybatisPlusException:  The SQL execution time is too large, please optimize ! 

12、代码自动生成器

  • 导入依赖

    <dependency>
      <groupId>com.baomidou</groupId>
      <artifactId>mybatis-plus-generator</artifactId>
      <version>3.1.0</version>
    </dependency>
  • 代码生成

    import com.baomidou.mybatisplus.annotation.DbType;
    import com.baomidou.mybatisplus.annotation.FieldFill;
    import com.baomidou.mybatisplus.annotation.IdType;
    import com.baomidou.mybatisplus.generator.AutoGenerator;
    import com.baomidou.mybatisplus.generator.InjectionConfig;
    import com.baomidou.mybatisplus.generator.config.DataSourceConfig;
    import com.baomidou.mybatisplus.generator.config.GlobalConfig;
    import com.baomidou.mybatisplus.generator.config.PackageConfig;
    import com.baomidou.mybatisplus.generator.config.StrategyConfig;
    import com.baomidou.mybatisplus.generator.config.po.TableFill;
    import com.baomidou.mybatisplus.generator.config.rules.DateType;
    import com.baomidou.mybatisplus.generator.config.rules.NamingStrategy;
    
    import java.util.ArrayList;
    import java.util.HashMap;
    import java.util.Map;
    
    //代码自动生成器
    public class CodeGenerator {
    
      public static void main(String[] args) {
          //构建一个 代码自动生成器 对象
          AutoGenerator autoGenerator = new AutoGenerator();
    
          //1、全局配置
          GlobalConfig gc = new GlobalConfig();
          String oPath = System.getProperty("user.dir");//得到当前项目的路径
          gc.setOutputDir(oPath + "/src/main/java");   //生成文件输出根目录
          gc.setOpen(false);//生成完成后不弹出文件框
          gc.setFileOverride(true);  //文件覆盖
          gc.setAuthor("ryan");// 作者
          gc.setServiceName("%sService");    //去除Service的I前綴
          gc.setIdType(IdType.ID_WORKER);
          gc.setDateType(DateType.ONLY_DATE);
          gc.setSwagger2(true);
          autoGenerator.setGlobalConfig(gc);
    
          ///2、数据源配置
          DataSourceConfig dsc = new DataSourceConfig();
          dsc.setDbType(DbType.MYSQL);   //设置数据库类型
          dsc.setUrl("jdbc:mysql://localhost:3306/mp_plus?useSSL=false&useUnicode=true&characterEncoding=utf-8&serverTimezone=GMT%2B8");  //指定数据库
          dsc.setDriverName("com.mysql.jdbc.Driver");
          dsc.setUsername("root");
          dsc.setPassword("root");
          autoGenerator.setDataSource(dsc);
    
          //3、包的配置
          PackageConfig pc = new PackageConfig();
          pc.setModuleName("mp");
          pc.setParent("com.mpstudy");
          pc.setEntity("pojo");
          pc.setMapper("mapper");
          pc.setService("service");
          pc.setController("controller");
          autoGenerator.setPackageInfo(pc);
    
          // 4、策略配置
          StrategyConfig strategy = new StrategyConfig();
          strategy.setInclude("user","user_class","class"); // 设置要映射的表名
          strategy.setNaming(NamingStrategy.underline_to_camel);
          strategy.setColumnNaming(NamingStrategy.underline_to_camel);
          strategy.setEntityLombokModel(true); // 自动lombok;
          strategy.setLogicDeleteFieldName("deleted");
          strategy.setTablePrefix("tb_"); //去掉表的前缀
          // 自动填充配置
          TableFill gmtCreate = new TableFill("create_time", FieldFill.INSERT);
          TableFill gmtModified = new TableFill("update_time", FieldFill.INSERT_UPDATE);
          ArrayList<TableFill> tableFills = new ArrayList<>();
          tableFills.add(gmtCreate);
          tableFills.add(gmtModified);
          strategy.setTableFillList(tableFills);
          // 乐观锁
          strategy.setVersionFieldName("version");strategy.setRestControllerStyle(true);
          strategy.setControllerMappingHyphenStyle(true);
          autoGenerator.setStrategy(strategy);
    
          //不加这个会报空指针异常
          InjectionConfig injectionConfig = new InjectionConfig() {
              //自定义属性注入:abc
              //在.ftl(或者是.vm)模板中,通过${cfg.abc}获取属性
              @Override
              public void initMap() {
                  Map<String, Object> map = new HashMap<>();
                  map.put("abc", this.getConfig().getGlobalConfig().getAuthor() + "-mp");
                  this.setMap(map);
              }
          };
          //自定义配置
          autoGenerator.setCfg(injectionConfig);
    
          // 执行生成
          autoGenerator.execute();
      }
    }
    

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