mybatis-plus详细使用教程

Posted 2021-09-22 老方学IT

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, \'[e-mail]\'),
(2, \'Jack\', 20, \'[e-mail]\'),
(3, \'Tom\', 28, \'[e-mail]\'),
(4, \'Sandy\', 21, \'[e-mail]\'),
(5, \'Billie\', 24, \'[e-mail]\');

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=[e-mail], createTime=null, updateTime=null)
User(id=2, name=Jack, age=20, email=[e-mail], createTime=null, updateTime=null)
User(id=3, name=Tom, age=28, email=[e-mail], createTime=null, updateTime=null)
User(id=4, name=Sandy, age=21, email=[e-mail], createTime=null, updateTime=null)
User(id=5, name=Billie, age=24, email=[e-mail], 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, [e-mail], null, null
<==        Row: 2, Jack, 20, [e-mail], null, null
<==        Row: 3, Tom, 28, [e-mail], null, null
<==        Row: 4, Sandy, 21, [e-mail], null, null
<==        Row: 5, Billie, 24, [e-mail], 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("[e-mail]");
    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("[e-mail]");
    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, [e-mail], null, 2021-09-20 18:05:06.0, 0, 小二班
<==        Row: 3, Tom, 28, [e-mail], 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, [e-mail], null, 2021-09-20 18:04:29.0, 1, 小二班
<==        Row: 7, java大师, 11, [e-mail], 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();
    }
  }