Mybatis-plus入门教程

环境搭建

SpringBoot+Mybatis-Plus

1. 引入pom依赖

<?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">
    <parent>
        <artifactId>lagou-study</artifactId>
        <groupId>com.mmc</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>mybatis-plus</artifactId>


    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
            <version>2.1.2.RELEASE</version>
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-logging</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <version>2.1.2.RELEASE</version>
            <scope>test</scope>
        </dependency>

        <!--简化代码的⼯具包-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.22</version>
        </dependency>
        <!--mybatis-plus的springboot⽀持-->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.1.1</version>
        </dependency>
        <!--mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.13</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>2.0.0-alpha0</version>
        </dependency>


    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>2.1.2.RELEASE</version>
            </plugin>
        </plugins>
    </build>
</project>

2. application.properties文件

spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=utf8&autoReconnect=true&allowMultiQueries=true&useSSL=false&serverTimezone=UTC
spring.datasource.username=root
spring.datasource.password=0490218292

3. log4j.properties

log4j.rootLogger=DEBUG,A1
log4j.appender.A1=org.apache.log4j.ConsoleAppender
log4j.appender.A1.layout=org.apache.log4j.PatternLayout
log4j.appender.A1.layout.ConversionPattern=[%t] [%c]-[%p] %m%n

4. 编写实体类

@Data
@AllArgsConstructor
@NoArgsConstructor
@TableName("user")
public class User {

    private Integer id;

    private String name;
}

5. 编写Mapper

public interface UserMapper extends BaseMapper<User> {
}

6. 测试

@SpringBootTest
@RunWith(SpringRunner.class)
public class UserMapperTest {

    @Autowired
    private UserMapper userMapper;


    @Test
    public void testSelect(){
        List<User> users = userMapper.selectList(null);
        System.out.println(users);
    }
}

基本使用

下面会根据如下要点讲解mybatis-plus的基本功能

• 实体类注解
• 分页
• 基本配置
• 性能分析插件、乐观锁等插件
• 自动填充属性值
• SQL注入器
• 逻辑删除
• MybatisX插件

实体类注解

@Data
@AllArgsConstructor
@NoArgsConstructor
@TableName("user")
public class User {

    //id类型子增长
    @TableId(type = IdType.AUTO)
    private Integer id;

    @TableField(value = "name")
    private String userName;

    private Integer age;

    //不查询该字段
    @TableField(select = false)
    private Date createTime;
}

分页插件

配置：

@Configuration
@MapperScan("com.mmc.mybatisPlus.mapper") //设置mapper接⼝的扫描包
public class MybatisPlusConfig {
/**
* 分⻚插件
*/
@Bean
public PaginationInterceptor paginationInterceptor() {
    return new PaginationInterceptor();
}
}

测试代码：

 @Test
    public void testPage(){
        Page<User> page=new Page<>(1,3);
        IPage<User> userIPage = userMapper.selectPage(page,null);
        System.err.println(userIPage.getRecords());
    }

基本配置

#指定配置文件位置
mybatis-plus.config-location = classpath:mybatis-config.xml
#指定mapper的文件位置
mybatis-plus.mapper-locations = classpath*:mybatis/*.xml
#指定别名包扫描路径，配置后可直接使用类名，而不用全类名
mybatis-plus.type-aliases-package = com.mmc.mybatisPlus.bean
#关闭⾃动驼峰映射，该参数不能和mybatis-plus.config-location同时存在
mybatis-plus.configuration.map-underscore-to-camel-case=false
#全局地开启或关闭配置⽂件中的所有映射器已经配置的任何缓存，默认为 true。
mybatis-plus.configuration.cache-enabled=false

#全局配置表名前缀
mybatis-plus.global-config.db-config.table-prefix=tb_

插件使用

1. 基础使用

@Component
@Intercepts({
        @Signature(
                type= Executor.class,
                method = "query",
                args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}
        )})
public class MyInterceptor implements Interceptor {

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        System.out.println("拦截excecutor");
        //拦截方法，具体业务逻辑编写的位置
        return invocation.proceed();
    }

    @Override
    public Object plugin(Object o) {
        //创建target对象的代理对象,⽬的是将当前拦截器加⼊到该对象中
        return Plugin.wrap(o,this);
    }

    @Override
    public void setProperties(Properties properties) {

    }
}

2. 性能分析插件

用于输出每条SQL语句及其执行时间，可以设置最大执行时间，超过时间会抛出异常。

 @Bean
    public PerformanceInterceptor performanceInterceptor(){
        PerformanceInterceptor performanceInterceptor = new
                PerformanceInterceptor();
        performanceInterceptor.setMaxTime(100);
        performanceInterceptor.setFormat(true);
        return performanceInterceptor;
    }

3. 乐观锁插件

@Bean
public OptimisticLockerInterceptor optimisticLockerInterceptor() {
return new OptimisticLockerInterceptor();
}

实体类上加上@version注解

@Version
private Integer version;

自动填充功能

1. 给要填充的字段加注解

   @TableField(fill = FieldFill.INSERT)
    private Date createTime;

填充策略有多种：

public enum FieldFill {

/**
* 默认不处理
*/
DEFAULT,
/**
* 插⼊时填充字段
*/
INSERT,
/**
* 更新时填充字段
*/
UPDATE,
/**
* 插⼊和更新时填充字段
*/
INSERT_UPDATE

    
}

编写MyMetaObjectHandler

@Component
public class MyMetaObjectHandler implements MetaObjectHandler {

    @Override
    public void insertFill(MetaObject metaObject) {
        Object createTime = getFieldValByName("createTime", metaObject);
        if(createTime==null){
            setFieldValByName("createTime",new Date(),metaObject);
        }
    }

    @Override
    public void updateFill(MetaObject metaObject) {

    }
}

SQL注入器

在Mytabis-Plus中，通过AbstractSqlInjector将BaseMapper中的方法注入到Mybatis容器中，这样它的方法才能被正常执行。那么我们如果需要扩展BaseMapper中的方法，该怎么实现呢？

1. 编写一个MybaseMapper继承BaseMapper

public interface MyBaseMapper<T> extends BaseMapper<T> {
List<T> findAll();
}

2. 给对应的要扩展的方法编写方法类

public class FindAll extends AbstractMethod {

    @Override
    public MappedStatement injectMappedStatement(Class<?> mapperClass, Class<?> modelClass, TableInfo tableInfo) {
        String sqlMethod="findAll";
        String sql="select * from "+tableInfo.getTableName();
        SqlSource sqlSource = languageDriver.createSqlSource(configuration, sql, modelClass);
        return this.addSelectMappedStatement(mapperClass,sqlMethod,sqlSource,modelClass,tableInfo);
    }
}

3. 注入到容器

@Component
public class MySqlInjector extends DefaultSqlInjector {

    @Override
    public List<AbstractMethod> getMethodList() {
        List<AbstractMethod> methodList = super.getMethodList();
        methodList.add(new FindAll());

        return methodList;
    }
}

逻辑删除

1. 实体类加注解

@TableLogic
    private Integer deleted;

2. 配置删除属性值

# 逻辑已删除值(默认为 1)
mybatis-plus.global-config.db-config.logic-delete-value=1
# 逻辑未删除值(默认为 0)
mybatis-plus.global-config.db-config.logic-not-delete-value=0