【mybatis-plus】分页和联表查询

依赖

注意：如果引入了mybatis-plus就不要再引入mybatis-plus-boot-starter，而且mybatis-puls包是自己开发的，非官方的，建议引用mybatis-plus-boot-starter。注意spring和mysql包的版本关系。

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>2.3.0.RELEASE</version>
                <scope>import</scope>
                <type>pom</type>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.4.0</version>
        </dependency>
    </dependencies>

如果Mapper接口加了@Mapper注释，启动类不需要加@MapperScan

application.yml

server:
  port: 8081
spring:
  application:
    name: employ-manager
#mysql
  datasource:
    url: jdbc:mysql://localhost:3306/school?useUnicode=true&characterEncoding=utf8&serverTimezone = Asia/Shanghai
    username: root
    password: 123456


  #mybatis-plus
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  mapper-locations: classpath*:mybatis/*.xml
  type-aliases-package: com.jane.pojo

pojo

package com.jane.pojo;

import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.io.Serializable;

/**
 * @author jane
 * @date 2022/7/10
 */
@Data
@NoArgsConstructor
@AllArgsConstructor
@TableName("tbl_employee")
public class Employee implements Serializable {
    @TableField("id")
    private Integer id;
    @TableField("last_name")
    private String lastName;
    @TableField("email")
    private String email;
    @TableField("gender")
    private String gender;
    @TableField("age")
    private Integer age;
}

mapper

@Mapper
public interface EmployeeMapper extends BaseMapper<Employee> {
    List<Employee> selectByNameAndGender(String name,String gender);
}

为什么在测试时，注入的mapper为Null

需要引入@RunWith(SpringRunner.class)

@SpringBootTest
@RunWith(SpringRunner.class)
@Slf4j
public class EmployeeTest {
    @Resource
    private FilmMapper filmMapper;

    @Test
    public void test2(){
        List<Film> films = filmMapper.selectList(null);
        log.info("结果[{}]",films);
    }
}

分页

注意要mybatis-plus3.4.0版本才可以用新版的分页工具

config

@Configuration
public class MybatisPlusConfig {
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        // 添加分页插件
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }

}

page输入当前页和每页记录数

    @Test
    public void pageEmployTest(){
        Page<Employee> page = new Page<Employee>(1,5);
        Page<Employee> employeePage = employeeMapper.selectPage(page, null);
        log.info("分页结果：[{}]",employeePage.getRecords());
        log.info("当前页：{}，总页数：{}，记录数，{}",employeePage.getCurrent(),
        employeePage.getPages(),employeePage.getTotal());
    }

旧版本的拦截器：

@Bean
public PaginationInterceptor paginationInterceptor() {
    PaginationInterceptor paginationInterceptor = new PaginationInterceptor();
    // 设置请求的页面大于最大页后操作， true调回到首页，false 继续请求  默认false
    // paginationInterceptor.setOverflow(false);
    // 设置最大单页限制数量，默认 500 条，-1 不受限制
    // paginationInterceptor.setLimit(500);
    // 开启 count 的 join 优化,只针对部分 left join
    paginationInterceptor.setCountSqlParser(new JsqlParserCountOptimize(true));
    return paginationInterceptor;
}

性能分析插件

3.2.0版本以下可以用PerformanceInterceptor，以上的建议用第三方扩展插件 执行 SQL 分析打印

com.mysql.jdbc.Driver 是mybatis-connection-java 5 及 5 以下的
com.mysql.cj.jdbc.Driver是mybatis-connection-Java 6 及以上的

这里以第三方插件为例

依赖：

        <!--sql 分析打印-->
        <dependency>
            <groupId>p6spy</groupId>
            <artifactId>p6spy</artifactId>
            <version>3.8.2</version>
        </dependency>

application.yml修改

注意url处添加了p6spy和driver-class-name也是p6spy

#mysql
  datasource:
    url: jdbc:p6spy:mysql://localhost:3306/school?useUnicode=true&characterEncoding=utf8&serverTimezone = Asia/Shanghai
    username: root
    password: 123456
    driver-class-name: com.p6spy.engine.spy.P6SpyDriver

添加文件spy.properties

按自己需要修改driverlist

module.log=com.p6spy.engine.logging.P6LogFactory,com.p6spy.engine.outage.P6OutageFactory
# 自定义日志打印
logMessageFormat=com.baomidou.mybatisplus.extension.p6spy.P6SpyLogger


#日志输出到控制台，解开注释就行了
appender=com.baomidou.mybatisplus.extension.p6spy.StdoutLogger

# 指定输出文件位置
logfile=sql.log

# 使用日志系统记录 sql
#appender=com.p6spy.engine.spy.appender.Slf4JLogger
# 设置 p6spy driver 代理
deregisterdrivers=true
# 取消JDBC URL前缀
useprefix=true
# 配置记录 Log 例外,可去掉的结果集有error,info,batch,debug,statement,commit,rollback,result,resultset.
excludecategories=info,debug,result,batch,resultset
# 日期格式
dateformat=yyyy-MM-dd HH:mm:ss
# 实际驱动可多个
driverlist=com.mysql.cj.jdbc.Driver
# 是否开启慢SQL记录
outagedetection=true
# 慢SQL记录标准 2 秒
outagedetectioninterval=2

控制台会打印

Consume Time：19 ms 2022-07-10 10:56:41
Execute SQL：SELECT COUNT(1) FROM tbl_employee

联表查询

1、创建VO类，把两个表中你需要的字段提取出来

@Data
public class EmployeeVo {
    private String name;
    private String lastName;
}

2、在mapper中，用#{}作为条件，进行筛选

@Mapper
public interface EmployeeMapper extends BaseMapper<Employee> {
    @Select("select a.name,b.last_name\n" +
            "from film a,tbl_employee b where a.id=#{id} and a.id=b.id")
    List<EmployeeVo> list(Integer id);
}

常用条件：

eq:等于 =
ne:不等于 <>
gt:大于 >
ge:大于等于 >=
lt:小于 <
le:小于等于 <=
between:BETWEEN 值1 AND 值2
notBetween:NOT BETWEEN 值1 AND 值2
like:LIKE '%值%'
notLike:NOT LIKE '%值%'
likeLeft:LIKE '%值'
likeRight:LIKE '值%'
isNull:字段 IS NULL
isNotNull: 字段 IS NULL
in:字段 IN
notIn:字段 NOT IN
inSql:字段 IN ( sql语句 )
notInSql:字段 NOT IN ( sql语句 )
groupBy:分组：GROUP BY 字段, ...
orderByAsc:排序：ORDER BY 字段, ... ASC
orderByDesc 排序：ORDER BY 字段, ... DESC
orderBy:排序：ORDER BY 字段, ...
having:HAVING ( sql语句 )

.stream().forEach(x -> x.setColumn(StrUtil.toUnderlineCase(x.getColumn())));

list.forEach()

可以实现List的iterator()和Iterator的next()，这样就可以改变遍历的顺序了，而list.stream().forEach()则不行。list.stream().forEach()适用于非list

为了避免不必要的麻烦，在单纯只想迭代集合的场景下，应该直接使用forEach。

stream()是Collection接口的一个方法，但是Map接口并没有继承Collection，所以Map没有map.stream().forEach()

BeanUtil.copyProperties(a, assetVo);复制类

【mybatis-plus】分页和联表查询

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