两张表 xu_student 学生表，xu_major 专业表
下面是建表语句
CREATE TABLE `xu_student` (
`id` VARCHAR(20) NOT NULL COMMENT 'id',
`name` VARCHAR(55) DEFAULT NULL COMMENT '姓名',
`age` INT(11) DEFAULT NULL COMMENT '年龄',
`email` VARCHAR(55) DEFAULT NULL COMMENT '邮箱',
`m_id` INT(20) DEFAULT NULL COMMENT '班级',
PRIMARY KEY (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8`xu_student1`
CREATE TABLE `xu_major` (
`id` int(11) NOT NULL COMMENT '专业id',
`name` varchar(50) DEFAULT NULL COMMENT '专业名称',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
（数据自己填）
项目目录
Student.class 实体类
@Data //lombok简化代码，省去get，set方法
@TableName("xu_student")
public class Student implements Serializable {
@TableId
private String id;
private String name;
private Integer age;
private String email;
private Integer mId;
}
Major.class 实体类
@Data
@TableName("xu_major")
public class Major implements Serializable {
@TableId
private Integer Id;
private String name;
}
单表分页
首先要一个mybatis-plus的分页插件
MybatisPlusConfig.class
package com.mp.configuration;
import com.baomidou.mybatisplus.extension.plugins.PaginationInterceptor;
import com.baomidou.mybatisplus.extension.plugins.PerformanceInterceptor;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.transaction.annotation.EnableTransactionManagement;
/**
* mybatisPlus分页配置类
*/
@EnableTransactionManagement
@Configuration
@MapperScan("com.mp.dao")
public class MybatisPlusConfig {
/*
* 分页插件，自动识别数据库类型 多租户，请参考官网【插件扩展】
*/
@Bean
public PaginationInterceptor paginationInterceptor(){
return new PaginationInterceptor();
}
/**
* mybatis-plus SQL执行效率插件【生产环境可以关闭】
*/
@Bean
public PerformanceInterceptor performanceInterceptor() {
return new PerformanceInterceptor();
}
}
mybatis-plus自带的分页有两种方式：一种是返回list，一种是返回map
因为我写的是个接口所以我就按照我的代码分享了，知道哪些是核心就行
第一种：返回list
1，StudentService.java定义一个方法
List<Student> selectStudentPage(int current, int size);
2，StudentServiceImpl.java方法实现 (重点)
@Resource
private StudentMapper studentMapper;
/**
* 分页1
* @param current
* @param size
* @return *** list对象 ***
*/
@Override
public List<Student> selectStudentPage(int current, int size) {
QueryWrapper<Student> queryWrapper = new QueryWrapper<>();
// 判断年龄大于20岁的，这里用的是mybatis-plus的条件构造器
queryWrapper.gt("age",20);
/**
* 加上false就不查询总记录数啦,如果不需要的话可以加上false，这样就会少一条sql语句
* Page<Student> page = new Page<>(current,size,false);
*/
Page<Student> page = new Page<>(current,size);
// queryWrapper 可以为null 不进行条件判断
// 返回list 调用 selectPage
IPage<Student> userIPage = studentMapper.selectPage(page, queryWrapper);
System.out.println("总页数"+userIPage.getPages());
System.out.println("总记录数"+userIPage.getTotal());
//getRecords()分页对象记录列表
List<Student> records = userIPage.getRecords();
return records;
}
StudentController.java接口
@Autowired
private StudentService studentService;
/**
* 分页1 返回list 单表
* @param current 第几页
* @param size 每页数量
* @return list对象
*/
@GetMapping("/selectStudentPage/{current}/{size}")
public Object selectStudentPage(@PathVariable int current,@PathVariable int size){
List<Student> studentList = studentService.selectStudentPage(current, size);
return studentList;
}
第二种：返回map
1，StudentService.java定义一个方法
List<Map<String, Object>> selectStudentMapPage(int current, int size);
2，StudentServiceImpl.java方法实现 (重点)
/**
* 分页2
* @return *** map ***
*/
@Override
public List<Map<String, Object>> selectStudentMapPage(int current, int size) {
QueryWrapper<Student> wrapper = new QueryWrapper<>();
wrapper.gt("age",19);
Page<Student> page = new Page<>(current,size,false);
// 返回map调用 selectMapsPage
IPage<Map<String, Object>> mapIPage = studentMapper.selectMapsPage(page, wrapper);
System.out.println("总页数"+mapIPage.getPages());
System.out.println("总记录数"+mapIPage.getTotal());
List<Map<String, Object>> records = mapIPage.getRecords();
return records;
}
StudentController.java接口
@GetMapping("/selectStudentMapPage/{current}/{size}")
public Object selectStudentMapPage(@PathVariable int current,@PathVariable int size){
List<Map<String, Object>> maps = studentService.selectStudentMapPage(current, size);
return maps;
}
单表可以不用sql就可以进行分页，如果是多个表关联就需要来写sql语句啦
多表分页
在前面两个实体类的基础下，再添加一个实体类，为了保证实体类的属性和表结构一致，我们就再创建一个传输类，把我们要查的属性写进去。
StudentAndMajorVO .java
// 属性名和要映射的实体类保持一致
@Data
public class StudentAndMajorVO implements Serializable {
private String id;
private String name;
private Integer age;
private String email;
private String mname;
}
StudentMapper .xml
as mname 别名要和返回的StudentAndMajorVO中名字一样，不然会找不到，返回null
${ew.customSqlSegment} 是分页的方法
<select id="selectStudentAndMajorXmlPage" resultType="com.mp.entity.vo.StudentAndMajorVO">
SELECT s.*,m.`name` as mname
FROM xu_student s
LEFT JOIN xu_major m
ON s.m_id = m.id ${ew.customSqlSegment}
</select>
StudentMapper .java 在mapper接口中定义一个方法
package com.mp.dao;
import com.baomidou.mybatisplus.core.conditions.Wrapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.core.toolkit.Constants;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.mp.entity.Student;
import com.mp.entity.vo.StudentAndMajorVO;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import java.util.List;
@Mapper
public interface StudentMapper extends BaseMapper<Student>{
//@Param(Constants.WRAPPER) 固定写法
IPage<StudentAndMajorVO> selectStudentAndMajorXmlPage(Page<StudentAndMajorVO> page, @Param(Constants.WRAPPER) Wrapper<Student> wrapper);
}
StudentService.java
List<StudentAndMajorVO> selectStudentAndMajorXmlPage(int current, int size);
StudentServiceImpl.java
@Override
public List<StudentAndMajorVO> selectStudentAndMajorXmlPage(int current, int size) {
QueryWrapper<Student> wrapper = new QueryWrapper<>();
wrapper.gt("age",19);
Page<StudentAndMajorVO> page = new Page<>(current,size,false);
IPage<StudentAndMajorVO> studentAndMajorVOIPage = studentMapper.selectStudentAndMajorXmlPage(page, wrapper);
List<StudentAndMajorVO> records = studentAndMajorVOIPage.getRecords();
return records;
}
StudentController.java
@GetMapping("/selectStudentAndMajorXmlPage/{current}/{size}")
public Object selectStudentAndMajorXmlPage(@PathVariable int current,@PathVariable int size){
List<StudentAndMajorVO> studentAndMajorVOS = studentService.selectStudentAndMajorXmlPage(current, size);
return studentAndMajorVOS;
}
