mybatis-plus分页插件使用

1.准备工作

mybatis-plus分页插件需要先进行配置

@Configuration
public class MyBatisPlusConfig {
    /**
     *  mybatis-plus分页插件
     */
    @Bean
    public PaginationInterceptor paginationInterceptor() {
        PaginationInterceptor paginationInterceptor = new PaginationInterceptor();
        return paginationInterceptor;
    }
}

根据版本不同,配置方式可能稍有不同,分页的原理就是通过ibatis提供的sql拦截器进行sql拼接,如果不配置分页将失效,变成普通的列表查询

如果系统中有多个分页插件例如 pagehelper 等,如果未使用自动配置,或冲突的话,也需要进行手动配置

2.使用

测试使用到的类和数据库定义如下

学生信息类

@Data
@TableName("student")
public class Student {

    @TableId(type = IdType.AUTO)
    private Integer id;

    private String name;

    private Integer age;

    private Integer sex;

    private Integer classId;
}

班级信息类

@Data
@TableName("class")
public class Class {

    @TableId(type = IdType.AUTO)
    private Integer id;

    private String name;

    private Integer grade;

    private Integer classIndex;
}

数据库定义

create table student
(
    id       int auto_increment
        primary key,
    name     varchar(255) null,
    age      int          null,
    sex      int(1)       null,
    class_id int          null
);
create table class
(
    id          int auto_increment
        primary key,
    name        varchar(255) null,
    grade       int          null,
    class_index int          null
);

• 基础使用,使用BaseMapper 提供的分页方法

  Page<Student> studentPage = new Page<Student>(1L, 2L);
  Page<Student> studentPage1 = studentMapper.selectPage(studentPage, null);

  studentPage 和 studentPage1 是完全相同的对象,在Page<T> 类中就保存有分页和查询结果,selectPage方法定义如下

  /**
       * 根据 entity 条件，查询全部记录（并翻页）
       *
       * @param page         分页查询条件（可以为 RowBounds.DEFAULT）
       * @param queryWrapper 实体对象封装操作类（可以为 null）
       */
      <E extends IPage<T>> E selectPage(E page, @Param(Constants.WRAPPER) Wrapper<T> queryWrapper);

  可以通过 queryWrapper拼接自定义参数

  
• 对于一些复杂查询,连表或者自定义xml等使用 
  mapper接口定义

Page<StudentVO> selectStudentInfoPage(Page<StudentVO> studentVOPage, @Param("sex") Integer sex);

自定义xml如下

    <select id="selectStudentInfoPage" resultType="com.school.beans.vo.StudentVO">
        select s.id as id,
               s.name as name,
               s.age as age,
               s.sex as sex,
               s.class_id as classId,
               c.name as className,
               c.grade as grade,
               c.class_index as classIndex
        from student s join class c on s.class_id = c.id
        <where>
            <if test="sex != null">
                s.sex = #{sex}
            </if>
        </where>
    </select>

调用

Page<StudentVO> studentVOPage = new Page<>(1L, 2L);
        Page<StudentVO> studentVOPage1 = studentMapper.selectStudentInfoPage(studentVOPage, 0);

结果

打印sql

==>  Preparing: SELECT COUNT(1) FROM student s JOIN class c ON s.class_id = c.id WHERE s.sex = ? 
==> Parameters: 0(Integer)
<==    Columns: COUNT(1)
<==        Row: 4
==>  Preparing: select s.id as id, s.name as name, s.age as age, s.sex as sex, s.class_id as classId, c.name as className, c.grade as grade, c.class_index as classIndex from student s join class c on s.class_id = c.id WHERE s.sex = ? LIMIT ?,? 
==> Parameters: 0(Integer), 0(Long), 2(Long)
<==    Columns: id, name, age, sex, classId, className, grade, classIndex
<==        Row: 1, 喵帕斯, 5, 0, 1, 一年级一班, 1, 1
<==        Row: 2, 一条萤, 8, 0, 4, 二年级二班, 2, 2
<==      Total: 2
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@5cbe95b1]

 

这种方式需要手动多传入一个page参数,如果自定义参数较多的情况下可能会比较麻烦.其实mybatis

• 使用一个参数进行分页

mapper定义

Page<StudentVO> selectStudentInfoPage2(StudentPageDTO studentPageDTO);

xml与上一种方法类似,只是这里只传入一个参数

 

<select id="selectStudentInfoPage2" resultType="com.school.beans.vo.StudentVO">
        select s.id as id,
        s.name as name,
        s.age as age,
        s.sex as sex,
        s.class_id as classId,
        c.name as className,
        c.grade as grade,
        c.class_index as classIndex
        from student s join class c on s.class_id = c.id
        <where>
            <if test="sex != null">
                s.sex = #{sex}
            </if>
        </where>
    </select>

调用方法

StudentPageDTO studentPageDTO = new StudentPageDTO(0);
        Page<StudentVO> studentVOPage2 = studentMapper.selectStudentInfoPage2(studentPageDTO);

打印sql

==>  Preparing: SELECT COUNT(1) FROM student s JOIN class c ON s.class_id = c.id WHERE s.sex = ? 
==> Parameters: 0(Integer)
<==    Columns: COUNT(1)
<==        Row: 4
==>  Preparing: select s.id as id, s.name as name, s.age as age, s.sex as sex, s.class_id as classId, c.name as className, c.grade as grade, c.class_index as classIndex from student s join class c on s.class_id = c.id WHERE s.sex = ? LIMIT ?,? 
==> Parameters: 0(Integer), 0(Long), 10(Long)
<==    Columns: id, name, age, sex, classId, className, grade, classIndex
<==        Row: 1, 喵帕斯, 5, 0, 1, 一年级一班, 1, 1
<==        Row: 2, 一条萤, 8, 0, 4, 二年级二班, 2, 2
<==        Row: 3, 夏海, 9, 0, 5, 二年级三班, 2, 3
<==        Row: 4, 鞠, 10, 0, 10, 五年级一班, 5, 1
<==      Total: 4
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@118fbaf0]

结果

 

 可以看到参数和返回结果是同一对象,可以使用该方式进行分页的原因很简单,参数DTO继承了分页对象

@Data
@AllArgsConstructor
public class StudentPageDTO extends Page {
    private Integer sex;
}

本质上和第一种分页没有区别

总结三种分页本质上都是一样的,通过拦截器拦截分页参数,拼接参数

总结下本人知道的三种方式:

1. 使用mp自带的分页方法分页,优点是方便,缺点是不可以自定义xml对于复杂查询不是很友好

2.自定义xml,传入多个参数,其中包括一个page对象作为分页参数

3.自定义参数DTO继承page对象,传入该对象也可以作为分页参数

3可以看成对于2的一种改造,具体使用看取舍