mybatis-plus分頁插件使用

1.准備工作

mybatis-plus分頁插件需要先進行配置

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

根據版本不同,配置方式可能稍有不同,分頁的原理就是通過ibatis提供的sql攔截器進行sql拼接,如果不配置分頁將失效,變成普通的列表查詢

如果系統中有多個分頁插件例如 pagehelper 等,如果未使用自動配置,或沖突的話,也需要進行手動配置

2.使用

測試使用到的類和數據庫定義如下

學生信息類

@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;
}

班級信息類

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

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

    private String name;

    private Integer grade;

    private Integer classIndex;
}

數據庫定義

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
);

• 基礎使用,使用BaseMapper 提供的分頁方法

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

  studentPage 和 studentPage1 是完全相同的對象,在Page<T> 類中就保存有分頁和查詢結果,selectPage方法定義如下

  /**
       * 根據 entity 條件，查詢全部記錄（並翻頁）
       *
       * @param page         分頁查詢條件（可以為 RowBounds.DEFAULT）
       * @param queryWrapper 實體對象封裝操作類（可以為 null）
       */
      <E extends IPage<T>> E selectPage(E page, @Param(Constants.WRAPPER) Wrapper<T> queryWrapper);

  可以通過 queryWrapper拼接自定義參數

  
• 對於一些復雜查詢,連表或者自定義xml等使用 
  mapper接口定義

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

自定義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>

調用

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

結果

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, 一年級一班, 1, 1
<==        Row: 2, 一條螢, 8, 0, 4, 二年級二班, 2, 2
<==      Total: 2
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@5cbe95b1]

 

這種方式需要手動多傳入一個page參數,如果自定義參數較多的情況下可能會比較麻煩.其實mybatis

• 使用一個參數進行分頁

mapper定義

Page<StudentVO> selectStudentInfoPage2(StudentPageDTO studentPageDTO);

xml與上一種方法類似,只是這里只傳入一個參數

 

<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>

調用方法

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, 一年級一班, 1, 1
<==        Row: 2, 一條螢, 8, 0, 4, 二年級二班, 2, 2
<==        Row: 3, 夏海, 9, 0, 5, 二年級三班, 2, 3
<==        Row: 4, 鞠, 10, 0, 10, 五年級一班, 5, 1
<==      Total: 4
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@118fbaf0]

結果

 

 可以看到參數和返回結果是同一對象,可以使用該方式進行分頁的原因很簡單,參數DTO繼承了分頁對象

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

本質上和第一種分頁沒有區別

總結三種分頁本質上都是一樣的,通過攔截器攔截分頁參數,拼接參數

總結下本人知道的三種方式:

1. 使用mp自帶的分頁方法分頁,優點是方便,缺點是不可以自定義xml對於復雜查詢不是很友好

2.自定義xml,傳入多個參數,其中包括一個page對象作為分頁參數

3.自定義參數DTO繼承page對象,傳入該對象也可以作為分頁參數

3可以看成對於2的一種改造,具體使用看取舍