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                ## 一、讓Spring Boot-MybatisPlus支持分頁 在已經集成了Mybatis Plus的Spring項目中加入如下分頁攔截器的配置,讓MybatisPlus支持分頁 ~~~ @Configuration public class MybatisPlusConfiguration { //配置分頁攔截器 @Bean public PaginationInterceptor paginationInterceptor() { return new PaginationInterceptor(); } } ~~~ ## 二、單表查詢分頁-表格分頁 ~~~ @Test public void testSelect() { LambdaQueryWrapper<User> query = new LambdaQueryWrapper<>(); query.ge(User::getAge,10) //查詢條件:年齡大于10 .orderByDesc(User::getAge); //按照年齡的倒序排序 Page<User> page = new Page<> (1,10); //查詢第1頁,每頁10條數據 userMapper.selectPage(page,query); //page分頁信息,query查詢條件 System.out.println("總頁數:"+ page.getPages()); System.out.println("總記錄數:"+ page.getTotal()); // 分頁返回的對象與傳入的對象是同一個 List<User> list = page.getRecords(); list.forEach(System.out::println); } ~~~ 查詢輸出結果如下: ~~~ 總頁數:1 總記錄數:6 User(id=3, name=Tom, age=28, email=test3@baomidou.com) User(id=5, name=Billie, age=24, email=test5@baomidou.com) User(id=4, name=Sandy, age=21, email=test4@baomidou.com) User(id=2, name=Jack, age=20, email=test2@baomidou.com) User(id=1, name=Jone, age=18, email=test1@baomidou.com) User(id=1280261858003038209, name=字母哥, age=18, email=null) ~~~ 在分頁查詢過程中,一共執行了兩條SQL ~~~ # 第一條SQL用于查詢在query條件下的總條數 SELECT COUNT(1) FROM user WHERE age >= ? # 第二條SQL用于查詢具體的數據 SELECT id,name,age,email FROM user WHERE age >= ? ORDER BY age DESC LIMIT ?,? ~~~ 這種分頁方式比較適合于傳統應用中,表格分頁的開發。需要給出總條數,以及每頁多少條。 ![表格分頁查詢](http://cdn.zimug.com/mp3-1.png) ## 三、不查詢總記錄數的分頁-下拉分頁 在一些現代的互聯網資訊網站,或者應用app。通常不會給出數據的總條數,而是通過鼠標或者手勢,每次下拉都加載n條數據。 ![下拉分頁查詢](http://cdn.zimug.com/list-mescroll-lazy.gif) 這種情況下的分頁通常就不需要查詢總條數了,如果查詢總條數浪費數據庫的計算資源,使響應時間變長。所以我們應該只做分頁數據查詢,不查詢總條數。設置page分頁的第三個參數為false。 ![](http://cdn.zimug.com/mp3-2.png) 輸出結果總頁數和總條數都是0,但是分頁數據正常查詢回來了。 ~~~ 總頁數:0 總記錄數:0 User(id=3, name=Tom, age=28, email=test3@baomidou.com) User(id=5, name=Billie, age=24, email=test5@baomidou.com) User(id=4, name=Sandy, age=21, email=test4@baomidou.com) User(id=2, name=Jack, age=20, email=test2@baomidou.com) User(id=1, name=Jone, age=18, email=test1@baomidou.com) User(id=1280261858003038209, name=字母哥, age=18, email=null) ~~~ 只執行了這樣一個SQL ~~~ ELECT id,name,age,email FROM user WHERE age >= ? ORDER BY age DESC LIMIT ?,? ~~~ ## 四、自定義多表聯查并分頁 ~~~ UserVo userVo = new UserVo(); userVo.setAgeStart(25); userVo.setHobby("看書"); Page<User> page = new Page<>(1, 10); userMapper.selectUserPage(page, userVo); System.out.println("總頁數:" + page.getPages()); System.out.println("總記錄數:" + page.getTotal()); List<User> list = page.getRecords(); list.forEach(System.out::println); ~~~ ~~~ SELECT COUNT(1) FROM `user` WHERE age >= ? AND EXISTS ( SELECT 1 FROM `user_hobby` AS ho WHERE ho.user_id = `user`.id AND ho.hobby LIKE CONCAT('%', ?, '%') ) ~~~ ~~~ select * from `user` where age >= ? and EXISTS ( SELECT 1 FROM `user_hobby` as ho where ho.user_id=`user`.id and ho.hobby like CONCAT('%',?,'%') ) LIMIT ?,? ~~~
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