一、引言

那么那么那么今天来说下MP中强大的条件查询功能。

本章是基于上个案例来讲的：MyBaits-Plus 快速入门案例

二、具体操作

首先来说说基本的查询吧，根据主键或者简单的查询条件进行查询。

/** * 通过单个ID主键进行查询 */ @Test public void selectById() { User user = userMapper.selectById(1094592041087729666L); System.out.println(user); } /** * 通过多个ID主键查询 */ @Test public void selectByList() { List<Long> longs = Arrays.asList(1094592041087729666L, 1094590409767661570L); List<User> users = userMapper.selectBatchIds(longs); users.forEach(System.out::println); } /** * 通过Map参数进行查询 */ @Test public void selectByMap() { Map<String, Object> params = new HashMap<>(); params.put("name", "张雨琪"); List<User> users = userMapper.selectByMap(params); users.forEach(System.out::println); }

MyBatis-Plus还提供了Wrapper条件构造器，具体使用看如下代码：

/** * 名字包含雨并且年龄小于40 * <p> * WHERE name LIKE '%雨%' AND age < 40 */ @Test public void selectByWrapperOne() { QueryWrapper<User> wrapper = new QueryWrapper(); wrapper.like("name", "雨").lt("age", 40); List<User> users = userMapper.selectList(wrapper); users.forEach(System.out::println); } /** * 名字包含雨 * 年龄大于20小于40 * 邮箱不能为空 * <p> * WHERE name LIKE '%雨%' AND age BETWEEN 20 AND 40 AND email IS NOT NULL */ @Test public void selectByWrapperTwo() { QueryWrapper<User> wrapper = Wrappers.query(); wrapper.like("name", "雨").between("age", 20, 40).isNotNull("email"); List<User> users = userMapper.selectList(wrapper); users.forEach(System.out::println); } /** * 名字为王性 * 或者年龄大于等于25 * 按照年龄降序排序，年龄相同按照id升序排序 * <p> * WHERE name LIKE '王%' OR age >= 25 ORDER BY age DESC , id ASC */ @Test public void selectByWrapperThree() { QueryWrapper<User> wrapper = Wrappers.query(); wrapper.likeRight("name", "王").or() .ge("age", 25).orderByDesc("age").orderByAsc("id"); List<User> users = userMapper.selectList(wrapper); users.forEach(System.out::println); } /** * 查询创建时间为2019年2月14 * 并且上级领导姓王 * <p> * WHERE date_format(create_time,'%Y-%m-%d') = '2019-02-14' AND manager_id IN (select id from user where name like '王%') */ @Test public void selectByWrapperFour() { QueryWrapper<User> wrapper = Wrappers.query(); wrapper.apply("date_format(create_time,'%Y-%m-%d') = {0}", "2019-02-14") .inSql("manager_id", "select id from user where name like '王%'"); List<User> users = userMapper.selectList(wrapper); users.forEach(System.out::println); } /** * 查询王姓 * 并且年龄小于40或者邮箱不为空 * <p> * WHERE name LIKE '王%' AND ( age < 40 OR email IS NOT NULL ) */ @Test public void selectByWrapperFive() { QueryWrapper<User> wrapper = Wrappers.query(); wrapper.likeRight("name", "王").and(qw -> qw.lt("age", 40).or().isNotNull("email")); List<User> users = userMapper.selectList(wrapper); users.forEach(System.out::println); } /** * 查询王姓 * 并且年龄大于20 、年龄小于40、邮箱不能为空 * <p> * WHERE name LIKE ? OR ( age BETWEEN ? AND ? AND email IS NOT NULL ) */ @Test public void selectByWrapperSix() { QueryWrapper<User> wrapper = Wrappers.query(); wrapper.likeRight("name", "王").or( qw -> qw.between("age", 20, 40).isNotNull("email") ); List<User> users = userMapper.selectList(wrapper); users.forEach(System.out::println); } /** * (年龄小于40或者邮箱不为空) 并且名字姓王 * WHERE ( age < 40 OR email IS NOT NULL ) AND name LIKE '王%' */ @Test public void selectByWrapperSeven() { QueryWrapper<User> wrapper = Wrappers.query(); wrapper.nested(qw -> qw.lt("age", 40).or().isNotNull("email")) .likeRight("name", "王"); List<User> users = userMapper.selectList(wrapper); users.forEach(System.out::println); } /** * 查询年龄为30、31、32 * WHERE age IN (?,?,?) */ @Test public void selectByWrapperEight() { QueryWrapper<User> wrapper = Wrappers.query(); wrapper.in("age", Arrays.asList(30, 31, 32)); List<User> users = userMapper.selectList(wrapper); users.forEach(System.out::println); } /** * 查询一条数据 * limit 1 */ @Test public void selectByWrapperNine() { QueryWrapper<User> wrapper = Wrappers.query(); wrapper.in("age", Arrays.asList(30, 31, 32)).last("limit 1"); List<User> users = userMapper.selectList(wrapper); users.forEach(System.out::println); }

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