学习视频:【编程不良人】Mybatis-Plus整合SpringBoot实战教程,提高的你开发效率,后端人员必备!
查询方法详解
-
普通查询
// 根据主键id去查询单个结果的。 @Test public void selectById() {User user = userMapper.selectById(1739970502337392641L);System.out.println(user); }//根据多个主键id批量查询结果的 @Test public void selectIds() {List<Long> list = Arrays.asList(1739970502337392641L, 1739983903621038082L, 1739984905459900417L);List<User> userList = userMapper.selectBatchIds(list);userList.forEach(System.out::println); } // 根据多个条件查询结果的 @Test public void selectByMap() {// map.put("name","小明")// map.put("age",30)// 相当于 where name ="小明" and age=30Map<String, Object> columnMap = new HashMap<>();columnMap.put("name", "小刚");columnMap.put("age", "18");List<User> userList = userMapper.selectByMap(columnMap);userList.forEach(System.out::println); }
-
条件构造器查询 【重要】
AbstractWrapper
是 MyBatis Plus 中的一个抽象类,用于构建 SQL 查询条件。定义了泛型T
、C
和Children
。其中,T
表示实体类的类型,C
表示查询条件的类型,Children
表示子类的类型,用于支持链式调用。它提供了一系列方法,用于构建 SQL 查询条件,包括设置查询字段、设置查询条件、排序等。常用实现类包括
QueryWrapper
和UpdateWrapper
。这两个类都是 MyBatis Plus 提供的具体实现,用于构建查询条件和更新条件。 -
条件构造器查询示例
@SpringBootTest public class SelectTests {@Autowiredprivate UserMapper userMapper;/*** 1.名字中包含刘且年龄大于20* name like '%刘%' and age>20*/@Testpublic void selectByWrapper() {// 创建queryWrapper的两种方式QueryWrapper<User> queryWrapper = new QueryWrapper<>(); // QueryWrapper<User> queryWrapper1 = Wrappers.<User>query();queryWrapper.like("name", "刘").gt("age", 20);List<User> list = userMapper.selectList(queryWrapper);list.forEach(System.out::println);}/*** 2.名字中包含刘且年龄大于等于20且小于30并且email不为空* name like ‘%刘’ and age between 20 and 30 and email is not null*/@Testpublic void selectByWrapper2() {QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.like("name", "刘").between("age", 20, 30).isNull("email");List<User> list = userMapper.selectList(queryWrapper);list.forEach(System.out::println);}/*** 3.名字中包含刘或年龄大于等于20,按照年龄降序排序,年龄相同按照id升序排列* name like ‘%刘’ and age between 20 and 30 and email is not null*/@Testpublic void selectByWrapper3() {QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.like("name", "刘").or().ge("age",20).orderByDesc("age").orderByAsc("user_id");List<User> list = userMapper.selectList(queryWrapper);list.forEach(System.out::println);}/*** 4.创建日期为2023年12月17日并且直属上级为王姓* date_format(create_time,'%Y-%m-$d') and manager_id in(select id from user where name like '王%'*/@Testpublic void selectByWrapper4() {QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.apply("date_format(create_time,'%Y-%m-%d')={0}", "2023-12-27") // 使用占位符避免sql注入的风险.inSql("manager_id","select user_id from mp_user where name like '王%'");List<User> list = userMapper.selectList(queryWrapper);list.forEach(System.out::println);}/*** 5.名字为刘姓且年龄小于30或者邮箱不为空* name like '王%' and (age<20 or email is not null)*/@Testpublic void selectByWrapper5() {QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.likeRight("name", "刘").and(wq -> wq.lt("age", 30).or().isNotNull("email"));List<User> list = userMapper.selectList(queryWrapper);list.forEach(System.out::println);}/*** 6.名字为刘姓或者(年龄小于30且大于20并且邮箱不为空)* name like '刘%' or (age<30 and age>20 and email is not null)*/@Testpublic void selectByWrapper6() {QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.likeRight("name", "刘").or(wq -> wq.lt("age", 30).gt("age", 20).isNotNull("email"));List<User> list = userMapper.selectList(queryWrapper);list.forEach(System.out::println);}/*** 7.(年龄小于30且邮箱不为空)并且名字为刘姓* (age<30 or email is not null) and name like '刘%'*/@Testpublic void selectByWrapper7() {QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.nested(wq -> wq.lt("age", 30).or().isNotNull("email")).likeRight("name", "刘");List<User> list = userMapper.selectList(queryWrapper);list.forEach(System.out::println);}/*** 8. 年龄为 21 25 33* age in(21,25,33)*/@Testpublic void selectByWrapper8() {QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.in("age", 21, 25, 33);List<User> list = userMapper.selectList(queryWrapper);list.forEach(System.out::println);}/*** 9. 只返回满足条件的其中一条语句即可* limit 1*/@Testpublic void selectByWrapper9() {QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.in("age", 21, 25, 33).last("limit 1"); // last() 有sql注入的风险,谨慎使用List<User> list = userMapper.selectList(queryWrapper);list.forEach(System.out::println);} }
-
select 不列出全部字段
/*** 10.名字中包含刘且年龄小于30(需求1加强版)*/@Testpublic void selectByWrapper() {QueryWrapper<User> queryWrapper = new QueryWrapper<>(); // queryWrapper.select("user_id","name","age").like("name", "刘").lt("age", 30); // 包含字段queryWrapper.like("name", "刘").lt("age", 30).select(User.class, info ->!info.getColumn().equals("create_time") && !info.getColumn().equals("manager_id"));// 排除字段List<User> list = userMapper.selectList(queryWrapper);list.forEach(System.out::println);}
-
condition作用
根据判断决定查询条件是否加到sql语句里面
@Testpublic void testCondition() {String name = "东";String email = "";condition(name, email);}private void condition(String name, String email) {QueryWrapper<User> queryWrapper = new QueryWrapper<>(); // if (StringUtils.isNotEmpty(name)) { // queryWrapper.like("name", name); // } // if (StringUtils.isNotEmpty(email)) { // queryWrapper.like("email", email); // }queryWrapper.like(StringUtils.isNotEmpty(name), "name", name).like(StringUtils.isNotEmpty(email), "email", email);List<User> list = userMapper.selectList(queryWrapper);list.forEach(System.out::println);}
-
实体作为条件构造器构造方法的参数
@Test public void selectByWrapperEntity() {User user = new User();user.setRealName("小刚");user.setAge(18);QueryWrapper<User> queryWrapper = new QueryWrapper<>(user);List<User> list = userMapper.selectList(queryWrapper);list.forEach(System.out::println); } 运行结果的sql语句:SELECT * FROM mp_user WHERE **name=? AND age=?** 会把set注入的属性和值映射到where条件中
-
通过
SqlCondition
更改查询条件用法 @TableField(condition = SqlCondition.LIKE) private String name; @TableField(condition = "%s<#{%s}") //根据定义的常量,自己也可以参考并更改 private Integer age; 运行结果:SELECT * FROM mp_user WHERE **name LIKE CONCAT('%',?,'%')** AND AND age<?
-
-
allEq
**
allEq
**是一个查询条件配置方法,用于构建查询条件。它可以根据传入的条件参数,生成一个包含所有等值条件的查询条件对象。@Test public void selectByWrapperAllEq() {QueryWrapper<User> queryWrapper = new QueryWrapper<>();Map<String, Object> params = new HashMap<>();params.put("name", "小明");params.put("age", null);**queryWrapper.allEq(params,false)**; // false代表忽略值为null的字段,即不参与where条件List<User> list = userMapper.selectList(queryWrapper);list.forEach(System.out::println); }
-
其他条件构造器
**selectMaps
返回**@Testpublic void selectByWrapperMaps() {QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.select("user_id","name").like("name", "刘").lt("age", 30); // List<User> list = userMapper.selectList(queryWrapper);// 返回值为实体类的话,没设置的值还是会返回,只不过值为nullList<Map<String, Object>> userList = userMapper.selectMaps(queryWrapper);// 只返回限定的字段userList.forEach(System.out::println);}/** 示例* 11.按照直属上级分组,查询每组的平均年龄、最大年龄、最小年龄,并且至取年龄总和为500的组* select avg(age)avg_age,min(age) min_age,max(age) max_age from user group by manager_id having sum(age)<500*/@Testpublic void selectByWrapperMaps2() {QueryWrapper<User> queryWrapper = new QueryWrapper<>();queryWrapper.select("avg(age) avg_age", "min(age) min_age", "max(age) max_age").groupBy("manager_id").having("sum(age)<{0}", 500);List<Map<String, Object>> userList = userMapper.selectMaps(queryWrapper);userList.forEach(System.out::println);}
-
lambda条件构造器
@Test public void selectLambda() {//创建lambda条件构造器的三种方式LambdaQueryWrapper<User> lambda = new LambdaQueryWrapper<>();LambdaQueryWrapper<User> lambda2 = new QueryWrapper<User>().lambda();LambdaQueryWrapper<User> lambda3= Wrappers.<User>lambdaQuery();lambda3.like(User::getName, "刘").lt(User::getAge, 30); // where name like '%雨%' and age<30List<User> userList = userMapper.selectList(lambda3);userList.forEach(System.out::println); } /*** 5.名字为刘姓且(年龄小于30或邮箱不为空)* name like '刘%' and (age<30 or email is not null)*/ @Test public void selectLambda2() {LambdaQueryWrapper<User> lambda= Wrappers.<User>lambdaQuery();lambda.like(User::getName, "刘").and(wq -> wq.lt(User::getAge, 20).or().isNotNull(User::getEmail));List<User> userList = userMapper.selectList(lambda);userList.forEach(System.out::println); } // 链式调用多个条件 LambdaQueryChainWrapper @Test public void selectLambda3() {List<User> userList = new LambdaQueryChainWrapper<>(userMapper).like(User::getName, "刘").ge(User::getAge, 20).list();userList.forEach(System.out::println); }
下一章:Spring Boot学习随笔- 集成MyBatis-Plus(三)自定义SQL、分页实现(PaginationInterceptor )、更新和删除详细方法