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MybatisPlus进阶(二)

哒卟刘先生
2022-01-10 / 0 评论 / 0 点赞 / 104 阅读 / 6,000 字 / 正在检测是否收录...
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条件构造器

上一篇讲了MybatisPlus的CRUD,这一篇说一下它的构造器,也是它比较好用的一个地方,一些稍微复杂的数据库操作也可以用构造器生成mapper。话不多说上代码

一、wapper介绍

在这里插入图片描述

Wrapper : 条件构造抽象类,最顶端父类 AbstractWrapper : 用于查询条件封装,生成 sql 的 where 条件 QueryWrapper : Entity 对象封装操作类,不是用lambda语法 UpdateWrapper : Update 条件封装,用于Entity对象更新操作 AbstractLambdaWrapper : Lambda 语法使用 Wrapper统一处理解析 lambda 获取 column。 LambdaQueryWrapper :看名称也能明白就是用于Lambda语法使用的查询Wrapper LambdaUpdateWrapper : Lambda 更新封装Wrapper

@RunWith(SpringRunner.class)
@SpringBootTest
public class QueryWrapperTests {
    
    @Autowired
    private UserMapper userMapper;
}

二、AbstractWrapper

注意:以下条件构造器的方法入参中的 column 均表示数据库字段

1、ge、gt、le、lt、isNull、isNotNull

@Test
public void testDelete() {
​
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper
        .isNull("name")
        .ge("age", 12)
        .isNotNull("email");
    int result = userMapper.delete(queryWrapper);
    System.out.println("delete return count = " + result);
}

SQL:UPDATE user SET deleted=1 WHERE deleted=0 AND name IS NULL AND age >= ? AND email IS NOT NULL

2、eq、ne

注意:seletOne返回的是一条实体记录,当出现多条时会报错

@Test
public void testSelectOne() {
​
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.eq("name", "Tom");
​
    User user = userMapper.selectOne(queryWrapper);
    System.out.println(user);
}

SELECT id,name,age,email,create_time,update_time,deleted,version FROM user WHERE deleted=0 AND name = ?

3、between、notBetween

包含大小边界

@Test
public void testSelectCount() {
​
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.between("age", 20, 30);
​
    Integer count = userMapper.selectCount(queryWrapper);
    System.out.println(count);
}

SELECT COUNT(1) FROM user WHERE deleted=0 AND age BETWEEN ? AND ?

4、allEq

@Test
public void testSelectList() {
​
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    Map<String, Object> map = new HashMap<>();
    map.put("id", 2);
    map.put("name", "Jack");
    map.put("age", 20);
​
    queryWrapper.allEq(map);
    List<User> users = userMapper.selectList(queryWrapper);
​
    users.forEach(System.out::println);
}

SELECT id,name,age,email,create_time,update_time,deleted,version
FROM user WHERE deleted=0 AND name = ? AND id = ? AND age = ?

5、like、notLike、likeLeft、likeRight

selectMaps返回Map集合列表

@Test
public void testSelectMaps() {
​
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper
        .notLike("name", "e")
        .likeRight("email", "t");
​
    List<Map<String, Object>> maps = userMapper.selectMaps(queryWrapper);//返回值是Map列表
    maps.forEach(System.out::println);
}

SELECT id,name,age,email,create_time,update_time,deleted,version
FROM user WHERE deleted=0 AND name NOT LIKE ? AND email LIKE ?

6、in、notIn、inSql、notinSql、exists、notExists

in、notIn:

  • notIn("age",{1,2,3})--->age not in (1,2,3)
  • notIn("age", 1, 2, 3)--->age not in (1,2,3)

inSql、notinSql:可以实现子查询

  • inSql("age", "1,2,3,4,5,6")--->age in (1,2,3,4,5,6)
  • inSql("id", "select id from table where id < 3")--->id in (select id from table where id < 3)
  @Test
        public void testSelectObjs() {
        ​
            QueryWrapper<User> queryWrapper = new QueryWrapper<>();
            //queryWrapper.in("id", 1, 2, 3);
            queryWrapper.inSql("id", "select id from user where id < 3");
        ​
            List<Object> objects = userMapper.selectObjs(queryWrapper);//返回值是Object列表
            objects.forEach(System.out::println);
        }

SELECT id,name,age,email,create_time,update_time,deleted,version
FROM user WHERE deleted=0 AND id IN (select id from user where id < 3)

7、or、and

注意:这里使用的是 UpdateWrapper
不调用or则默认为使用 and 连

@Test
public void testUpdate1() {
​
    //修改值
    User user = new User();
    user.setAge(99);
    user.setName("Andy");
​
    //修改条件
    UpdateWrapper<User> userUpdateWrapper = new UpdateWrapper<>();
    userUpdateWrapper
        .like("name", "h")
        .or()
        .between("age", 20, 30);
​
    int result = userMapper.update(user, userUpdateWrapper);
​
    System.out.println(result);
}

UPDATE user SET name=?, age=?, update_time=? WHERE deleted=0 AND name LIKE ? OR age BETWEEN ? AND ?

8、嵌套or、嵌套and

这里使用了lambda表达式,or中的表达式最后翻译成sql时会被加上圆括号

@Test
public void testUpdate2() {
​
​
    //修改值
    User user = new User();
    user.setAge(99);
    user.setName("Andy");
​
    //修改条件
    UpdateWrapper<User> userUpdateWrapper = new UpdateWrapper<>();
    userUpdateWrapper
        .like("name", "h")
        .or(i -> i.eq("name", "李白").ne("age", 20));
​
    int result = userMapper.update(user, userUpdateWrapper);
​
    System.out.println(result);
}

UPDATE user SET name=?, age=?, update_time=?
WHERE deleted=0 AND name LIKE ?
OR ( name = ? AND age <> ? )

9、orderBy、orderByDesc、orderByAsc

@Test
public void testSelectListOrderBy() {
​
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.orderByDesc("id");
​
    List<User> users = userMapper.selectList(queryWrapper);
    users.forEach(System.out::println);
}

SELECT id,name,age,email,create_time,update_time,deleted,version
FROM user WHERE deleted=0 ORDER BY id DESC

10、last

直接拼接到 sql 的最后

注意:只能调用一次,多次调用以最后一次为准 有sql注入的风险,请谨慎使用

@Test
public void testSelectListLast() {
​
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.last("limit 1");
​
    List<User> users = userMapper.selectList(queryWrapper);
    users.forEach(System.out::println);
}

SELECT id,name,age,email,create_time,update_time,deleted,version
FROM user WHERE deleted=0 limit 1

11、指定要查询的列

@Test
public void testSelectListColumn() {
​
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.select("id", "name", "age");
​
    List<User> users = userMapper.selectList(queryWrapper);
    users.forEach(System.out::println);
}

SELECT id,name,age FROM user WHERE deleted=0

12、set、setSql

最终的sql会合并 user.setAge(),以及 userUpdateWrapper.set() 和 setSql() 中 的字段

@Test
public void testUpdateSet() {
​
    //修改值
    User user = new User();
    user.setAge(99);
​
    //修改条件
    UpdateWrapper<User> userUpdateWrapper = new UpdateWrapper<>();
    userUpdateWrapper
        .like("name", "h")
        .set("name", "老李头")//除了可以查询还可以使用set设置修改的字段
        .setSql(" email = '123@qq.com'");//可以有子查询
​
    int result = userMapper.update(user, userUpdateWrapper);
}

UPDATE user SET age=?, update_time=?, name=?, email = '123@qq.com' WHERE deleted=0 AND name LIKE ?

最具挑战性的挑战莫过于提升自我。——迈克尔·F·斯特利

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