MyBatisPlus條件構(gòu)造器圖文實例詳解

更新時間：2023年01月31日 10:41:27 作者：Knight_AL

這篇文章主要介紹了MyBatisPlus條件構(gòu)造器，了解內(nèi)部原理是為了幫助我們做擴(kuò)展，同時也是驗證了一個人的學(xué)習(xí)能力，如果你想讓自己的職業(yè)道路更上一層樓，這些底層的東西你是必須要會的

一、wapper介紹

二、AbstractWrapper

注意：以下條件構(gòu)造器的方法入?yún)⒅械?column 均表示數(shù)據(jù)庫字段

1.ge、gt、le、lt、isNull、isNotNull

@Test
public void testSelect() {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.ge("age", 28);
    List<User> users = userMapper.selectList(queryWrapper);
    System.out.println(users);
}

2.eq、ne

注意：seletOne返回的是一條實體記錄，當(dāng)出現(xiàn)多條時會報錯

@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

包含大小邊界

@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：可以實現(xiàn)子查詢

例: inSql(“age”, “1,2,3,4,5,6”)—>age in (1,2,3,4,5,6)
例: 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：這里使用的是 UpdateWrapper

不調(diào)用or則默認(rèn)為使用 and 連

@Test
public void testUpdate1() {
    //修改值
    User user = new User();
    user.setAge(99);
    user.setName("Andy");
    //修改條件
    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o(hù)r、嵌套and

這里使用了lambda表達(dá)式，or中的表達(dá)式最后翻譯成sql時會被加上圓括號

@Test
public void testUpdate2() {
    //修改值
    User user = new User();
    user.setAge(99);
    user.setName("Andy");
    //修改條件
    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：只能調(diào)用一次,多次調(diào)用以最后一次為準(zhǔn) 有sql注入的風(fēng)險,請謹(jǐn)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.指定要查詢的列

@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

最終的sql會合并 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);
    //修改條件
    UpdateWrapper<User> userUpdateWrapper = new UpdateWrapper<>();
    userUpdateWrapper
        .like("name", "h")
        .set("name", "老李頭")//除了可以查詢還可以使用set設(shè)置修改的字段
        .setSql(" email = '123@qq.com'");//可以有子查詢
    int result = userMapper.update(user, userUpdateWrapper);
}