MyBatis-Plus中的LambdaQuery用法实例详解

import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
// 泛型指定实体类型
LambdaQueryWrapper<User> lambdaQuery = new LambdaQueryWrapper<>();

lambdaQuery
    .eq(User::getName, "John")      // WHERE name = 'John'
    .gt(User::getAge, 18)           // AND age > 18
    .like(User::getEmail, "@gmail") // AND email LIKE '%@gmail%'
    .orderByDesc(User::getCreateTime); // ORDER BY create_time DESC

// 注入 Mapper（MyBatis-Plus 的 BaseMapper）
@Autowired
private UserMapper userMapper;
public List<User> queryUsers() {
    return userMapper.selectList(lambdaQuery);
}

public class User {
    private Long id;
    private String name;
    private Integer age;
    private String email;
    private LocalDateTime createTime;
    // 省略 getter/setter
}

lambdaQuery.eq(User::getName, "Alice"); // WHERE name = 'Alice'

lambdaQuery.like(User::getEmail, "hotmail"); // WHERE email LIKE '%hotmail%'

// 查询年龄在 20~30 的用户
lambdaQuery.between(User::getAge, 20, 30); // WHERE age BETWEEN 20 AND 30

lambdaQuery
    .eq(User::getAge, 25)
    .and(q -> q
        .like(User::getName, "Tom")
        .or()
        .eq(User::getEmail, "tom@example.com")
    );
// WHERE age = 25 AND (name LIKE '%Tom%' OR email = 'tom@example.com')

lambdaQuery
    .orderByAsc(User::getAge)    // 年龄升序
    .orderByDesc(User::getId);   // ID降序
// ORDER BY age ASC, id DESC

lambdaQuery
    .select(User::getId, User::getName) // 只查询 id 和 name 字段
    .like(User::getName, "A");
// SELECT id, name FROM user WHERE name LIKE '%A%'

public List<User> queryUsers(String name, Integer minAge) {
    return new LambdaQueryWrapper<User>()
        .eq(StringUtils.isNotBlank(name), User::getName, name)
        .gt(minAge != null, User::getAge, minAge)
        .list();
}
// 当 name 非空时添加 name 条件，当 minAge 非空时添加 age 条件

List<User> users = new LambdaQueryWrapper<User>()
    .like(User::getEmail, "google")
    .ge(User::getAge, 25)         // ge = greater or equal (>=)
    .orderByDesc(User::getCreateTime)
    .last("LIMIT 10")             // 特殊 SQL 拼接
    .list();                      // 执行查询