MyBatis-Plus UserMpper接口示例实现

package com.example.mapper; // 根据你的项目结构调整包名

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.example.entity.User; // 你的User实体类所在的包
import org.apache.ibatis.annotations.Mapper;

// 使用@Mapper注解让Spring管理这个接口，并生成实现类
@Mapper
public interface UserMapper extends BaseMapper<User> {
    // 不需要写任何方法，就已经继承了BaseMapper中的所有CRUD方法
    
    // 但你也可以根据需要添加自定义方法
}

package com.example.entity;

import com.baomidou.mybatisplus.annotation.TableName;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableField;

// 指定实体类对应的数据库表名
@TableName("user")
public class User {
    // 主键字段
    @TableId
    private Long id;
    
    // 普通字段，如果字段名与数据库列名一致，可以不加注解
    private String name;
    
    private Integer age;
    
    // 如果数据库列名与字段名不一致，可以使用@TableField指定
    @TableField("email_address")
    private String email;
    
    // 省略构造函数、getter和setter方法...
    
    public User() {
    }
    
    public User(Long id, String name, Integer age, String email) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.email = email;
    }
    
    // getter 和 setter 方法
    public Long getId() {
        return id;
    }
    
    public void setId(Long id) {
        this.id = id;
    }
    
    public String getName() {
        return name;
    }
    
    public void setName(String name) {
        this.name = name;
    }
    
    // 其他getter和setter...
}

# 数据源配置
spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/your_database?useUnicode=true&characterEncoding=utf-8&useSSL=false
    username: your_username
    password: your_password

# MyBatis-Plus 配置
mybatis-plus:
  mapper-locations: classpath*:mapper/**/*.xml  # 如果有自定义XML查询文件，指定路径
  type-aliases-package: com.example.entity      # 实体类包路径
  configuration:
    map-underscore-to-camel-case: true          # 自动开启驼峰命名转换
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl # 打印SQL日志

package com.example.service;

import com.example.mapper.UserMapper;
import com.example.entity.User;
import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;

@Service
public class UserService {
    
    @Autowired
    private UserMapper userMapper;
    
    public List<User> getAllUsers() {
        // 查询所有用户
        return userMapper.selectList(null);
    }
    
    public User getUserById(Long id) {
        // 根据ID查询用户
        return userMapper.selectById(id);
    }
    
    public List<User> getUsersByName(String name) {
        // 条件查询：使用Lambda表达式避免硬编码字段名
        LambdaQueryWrapper<User> wrapper = new LambdaQueryWrapper<>();
        wrapper.like(User::getName, name);
        
        return userMapper.selectList(wrapper);
    }
    
    public int addUser(User user) {
        // 插入用户
        return userMapper.insert(user);
    }
    
    public int updateUser(User user) {
        // 更新用户
        return userMapper.updateById(user);
    }
    
    public int deleteUser(Long id) {
        // 删除用户
        return userMapper.deleteById(id);
    }
}

@Mapper
public interface UserMapper extends BaseMapper<User> {
    
    // 自定义查询方法：查询年龄大于指定值的用户
    @Select("SELECT * FROM user WHERE age > #{minAge}")
    List<User> selectUsersOlderThan(@Param("minAge") Integer minAge);
    
    // 或者使用XML配置的方式
    List<User> selectUsersByComplexCondition(Map<String, Object> params);
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.mapper.UserMapper">
    
    <select id="selectUsersByComplexCondition" resultType="com.example.entity.User">
        SELECT * FROM user 
        WHERE name LIKE CONCAT('%', #{name}, '%')
        AND age BETWEEN #{minAge} AND #{maxAge}
    </select>
    
</mapper>