1 Mybatis-Plus简介

2 使用方法

1  Lambda 表达式执行 SQL

import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import org.springframework.stereotype.Service;
import java.util.List;

@Service
public class UserServiceImpl extends ServiceImpl<UserMapper, User> implements UserService {

    @Override
    public List<User> getUsersByName(String name) {
        LambdaQueryWrapper<User> queryWrapper = new LambdaQueryWrapper<>();
        queryWrapper.eq(User::getName, name);
        return baseMapper.selectList(queryWrapper);
    }
}

2 组合示例 

import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import org.springframework.stereotype.Service;
import java.util.List;

@Service
public class UserServiceImpl extends ServiceImpl<UserMapper, User> implements UserService {

    @Override
    public List<User> getUsersByAge(int minAge, int maxAge) {
        LambdaQueryWrapper<User> queryWrapper = new LambdaQueryWrapper<>();
        queryWrapper.ge(User::getAge, minAge).le(User::getAge, maxAge);
        return baseMapper.selectList(queryWrapper);
    }
}

3 复杂sql  

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.toolkit.Wrappers;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import org.springframework.stereotype.Service;
import java.util.List;
import java.util.Map;

@Service
public class OrderServiceImpl extends ServiceImpl<OrderMapper, Order> implements OrderService {

    @Override
    public List<Map<String, Object>> getOrderAmountByUser() {
        QueryWrapper<Order> queryWrapper = new QueryWrapper<>();
        queryWrapper.select("user_id", "sum(amount) as total_amount")
                    .groupBy("user_id");
        return baseMapper.selectMaps(queryWrapper);
    }
}

3 其他注入sql的方式 

1 使用注解

@Select("SELECT * FROM user WHERE name = #{name}")
List<User> selectByName(@Param("name") String name);

2 使用 XML 映射文件

<?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="selectByName" resultType="User">
        SELECT * FROM user WHERE name = #{name}
    </select>
</mapper>

List<User> selectByName(@Param("name") String name);