MyBatis：3、级联查询

最新推荐文章于 2025-01-17 06:14:30 发布

小鑫-Chen

最新推荐文章于 2025-01-17 06:14:30 发布

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分类专栏： Spring、SpringMVC、MyBatis、Redis 文章标签： mybatis mysql xml

本文链接：https://blog.youkuaiyun.com/qq_37054755/article/details/115371990

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本文介绍了一对多及多对多关系在MyBatis中的实现方式，包括对应的Java实体类定义、XML映射文件配置以及数据库查询语句。通过具体的例子展示了如何在Student和Classes、Customer和Goods等实体间建立级联查询。

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级联查询

一对多

Student.java：

package com.xiaoxin.entity;

import lombok.Data;

@Data
public class Student {
   private long id;
   private String name;
   private Classes classes;
}

Classes.java：

package com.xiaoxin.entity;

import java.util.List;
import lombok.Data;

@Data
public class Classes {
   private long id;
   private String name;
   private List<Student> students;
}

StudentRepository.java：

package com.xiaoxin.repository;

import com.xiaoxin.entity.Student;

public interface StudentRepository {
    public Student findById(long id);
}

StudentRepository.xml：

<?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.xiaoxin.repository.StudentRepository">

    <resultMap id="StudentMap" type="com.xiaoxin.entity.Student">
        <id column="id" property="id"/>
        <result column="name" property="name"/>
        <association property="classes" javaType="com.xiaoxin.entity.Classes">
            <id column="cid" property="id"/>
            <result column="cname" property="name"/>
        </association>
    </resultMap>

    <select id="findById" parameterType="long" resultMap="StudentMap">
        select s.id, s.name, c.id cid, c.name cname from student s, classes c where  s.cid = c.id and s.id=#{id}
    </select>
</mapper>

config.xml：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <environments default="mydev">
        <environment id="mydev">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useUnicode=true&amp;characterEncoding=utf-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="com/xiaoxin/mapper/AccountMapper.xml"/>
        <mapper resource="com/xiaoxin/repository/AccountRepository.xml"/>
        <mapper resource="com/xiaoxin/repository/StudentRepository.xml"/>
    </mappers>
</configuration>

ClassRepository.java：

package com.xiaoxin.repository;

import com.xiaoxin.entity.Classes;

public interface ClassesRepository {
    public Classes findById(long id);
}

ClassesRepository.xml：

<?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.xiaoxin.repository.ClassesRepository">

    <resultMap id="ClassesMap" type="com.xiaoxin.entity.Classes">
        <id column="cid" property="id"/>
        <result column="cname" property="name"/>
        <collection property="students" ofType="com.xiaoxin.entity.Student">
            <id column="id" property="id"/>
            <result column="name" property="name"/>
        </collection>
    </resultMap>

    <select id="findById" parameterType="long" resultMap="ClassesMap">
        select c.id as cid, c.name as cname, s.id, s.name from student s, classes c where c.id = s.cid and c.id = #{id}
    </select>
</mapper>

config.xml：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <environments default="mydev">
        <environment id="mydev">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useUnicode=true&amp;characterEncoding=utf-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="com/xiaoxin/mapper/AccountMapper.xml"/>
        <mapper resource="com/xiaoxin/repository/AccountRepository.xml"/>
        <mapper resource="com/xiaoxin/repository/StudentRepository.xml"/>
        <mapper resource="com/xiaoxin/repository/ClassesRepository.xml"/>
    </mappers>
</configuration>

多对多

Customer：

package com.xiaoxin.entity;

import lombok.Data;
import java.util.List;

@Data
public class Customer {
    private long id;
    private String name;
    private List<Goods> goodsList;
}

CustomerRepository：

package com.xiaoxin.repository;

import com.xiaoxin.entity.Customer;

public interface CustomerRepository {
    public Customer findById(long id);
}

CustomerRepository.xml：

<?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.xiaoxin.repository.CustomerRepository">
    <resultMap id="CustomerMap" type="com.xiaoxin.entity.Customer">
        <id column="cid" property="id"/>
        <result column="cname" property="name"/>
        <collection property="goodsList" ofType="com.xiaoxin.entity.Goods">
            <id column="gid" property="id"/>
            <result column="gname" property="name"/>
        </collection>
    </resultMap>

   <select id="findById" parameterType="long" resultMap="CustomerMap">
        select c.id cid, c.name cname, g.id gid, g.name gname
        from customer c, goods g, customer_goods cg
        where c.id=cg.cid and g.id=cg.id and c.id=#{id}
    </select>
</mapper>