Mybatis单向多对一

Posted 2020-10-24 墨阳

一、假定一个父母有多个孩子，那父母和孩子对应关系为1对多。

二、 1、添加依赖包，参考上篇文章 Mybatis+mysql入门使用

        2、初始化数据库和初始数据，以mysql为例

DROP DATABASE IF EXISTS moy_mybatis;
CREATE DATABASE moy_mybatis CHARACTER SET UTF8;
USE moy_mybatis;

DROP TABLE  IF EXISTS t_children;
CREATE TABLE t_children(
  children_id INT(11),
  children_name VARCHAR(50) DEFAULT NULL,
  children_birthday DATE DEFAULT NULL,
  parent_id INT(11) NOT NULL,
  PRIMARY KEY (`children_id`)
);

DROP TABLE  IF EXISTS t_parent;
CREATE TABLE t_parent(
  id INT(11)  ,
  name VARCHAR(50) DEFAULT NULL,
  birthday DATE DEFAULT NULL,
  PRIMARY KEY (id)
);

INSERT INTO t_children(children_id,children_name,children_birthday,parent_id)
VALUES (1,\'一号熊孩子\',now(),1);
INSERT INTO t_children(children_id,children_name,children_birthday,parent_id)
VALUES (2,\'二号熊孩子\',now(),1);
INSERT INTO t_children(children_id,children_name,children_birthday,parent_id)
VALUES (3,\'三号熊孩子\',now(),2);

INSERT INTO t_parent(id,name,birthday)
VALUES (1,\'一号父母\',now());
INSERT INTO t_parent(id,name,birthday)
VALUES (2,\'二号父母\',now());

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       3、新建实体类Children和Parent

package com.moy.mybatis3.entity;

import java.util.Date;

/**
 * [Project]:moy-gradle-project  <br/>
 * [Email]:[e-mail]  <br/>
 * [Date]:2018/2/19  <br/>
 * [Description]:  <br/>
 *
 * @author YeXiangYang
 */
public class Children {

    private int childrenId;
    private String childrenName;
    private Date childrenBirthday;

    public int getChildrenId() {
        return childrenId;
    }

    public void setChildrenId(int childrenId) {
        this.childrenId = childrenId;
    }

    public String getChildrenName() {
        return childrenName;
    }

    public void setChildrenName(String childrenName) {
        this.childrenName = childrenName;
    }

    public Date getChildrenBirthday() {
        return childrenBirthday;
    }

    public void setChildrenBirthday(Date childrenBirthday) {
        this.childrenBirthday = childrenBirthday;
    }

    @Override
    public String toString() {
        return "Children{" +
                "childrenId=" + childrenId +
                ", childrenName=\'" + childrenName + \'\\\'\' +
                ", childrenBirthday=" + childrenBirthday +
                \'}\';
    }
}

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package com.moy.mybatis3.entity;

import java.util.Date;
import java.util.List;

/**
 * [Project]:moy-gradle-project  <br/>
 * [Email]:[e-mail]  <br/>
 * [Date]:2018/2/19  <br/>
 * [Description]:  <br/>
 *
 * @author YeXiangYang
 */
public class Parent {

    private int id;
    private String name;
    private Date birthday;
    private List<Children> children;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public List<Children> getChildren() {
        return children;
    }

    public void setChildren(List<Children> children) {
        this.children = children;
    }

    @Override
    public String toString() {
        return "Parent{" +
                "id=" + id +
                ", name=\'" + name + \'\\\'\' +
                ", birthday=" + birthday +
                ", children=" + children +
                \'}\';
    }
}

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      4、新建实体对应配置文件Children.xml和Parent.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.moy.mybatis3.mapper.ChildrenMapper">
    <!--单向多对1 配置方法一 开始-->
    <resultMap id="ChildrenResultMap" type="Children">
        <id property="childrenId" column="children_id"/>
        <result property="childrenName" column="children_name"/>
        <result property="childrenBirthday" column="children_birthday"/>
    </resultMap>
    <!--单向多对1 配置方法一 结束-->
</mapper>

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<?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.moy.mybatis3.mapper.ParentMapper">
    <!--单向多对1 配置方法一 开始-->
    <!--<resultMap id="ParentResultMap" type="Parent">-->
        <!--<id property="id" column="id"/>-->
        <!--<result property="name" column="name"/>-->
        <!--<result property="birthday" column="birthday"/>-->
        <!--<collection property="children" resultMap="com.moy.mybatis3.mapper.ChildrenMapper.ChildrenResultMap"/>-->
    <!--</resultMap>-->
    <!--单向多对1 配置方法一 结束-->

    <!--单向多对1 配置方法二 开始-->
    <resultMap id="ParentResultMap" type="Parent">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="birthday" column="birthday"/>
        <collection property="children"  ofType="Children" >
            <id property="childrenId" column="children_id"/>
            <result property="childrenName" column="children_name"/>
            <result property="childrenBirthday" column="children_birthday"/>
        </collection>
    </resultMap>
    <!--单向多对1 配置方法二 结束-->

    <select id="queryParentAndChildren" parameterType="int" resultMap="ParentResultMap">
          SELECT * FROM t_Parent p LEFT JOIN t_Children c  ON  p.id = c.parent_id WHERE 1=1 AND p.id  = #{id}
    </select>
</mapper>

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      5、编写接口ParentMapper

package com.moy.mybatis3.mapper;

import com.moy.mybatis3.entity.Parent;

/**
 * [Project]:moy-gradle-project  <br/>
 * [Email]:[e-mail]  <br/>
 * [Date]:2018/2/19  <br/>
 * [Description]:  <br/>
 *
 * @author YeXiangYang
 */
public interface ParentMapper extends BaseMapper<Parent> {

    Parent queryParentAndChildren(int id);
}

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      6、为了方便测试，编写一个获取SqlSession的工具类Mybatis3Utils

package com.moy.mybatis3.utils;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.Reader;
import java.util.Objects;

/**
 * [Project]:moy-gradle-project  <br/>
 * [Email]:[e-mail]  <br/>
 * [Date]:2018/2/19  <br/>
 * [Description]:  <br/>
 *
 * @author YeXiangYang
 */
public abstract class Mybatis3Utils {

    public static final SqlSessionFactory sqlSessionFactory;
    public static final ThreadLocal<SqlSession> sessionThread = new ThreadLocal<>();

    static {
        try {
            Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public static SqlSession getCurrentSqlSession() {
        SqlSession sqlSession = sessionThread.get();
        if (Objects.isNull(sqlSession)) {
            sqlSession = sqlSessionFactory.openSession();
            sessionThread.set(sqlSession);
        }
        return sqlSession;
    }

    public static void closeCurrentSession() {
        SqlSession sqlSession = sessionThread.get();
        if (Objects.nonNull(sqlSession)) {
            sqlSession.close();
        }
        sessionThread.set(null);
    }
}

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     7、新建mybatis配置信息文件mybatis-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>
    <typeAliases>
        <package name="com.moy.mybatis3.entity"/>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://127.0.0.1:3306/moy_mybatis?useSSL=false"/>
                <property name="username" value="root"/>
                <property name="password" value="123"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="mapper/Parent.xml"></mapper>
        <mapper resource="mapper/Children.xml"></mapper>
    </mappers>
</configuration>

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     8、编写测试类ParentMapperTest

package com.moy.mybatis3.mapper;

import com.moy.mybatis3.entity.Children;
import com.moy.mybatis3.entity.Parent;
import com.moy.mybatis3.utils.Mybatis3Utils;
import org.apache.ibatis.session.SqlSession;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import java.util.List;

import static org.junit.Assert.*;

/**
 * [Project]:moy-gradle-project  <br/>
 * [Email]:[e-mail]  <br/>
 * [Date]:2018/2/20  <br/>
 * [Description]:  <br/>
 *
 * @author YeXiangYang
 */
public class ParentMapperTest {

    SqlSession sqlSession;
    ParentMapper parentMapper;

    @Before
    public void before() {
        sqlSession = Mybatis3Utils.getCurrentSqlSession();
        parentMapper = sqlSession.getMapper(ParentMapper.class);
    }

    @After
    public void after() {
        Mybatis3Utils.closeCurrentSession();
    }

    @Test
    public void queryParentAndChildren() {
        Parent parent = parentMapper.queryParentAndChildren(1);
        System.out.println(parent);
    }
}

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