Mybatis 復雜對象resultMap的使用

Posted on 2021-08-25 by WalkonNet

Mybatis 復雜對象resultMap

數據對象含有普通屬性，一對一對象，一對多對象（2種情況：單一主鍵和復合主鍵）

下面是resultMap的定義

 <resultMap id="GoodsResultMap" type="GoodsModelCustomize">
        <id property="goods_cd" column="goods_cd" />
        <result property="production_company_cd" column="production_company_cd" />
        <result property="production_place_cd" column="production_place_cd" />
        <result property="goods_nm_jp" column="goods_nm_jp" />
        <result property="goods_nm_en" column="goods_nm_en" />
        <result property="goods_nm_zh" column="goods_nm_zh" />
        <result property="goods_type" column="goods_type" />
        <result property="goods_package" column="goods_package" />
        <result property="upd_dttm" column="upd_dttm" />
		<association property="productioncompany" column="production_company_cd" javaType="trade.db.model.Productioncompany">
			<id property="production_company_cd" column="production_company_cd"/>
			<result property="company_nm_jp" column="company_nm_jp"/>
			<result property="company_rnm_jp" column="company_rnm_jp"/>
		</association>
		<collection property="goodsnutrientList" column="goods_cd" ofType="trade.db.model.Goodsnutrient" select="getGoodsnutrient" />
		<collection property="liquorgoodsccicList" column="goods_cd" ofType="trade.db.model.Liquorgoodsccic" select="getLiquorgoodsccic">
       		<id property="goods_cd" column="goods_cd" />
			<id property="ccic_item_cd" column="ccic_item_cd"/>
			<result property="ccic_item_val1" column="ccic_item_val1"/>
		</collection>
		<collection property="projectgoodsList" column="goods_cd" ofType="trade.db.model.Projectgoods" select="getProjectgoods">
			<id property="project_goods_cd" column="project_goods_cd"/>
			<result property="project_cd" column="project_cd"/>
			<result property="goods_cd" column="goods_cd"/>
		</collection>
    </resultMap>
    <resultMap id="GoodsnutrientResultMap" type="Goodsnutrient">
        <id property="goods_cd" column="goods_cd" />
        <id property="nutrient_item_cd" column="nutrient_item_cd" />
        <result property="sort_no" column="sort_no" />
        <result property="nutrient_value" column="nutrient_value" />
        <result property="nutrient_nrv" column="nutrient_nrv" />
        <result property="upd_dttm" column="upd_dttm" />
    </resultMap>

普通屬性省略說明

一對一屬性productioncompany
一對多屬性goodsnutrientList（復合主鍵，返回的復雜對象內有數據）
一對多屬性liquorgoodsccicList（復合主鍵，返回的復雜對象內沒有數據）
一對多屬性projectgoodsList（單一主鍵，返回的復雜對象內有數據）

select相關配置

    <select id="getGoodsnutrient" parameterType="String" resultMap="GoodsnutrientResultMap">
        SELECT 
        	m_goods_nutrient.*
        FROM m_goods_nutrient
        <where>
        	m_goods_nutrient.goods_cd = #{goods_cd}
        	AND m_goods_nutrient.del_flg = '0'
        </where>
    </select>
    <select id="getLiquorgoodsccic" parameterType="String" resultType="trade.db.model.Liquorgoodsccic">
        SELECT 
        	m_liquorgoods_ccic.*
        FROM m_liquorgoods_ccic
        <where>
        	m_liquorgoods_ccic.goods_cd = #{goods_cd}
        	AND m_liquorgoods_ccic.del_flg = '0'
        </where>
    </select>
   <select id="getProjectgoods" parameterType="String" resultType="trade.db.model.Projectgoods">
        SELECT 
        	t_project_goods.*
        FROM t_project_goods
        <where>
        	t_project_goods.goods_cd = #{goods_cd}
        	AND t_project_goods.del_flg = '0'
        </where>
    </select>
   <select id="findByPrimaryKey" parameterType="String" resultMap="GoodsResultMap">
        SELECT 
            m_goods.*,
        	m_production_company.*,
            now() AS SELECT_TIME
        FROM m_goods
        LEFT JOIN
        	m_production_company
        	ON m_goods.production_company_cd = m_production_company.production_company_cd
        	AND m_production_company.del_flg = '0'
        WHERE
              m_goods.goods_cd = #{primary_key}
        	AND m_goods.del_flg = '0'
    </select>

通過findByPrimaryKey方法獲取普通屬性和1對1對象屬性
通過getGoodsnutrient方法獲取1對多復合主鍵的屬性，註意返回類型的配置為resultMap=“GoodsnutrientResultMap”（返回的對象的List屬性內有數據）
通過getLiquorgoodsccic方法獲取1對多復合主鍵的屬性，此處的返回類型為 resultType=“trade.db.model.Liquorgoodsccic”（返回的對象的List屬性內沒有數據）
通過getProjectgoods方法獲取1對多單一主鍵的屬性，此處的返回類型為resultType=“trade.db.model.Projectgoods”（返回的對象的List屬性內有數據）

Model代碼

public class GoodsModelCustomize extends Goods {
	/**
	 * 製造會社
	 */
	private Productioncompany productioncompany;
	public Productioncompany getProductioncompany() {
		return productioncompany;
	}
	public void setProductioncompany(Productioncompany productioncompany) {
		this.productioncompany = productioncompany;
	}
	/**
	 * 商品栄養成分
	 */
	private List<Goodsnutrient> goodsnutrientList;
	public List<Goodsnutrient> getGoodsnutrientList() {
		return goodsnutrientList;
	}
	public void setGoodsnutrientList(List<Goodsnutrient> goodsnutrientList) {
		this.goodsnutrientList = goodsnutrientList;
	}
	/**
	 * 酒類商品CCIC
	 */
	private List<Liquorgoodsccic> liquorgoodsccicList;
	public List<Liquorgoodsccic> getLiquorgoodsccicList() {
		return liquorgoodsccicList;
	}
	public void setLiquorgoodsccicList(List<Liquorgoodsccic> liquorgoodsccicList) {
		this.liquorgoodsccicList = liquorgoodsccicList;
	}
	/**
	 * 項目商品列表
	 */
	private List<Projectgoods> projectgoodsList;
	public List<Projectgoods> getProjectgoodsList() {
		return projectgoodsList;
	}
	public void setProjectgoodsList(List<Projectgoods> projectgoodsList) {
		this.projectgoodsList = projectgoodsList;
	}
}

普通屬性繼承與Goods代碼省略，上述屬性productioncompany，goodsnutrientList和projectgoodsList有數據，但是liquorgoodsccicList沒有數據

因此，當返回對象內有1對多的List屬性，同時此list為復合主鍵的話，推薦使用resultMap來對返回數據映射。

resultMap處理復雜映射問題

在這裡插入圖片描述

association:關聯（多對一的情況）
collection: 集合（一對多的情況）
javaType: 用來指定實體類中屬性的類型。
ofType: 用來指定映射到List或集合中POJO的類型，泛型的約束類型。

Ⅰ 多對一查詢：學生——老師

數據庫表：

CREATE TABLE `teacher` (
`id` INT(10) NOT NULL,
`name` VARCHAR(30) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8;
INSERT INTO teacher(`id`, `name`) VALUES (1, '王老師');
CREATE TABLE `student` (
`id` INT(10) NOT NULL,
`name` VARCHAR(30) DEFAULT NULL,
`tid` INT(10) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `fktid` (`tid`),
CONSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8;
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('1', '小明', '1');
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('2', '小紅', '1');
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('3', '小張', '1');
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('4', '小李', '1');
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('5', '小王', '1');

在這裡插入圖片描述

(1) 創建實體類POJO

@Data
public class Student {
    private int id;
    private String name;
    private Teacher teacher;
}

@Data
public class Teacher {
    private int id;
    private String name;
}

(2) 創建學生實體類對應的接口

public interface StudentMapper {
    //查詢所有學生的信息
    List<Student> getStudent();
    List<Student> getStudent2();
}

(3) 編寫學生接口對應的Mapper.xml

為瞭達到和接口在同一個包中的效果，在resource文件夾下新建包結構com.glp.dao:

在這裡插入圖片描述

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.glp.dao.StudentMapper">
<!--按照結果查詢——聯表查詢-->
    <select id="getStudent2" resultMap="StudentMap2">
         select s.id sid,s.name sname,t.name tname from student s, teacher t where s.tid=t.id;
    </select>
    <resultMap id="StudentMap2" type="Student">
         <result property="id" column="sid"/>
         <result property="name" column="sname"/>
        <association property="teacher" javaType="Teacher">
            <result property="name" column="tname"/>
        </association>
    </resultMap>
    <!--按照查詢嵌套處理——子查詢-->
        <select id="getStudent" resultMap="StudentMap" >
           select * from student;
        </select>
    <resultMap id="StudentMap" type="Student">
        <result property="id" column="id"/>
        <result property="name" column="name"/>
        <!--復雜屬性：對象association, 集合collection-->
        <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
    </resultMap>
        
        <select id="getTeacher" resultType="Teacher">
            select * from teacher where id = #{id};
        </select>
</mapper>

在多對一查詢中，需要用到teacher這個表，每個學生都對應著一個老師。而property隻能處理單個屬性，像teacher這種復雜屬性（內含多個屬性）需要進行處理。處理復雜對象要用association 。

方式一：聯表查詢（直接查出所有信息，再對結果進行處理）

   <resultMap id="StudentMap2" type="Student">
         <result property="id" column="sid"/>
         <result property="name" column="sname"/>
        <association property="teacher" javaType="Teacher">
            <result property="name" column="tname"/>
        </association>
    </resultMap>

直接查詢出學生和老師，然後用association去取老師裡面的屬性property。

方式二：子查詢（先查出學生信息，再拿著學生中的tid，去查詢老師的信息）

  <resultMap id="StudentMap" type="Student">
        <result property="id" column="id"/>
        <result property="name" column="name"/>
        <!--復雜屬性：對象association-->
        <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
    </resultMap>
        
        <select id="getTeacher" resultType="Teacher">
            select * from teacher where id = #{id};
        </select>

在resultMap中引入屬性association，通過javaType指定property=”teacher”的類型，javaType=”Teacher”。通過select引入子查詢（嵌套查詢）。

在這裡插入圖片描述

這裡是拿到學生中的tid，去查找對應的老師。

（4）在核心配置類中引入Mapper

db.properties:數據庫連接參數配置文件

driver = com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&chracterEncoding=utf8
username =root
password =mysql

mybatis.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>
    <properties resource="db.properties">
        <property name="username" value="root"/>
        <property name="password" value="mysql"/>
    </properties>
    <settings>
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>
    <typeAliases>
        <typeAlias type="com.glp.POJO.Student" alias="Student"/>
        <typeAlias type="com.glp.POJO.Teacher" alias="Teacher"/>
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper class="com.glp.dao.StudentMapper"/>
        <mapper class="com.glp.dao.TeacherMapper"/>
    </mappers>
</configuration>

註意：

要保證接口和Mapper.xml都在同一個包中。

(5) 測試

public class UserDaoTest {
    @Test
    public void getStudent(){
        SqlSession sqlSession = MyUtils.getSqlSession();
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        List<Student> list = mapper.getStudent();
        for (Student stu:list ) {
            System.out.println(stu);
        }
        sqlSession.close();
    }
    @Test
    public void getStudent2(){
        SqlSession sqlSession = MyUtils.getSqlSession();
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        List<Student> list = mapper.getStudent2();
        for (Student stu:list ) {
            System.out.println(stu);
        }
        sqlSession.close();
    }
}

Ⅱ 一對多查詢：老師——學生

在這裡插入圖片描述

（1）實體類

@Data
public class Student {
    private int id;
    private String name;
    private int tid;
}

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

（2）接口

package com.glp.dao;
public interface TeacherMapper {
    Teacher getTeacher(@Param("tid") int id);
    Teacher getTeacher2(@Param("tid") int id);
}

（3）接口對應的Mapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.glp.dao.TeacherMapper">
  <!--方式一          =======================                  -->
    <select id="getTeacher" resultMap="TeacherStudent">
        select s.id sid, s.name sname, t.name tname, t.id tid from
        student s ,teacher t where s.tid = t.id and t.id = #{tid};
    </select>
    <resultMap id="TeacherStudent" type="Teacher">
        <result property="id" column="tid"/>
        <result property="name" column="tname"/>
        <collection property="students" ofType="Student">
            <result property="id" column="sid"/>
            <result property="name" column="sname"/>
            <result property="tid" column="tid"/>
        </collection>
    </resultMap>
    <!--方式二          =======================                  -->
    <select id="getTeacher2" resultMap="TeacherStudent2">
        select * from teacher where id = #{tid};
         <!--這裡的tid和接口中指定的屬性名相同-->
    </select>
    <resultMap id="TeacherStudent2" type="Teacher">
     <result property="id" column="id"/>
        <result property="name" column="name"/>
           <!--上面的兩個可以省略-->
        <collection property="students"  column="id" javaType="ArrayList" ofType="Student"  select="getStuById"/>
    </resultMap>
    <select id="getStuById" resultType="Student">
        select * from student where tid=#{tid};
           <!--查詢老師對應的學生，#{tid}-->
    </select>
</mapper>

方式一：聯表查詢，需要寫復雜SQL

collection 用來處理集合，ofType用來指定集合中的約束類型

聯合查詢時，查詢出所以結果，然後再解析結果中的屬性，將屬性property賦予到collection中。

方式二：子查詢，需要寫復雜映射關系

在這裡插入圖片描述

查詢學生時，需要拿著老師的id去查找，column用來給出老師的id。

（4）測試：

package com.glp.dao;
public class UserDaoTest {
    @Test
    public void getTeacher(){
        SqlSession sqlSession = MyUtils.getSqlSession();
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
        Teacher teacher = mapper.getTeacher(1);
        System.out.println(teacher);
        sqlSession.close();
    }
    @Test
    public void getTeacher2(){
        SqlSession sqlSession = MyUtils.getSqlSession();
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
        Teacher teacher = mapper.getTeacher2(1);
        System.out.println(teacher);
        sqlSession.close();
    }
}

以上為個人經驗，希望能給大傢一個參考，也希望大傢多多支持WalkonNet。

Mybatis 復雜對象resultMap的使用

目錄