mybatis 关联映射

一对一

创建数据表

CREATE TABLE `tb_card` (

`id`  int NOT NULL AUTO_INCREMENT ,

`code`  varchar() NULL ,

PRIMARY KEY (`id`)

);

insert into tb_card(code) values('');

CREATE TABLE tb_person(id int not null PRIMARY KEY auto_increment,name VARCHAR(),sex VARCHAR(),age int,card_id int UNIQUE);

INSERT INTO tb_person(name,sex,age,card_id) VALUES('jack','男',,);

目录结构

Card

package com.example.demo.domain;

import java.io.Serializable;

public class Card implements Serializable {

    private Integer id;

    private String code;

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getCode() {

        return code;

    }

    public void setCode(String code) {

        this.code = code;

    }

}

Person

package com.example.demo.domain;

import java.io.Serializable;

public class Person implements Serializable {

    private Integer id;

    private String name;

    private String sex;

    private Integer age;

    private Card card;

    public Card getCard() {

        return card;

    }

    public void setCard(Card card) {

        this.card = card;

    }

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public String getSex() {

        return sex;

    }

    public void setSex(String sex) {

        this.sex = sex;

    }

    public Integer getAge() {

        return age;

    }

    public void setAge(Integer age) {

        this.age = age;

    }

}

CardMapper

package com.example.demo.mapper;

import com.example.demo.domain.Card;

public interface CardMapper {

    Card selectCardById(Integer id);

}

PersonMapper

package com.example.demo.mapper;

import com.example.demo.domain.Person;

public interface PersonMapper {

    Person selectPersonById(Integer id);

}

CardMapper.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.example.demo.mapper.CardMapper">

    <!--<insert id="save" parameterType="com.example.demo.domain.Card" useGeneratedKeys="true">-->

        <!--INSERT INTO tb_card(code) VALUES (#{code})-->

    <!--</insert>-->

    <select id="selectCardById" parameterType="int" resultType="com.example.demo.domain.Card">

        SELECT  *  FROM tb_card WHERE id=#{id}

    </select>

</mapper>

PersonMapper.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.example.demo.mapper.PersonMapper">

    <!--<insert id="save" parameterType="com.example.demo.domain.Person" useGeneratedKeys="true">-->

        <!--INSERT INTO tb_person(name,sex,age,card_id) VALUES (#{name},#{sex},#{age},#{card_id})-->

    <!--</insert>-->

    <select id="selectPersonById" parameterType="int" resultMap="personMapper">

        SELECT  *  FROM tb_person WHERE id=#{id}

    </select>

    <resultMap id="personMapper" type="com.example.demo.domain.Person">

        <id property="id" column="id"></id>

        <result property="name" column="name"></result>

        <result property="sex" column="sex"></result>

        <result column="age" property="age"></result>

        <association property="card" column="card_id" select="com.example.demo.mapper.CardMapper.selectCardById"

                     javaType="com.example.demo.domain.Card"></association>

    </resultMap>

</mapper>

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>

    <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://192.168.31.146:3306/mydb"/>

                <property name="username" value="root"/>

                <property name="password" value="password"/>

            </dataSource>

        </environment>

    </environments>

    <mappers>

        <mapper resource="CardMapper.xml"></mapper>

        <mapper resource="PersonMapper.xml"></mapper>

    </mappers>

</configuration>

OnoToOneTest

package com.example.demo.test;

import com.example.demo.domain.Person;

import com.example.demo.mapper.PersonMapper;

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.InputStream;

public class OnoToOneTest {

    public static void main(String[] args) throws IOException {

        InputStream inputStream= Resources.getResourceAsStream("mybatis-config.xml");

        SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(inputStream);

        SqlSession session=factory.openSession();

        PersonMapper pm=session.getMapper(PersonMapper.class);

        Person p=pm.selectPersonById();

        System.out.println(p);

        System.out.println(p.getCard());

        session.commit();

        session.close();

    }

}

运行结果：

这里特别需要注意的是CardMapper.xml和PersonMapper.xml的位置。

一对多

Clazz

package com.example.demo.domain;

import java.io.Serializable;

import java.util.List;

public class Clazz implements Serializable {

    private Integer id;

    private String code;

    private String name;

    private List<Student> students;

    public List<Student> getStudents() {

        return students;

    }

    public void setStudents(List<Student> students) {

        this.students = students;

    }

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getCode() {

        return code;

    }

    public void setCode(String code) {

        this.code = code;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

}

Student

package com.example.demo.domain;

import java.io.Serializable;

public class Student implements Serializable {

    private Integer id;

    private String name;

    private String sex;

    private Integer age;

    private Clazz clazz;

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public String getSex() {

        return sex;

    }

    public void setSex(String sex) {

        this.sex = sex;

    }

    public Integer getAge() {

        return age;

    }

    public void setAge(Integer age) {

        this.age = age;

    }

    public Clazz getClazz() {

        return clazz;

    }

    public void setClazz(Clazz clazz) {

        this.clazz = clazz;

    }

}

ClazzMapper.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.example.demo.mapper.ClazzMapper">

    <select id="selectClazzById" parameterType="int"

            resultMap="clazzResultMap">

        SELECT  *  FROM tb_clazz WHERE id=#{id}

    </select>

    <resultMap id="clazzResultMap" type="com.example.demo.domain.Clazz">

        <id column="id" property="id"></id>

        <result property="code" column="code"></result>

        <result column="name" property="name"></result>

        <collection property="students" javaType="ArrayList" column="id" ofType="com.example.demo.domain.Student"

                    select="com.example.demo.mapper.StudentMapper.selectStudentByClazzId" fetchType="lazy">

            <id property="id" column="id"></id>

            <result property="name" column="name"></result>

            <result property="sex" column="sex"></result>

            <result property="age" column="age"></result>

        </collection>

    </resultMap>

</mapper>

StudentMapper.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.example.demo.mapper.StudentMapper">

    <select id="selectStudentById" parameterType="int" resultType="com.example.demo.domain.Student">

        SELECT  *  FROM tb_Student WHERE id=#{id}

    </select>

    <select id="selectStudentByClazzId" parameterType="int" resultType="com.example.demo.domain.Student">

        SELECT * FROM  tb_student WHERE clazz_id=#{id}

    </select>

</mapper>

ClazzMapper

package com.example.demo.mapper;

import com.example.demo.domain.Clazz;

public interface ClazzMapper {

    Clazz selectClazzById(Integer id);

}

StudentMapper

package com.example.demo.mapper;

import com.example.demo.domain.Student;

public interface StudentMapper {

    Student selectStudentByClazzId(Integer id);

}

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>

    <settings>

        <setting name="lazyLoadingEnabled" value="true"/>

        <setting name="aggressiveLazyLoading" value="false"/>

    </settings>

    <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://192.168.31.146:3306/mydb"/>

                <property name="username" value="root"/>

                <property name="password" value="weiwei1207"/>

            </dataSource>

        </environment>

    </environments>

    <mappers>

        <mapper resource="CardMapper.xml"></mapper>

        <mapper resource="PersonMapper.xml"></mapper>

        <mapper resource="ClazzMapper.xml"></mapper>

        <mapper resource="StudentMapper.xml"></mapper>

    </mappers>

</configuration>

注意这里添加了settings配置延迟加载

OneToManyTest

package com.example.demo.test;

import com.example.demo.domain.Clazz;

import com.example.demo.domain.Student;

import com.example.demo.mapper.ClazzMapper;

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.InputStream;

public class OneToManyTest {

    public static void main(String[] args) throws IOException {

        InputStream inputStream= Resources.getResourceAsStream("mybatis-config.xml");

        SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(inputStream);

        SqlSession session=factory.openSession();

        ClazzMapper mapper=session.getMapper(ClazzMapper.class);

        Clazz clazz=mapper.selectClazzById();

        System.out.println(clazz.getId()+" "+clazz.getCode()+" "+clazz.getName());

        for(Student student:clazz.getStudents()){

            System.out.println(student.getId()+" "+student.getName());

        }

    }

}

数据库

运行结果

修改StudentMapper

package com.example.demo.mapper;

import com.example.demo.domain.Student;

public interface StudentMapper {

    Student selectStudentByClazzId(Integer id);

    Student selectStudentById(Integer id);

}

修改StudentMapper.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.example.demo.mapper.StudentMapper">

    <select id="selectStudentById" parameterType="int" resultMap="studentResultMap">

        SELECT  *  FROM tb_student a JOIN tb_clazz b ON a.clazz_id=b.id WHERE a.id=#{id}

    </select>

    <resultMap id="studentResultMap" type="com.example.demo.domain.Student">

        <id property="id" column="id"></id>

        <result property="name" column="name"></result>

        <result property="sex" column="sex"></result>

        <result property="age" column="age"></result>

        <association property="clazz" javaType="com.example.demo.domain.Clazz">

            <id property="id" column="id"></id>

            <result property="code" column="code"></result>

            <result column="name" property="name"></result>

        </association>

    </resultMap>

    <select id="selectStudentByClazzId" parameterType="int" resultType="com.example.demo.domain.Student">

        SELECT * FROM  tb_student WHERE clazz_id=#{id}

    </select>

</mapper>

修改OneToManyTest

StudentMapper mapper=session.getMapper(StudentMapper.class);

        Student student=mapper.selectStudentById();

        System.out.println(student.getId()+" "+student.getName()+" "+student.getClazz().getCode()+" "+student.getClazz().getName());

运行

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mybatis 关联映射

一对一

创建数据表

目录结构

Card

Person

CardMapper

PersonMapper

CardMapper.xml

PersonMapper.xml

mybatis-config.xml

OnoToOneTest

一对多

Clazz

Student

ClazzMapper.xml

StudentMapper.xml

ClazzMapper

StudentMapper

mybatis-config.xml

OneToManyTest

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