【Mybatis】一对一实例

①创建数据库和表，数据库为mytest，表为father和child

 DROP TABLE IF EXISTS child;
 DROP TABLE IF EXISTS father;

 CREATE TABLE child(
     child_id INT PRIMARY KEY auto_increment NOT NULL,
     child_name VARCHAR(20)
 );

 CREATE TABLE father(
     father_id INT PRIMARY KEY auto_increment NOT NULL,
     father_name VARCHAR(20),
     child_id INT
 );

 ALTER TABLE father ADD CONSTRAINT fk_child_id FOREIGN KEY (child_id) REFERENCES child(child_id);

 INSERT INTO child(child_name) VALUES ("Guo Xiang");
 INSERT INTO child(child_name) VALUES ("Zhang Wuji");
 INSERT INTO father(father_name, child_id) VALUES ("Guo Jing", 1);
 INSERT INTO father(father_name, child_id) VALUES ("Zhang Cuishan", 2);

father&child

②创建Java工程，导入相应的jar包

③创建配置文件conf.xml和数据库配置文件db.properties

 <?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"></properties>
     <environments default="development">
         <environment id="development">
             <transactionManager type="JDBC"></transactionManager>
             <dataSource type="POOLED">
                 <property name="driver" value="${driver}"/>
                 <property name="url" value="${url}"/>
                 <property name="username" value="${name}"/>
                 <property name="password" value="${password}"/>
             </dataSource>
         </environment>
     </environments>

     <mappers>
         <mapper resource="org/mybatis/mapping/fatherMapper.xml"/>
     </mappers>
 </configuration>

conf.xml

 driver = com.mysql.jdbc.Driver
 url = jdbc:mysql://localhost:3306/mytest
 name = root
 password = root

db.properties

④创建实体类Father和Child

 package org.mybatis.domain;

 public class Child {

     private int child_id;
     private String child_name;

     public int getChild_id() {
         return child_id;
     }
     public void setChild_id(int child_id) {
         this.child_id = child_id;
     }
     public String getChild_name() {
         return child_name;
     }
     public void setChild_name(String child_name) {
         this.child_name = child_name;
     }

     @Override
     public String toString() {
         return "[Child = child_id:" + child_id + ", child_name:" + child_name + "]";
     }

 }

Child

 package org.mybatis.domain;

 public class Father {

     private int father_id;
     private String father_name;
     private Child child;

     public int getFather_id() {
         return father_id;
     }
     public void setFather_id(int father_id) {
         this.father_id = father_id;
     }
     public String getFather_name() {
         return father_name;
     }
     public void setFather_name(String father_name) {
         this.father_name = father_name;
     }

     public Child getChild() {
         return child;
     }
     public void setChild(Child child) {
         this.child = child;
     }
     @Override
     public String toString() {
         return "[Father = father_id:" + father_id + ", father_name:" + father_name
                 + ", child:" + child + "]";
     }

 }

Father

⑤创建sql映射文件fatherMapper.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="org.mybatis.mapping.fatherMapper">

     <!-- 方式一：嵌套结果 -->
 <!--     <select id="getChild" parameterType="int" resultMap="ChildMap"> -->
 <!--         select * from child c, father f where c.child_id = f.child_id and f.father_id=#{id} -->
 <!--     </select> -->

 <!--     <resultMap type="org.mybatis.domain.Father" id="ChildMap"> -->
 <!--         <id property="father_id" column="father_id"/> -->
 <!--         <result property="father_name" column="father_name" /> -->
 <!--         <association property="child" javaType="org.mybatis.domain.Child"> -->
 <!--             <id property="child_id" column="child_id"/> -->
 <!--             <result property="child_name" column="child_name"/> -->
 <!--         </association> -->
 <!--     </resultMap> -->

     <!-- 方式二：嵌套查询 -->
     <select id="getChild" parameterType="int" resultMap="ChildMap">
         select * from father where father_id=#{id}
     </select>

     <resultMap type="org.mybatis.domain.Father" id="ChildMap">
         <id property="father_id" column="father_id"/>
         <result property="father_name" column="father_name" />
         <collection property="child" column="child_id" select="getChildCollection">
         </collection>
     </resultMap>

     <select id="getChildCollection" resultType="org.mybatis.domain.Child">
         select * from child where child_id=#{child_id}
     </select>

 </mapper>

fatherMapper.xml

⑥向配置文件中注册 fatherMapper.xml 文件【已添加，查看第③步】

⑦测试类

 package org.mybatis.app;

 import java.io.InputStream;

 import org.apache.ibatis.session.SqlSession;
 import org.apache.ibatis.session.SqlSessionFactory;
 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 import org.junit.Before;
 import org.junit.Test;
 import org.mybatis.domain.Father;

 public class TestOneToOne {

     SqlSession session;

     @Before
     public void beforeLoad() {
         InputStream inputStream =
                 TestOneToOne.class.getClassLoader().getResourceAsStream("conf.xml");
         SqlSessionFactory sqlSessionFactory =
                 new SqlSessionFactoryBuilder().build(inputStream);
         session = sqlSessionFactory.openSession();
     }

     @Test
     public void testOneToOne() {
         // 根据fatherID得到child
         String statement = "org.mybatis.mapping.fatherMapper.getChild";
         Father father = session.selectOne(statement,2);
         session.close();
         System.out.println(father.getFather_name() + "'s child is "
                 + father.getChild().getChild_name());
     }
 }

TestOneToOne

⑧结构图

fatherMapper.xml中有两种方式，两种方式的结果一样