MyBatis一對(duì)多和多對(duì)一

在學(xué)習(xí)MyBatis3的過程中，文檔上面一直在強(qiáng)調(diào)一個(gè)id的東西！在做這個(gè)實(shí)驗(yàn)的時(shí)候，也因?yàn)闆]有理解清楚id含義而導(dǎo)致一對(duì)多的“多”中也只有一條數(shù)據(jù)。id和result的唯一不同是id表示的結(jié)果將是當(dāng)比較對(duì)象實(shí)例時(shí)用到的標(biāo)識(shí)屬性。這幫助來改進(jìn)整體表現(xiàn)，特別是緩存和嵌入結(jié)果映射。所以不同數(shù)據(jù)的id應(yīng)該唯一區(qū)別，不然導(dǎo)致數(shù)據(jù)**結(jié)果集只有一條數(shù)據(jù)。
一、表

order.jpg

person.jpg

二、實(shí)體
1.person

[java] view plain copy

package com.kerwin.mybatis.pojo;

import java.util.List;

public class Person {

private int id;  
private String name;  
private List<Orders> orderList;  

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 List<Orders> getOrderList() {  
    return orderList;  
}  

public void setOrderList(List<Orders> orderList) {  
    this.orderList = orderList;  
}  

@Override  
public String toString() {  
    return "Person [id=" + id + ", name=" + name + "]";  
}  

public Person() {  
    super();  
    // TODO Auto-generated constructor stub  
}  

public Person(int id, String name, List<Orders> orderList) {  
    super();  
    this.id = id;  
    this.name = name;  
    this.orderList = orderList;  
}

}

[java] view plain copy

package com.kerwin.mybatis.pojo;

import java.util.List;

public class Person {

private int id;  
private String name;  
private List<Orders> orderList;  

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 List<Orders> getOrderList() {  
    return orderList;  
}  

public void setOrderList(List<Orders> orderList) {  
    this.orderList = orderList;  
}  

@Override  
public String toString() {  
    return "Person [id=" + id + ", name=" + name + "]";  
}  

public Person() {  
    super();  
    // TODO Auto-generated constructor stub  
}  

public Person(int id, String name, List<Orders> orderList) {  
    super();  
    this.id = id;  
    this.name = name;  
    this.orderList = orderList;  
}

}

2.order

[java] view plain copy

package com.kerwin.mybatis.pojo;

public class Orders {
private int id;
private double price;
private Person person;

public Person getPerson() {  
    return person;  
}  

public void setPerson(Person person) {  
    this.person = person;  
}  

public int getId() {  
    return id;  
}  

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



public double getPrice() {  
    return price;  
}  

public void setPrice(double price) {  
    this.price = price;  
}  


  

@Override  
public String toString() {  
    return "Orders [id=" + id + ", price=" + price + "]";  
}  

public Orders() {  
    super();  
    // TODO Auto-generated constructor stub  
}

}

[java] view plain copy

package com.kerwin.mybatis.pojo;

public class Orders {
private int id;
private double price;
private Person person;

public Person getPerson() {  
    return person;  
}  

public void setPerson(Person person) {  
    this.person = person;  
}  

public int getId() {  
    return id;  
}  

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



public double getPrice() {  
    return price;  
}  

public void setPrice(double price) {  
    this.price = price;  
}  


  

@Override  
public String toString() {  
    return "Orders [id=" + id + ", price=" + price + "]";  
}  

public Orders() {  
    super();  
    // TODO Auto-generated constructor stub  
}

}

三、映射mapper文件
1. PersonMapper.xml

[html] view plain copy

<?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.kerwin.mybatis.pojo.Person">
<resultMap type="com.kerwin.mybatis.pojo.Person" id="personreSultMap">
<id column="p_id" property="id"/>
<result column="name" property="name"/>
<collection property="orderList" ofType="com.kerwin.mybatis.pojo.Orders" column="pid">
<id column="o_id" property="id"/>
<result column="price" property="price"/>
</collection>

</resultMap>  
  
<select id="selectPersonFetchOrder" parameterType="int" resultMap="personreSultMap" >  
    select p.*,o.* from person p,orders o where o.pid=p.p_id and p.p_id=#{id}  
</select>

</mapper>

[html] view plain copy

<?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.kerwin.mybatis.pojo.Person">
<resultMap type="com.kerwin.mybatis.pojo.Person" id="personreSultMap">
<id column="p_id" property="id"/>
<result column="name" property="name"/>
<collection property="orderList" ofType="com.kerwin.mybatis.pojo.Orders" column="pid">
<id column="o_id" property="id"/>
<result column="price" property="price"/>
</collection>

</resultMap>  
  
<select id="selectPersonFetchOrder" parameterType="int" resultMap="personreSultMap" >  
    select p.*,o.* from person p,orders o where o.pid=p.p_id and p.p_id=#{id}  
</select>

</mapper>

2. OrdersMapper.xml

[html] view plain copy

<?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.kerwin.mybatis.pojo.Orders">
<resultMap type="com.kerwin.mybatis.pojo.Orders" id="OrdersResultMap">
<id column="o_id" property="id"/>
<result column="price" property="price"/>
<association property="person" javaType="com.kerwin.mybatis.pojo.Person">
<id column="p_id" property="id"/>
<result column="name" property="name"/>
</association>
</resultMap>

<select id="selectOrdersFetchPerson" resultMap="OrdersResultMap">  
    select p.*,o.* from person p,orders o where o.pid=p.p_id and o.o_id=#{id}   
</select>

</mapper>

[html] view plain copy

<?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.kerwin.mybatis.pojo.Orders">
<resultMap type="com.kerwin.mybatis.pojo.Orders" id="OrdersResultMap">
<id column="o_id" property="id"/>
<result column="price" property="price"/>
<association property="person" javaType="com.kerwin.mybatis.pojo.Person">
<id column="p_id" property="id"/>
<result column="name" property="name"/>
</association>
</resultMap>

<select id="selectOrdersFetchPerson" resultMap="OrdersResultMap">  
    select p.*,o.* from person p,orders o where o.pid=p.p_id and o.o_id=#{id}   
</select>

</mapper>

3.sqlMapConfig.xml

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<?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>
<typeAlias type="com.kerwin.mybatis.pojo.Author" alias="Author"/>
</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://localhost:3306/mybatis"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/kerwin/mybatis/pojo/AuthorMapper.xml"/>
<mapper resource="com/kerwin/mybatis/pojo/PostMapper.xml"/>
<mapper resource="com/kerwin/mybatis/pojo/PersonMapper.xml"/>
<mapper resource="com/kerwin/mybatis/pojo/OrdersMapper.xml"/>
</mappers>
</configuration>

[html] view plain copy

<?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>
<typeAlias type="com.kerwin.mybatis.pojo.Author" alias="Author"/>
</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://localhost:3306/mybatis"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/kerwin/mybatis/pojo/AuthorMapper.xml"/>
<mapper resource="com/kerwin/mybatis/pojo/PostMapper.xml"/>
<mapper resource="com/kerwin/mybatis/pojo/PersonMapper.xml"/>
<mapper resource="com/kerwin/mybatis/pojo/OrdersMapper.xml"/>
</mappers>
</configuration>

四。測試類

[java] view plain copy

/**

*/
package com.kerwin.mybatis.test;

import java.io.InputStream;

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 org.junit.BeforeClass;
import org.junit.Test;

import com.kerwin.mybatis.pojo.Orders;
import com.kerwin.mybatis.pojo.Person;

/**

  • @author Administrator

*/
public class PersonAndOrderTest {

private static SqlSessionFactory sessionFactory;  
  
/** 
 * @throws java.lang.Exception 
 */  
@BeforeClass  
public static void setUpBeforeClass() throws Exception {  
    SqlSessionFactoryBuilder factoryBuilder = new SqlSessionFactoryBuilder();  
    InputStream inputStream = Resources.getResourceAsStream("sqlMapConfig.xml");  
    sessionFactory = factoryBuilder.build(inputStream);  

}  
  
//一對(duì)多，查詢person（一）級(jí)聯(lián)查詢訂單order（多）  
@Test  
public void testSelectPersonFetchOrder() throws Exception {  
    SqlSession session = sessionFactory.openSession();  
    Person person = session.selectOne("com.kerwin.mybatis.pojo.Person.selectPersonFetchOrder", 1);  
    System.out.println(person);  
    System.out.println(person.getOrderList().size());  
    for(Orders orders : person.getOrderList()){  
        System.out.println(orders);  
    }  
    session.close();  
}  
  
//多對(duì)一，查詢訂單order（多）級(jí)聯(lián)查詢person（一）  
@Test  
public void testSelectOrdersFetchPerson() throws Exception{  
    SqlSession session = sessionFactory.openSession();  
    Orders orders = session.selectOne("com.kerwin.mybatis.pojo.Orders.selectOrdersFetchPerson", 1);  
    System.out.println(orders);  
    System.out.println(orders.getPerson());  
    session.close();  
}

}

[java] view plain copy

/**

*/
package com.kerwin.mybatis.test;

import java.io.InputStream;

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 org.junit.BeforeClass;
import org.junit.Test;

import com.kerwin.mybatis.pojo.Orders;
import com.kerwin.mybatis.pojo.Person;

/**

  • @author Administrator

*/
public class PersonAndOrderTest {

private static SqlSessionFactory sessionFactory;  
  
/** 
 * @throws java.lang.Exception 
 */  
@BeforeClass  
public static void setUpBeforeClass() throws Exception {  
    SqlSessionFactoryBuilder factoryBuilder = new SqlSessionFactoryBuilder();  
    InputStream inputStream = Resources.getResourceAsStream("sqlMapConfig.xml");  
    sessionFactory = factoryBuilder.build(inputStream);  

}  
  
//一對(duì)多，查詢person（一）級(jí)聯(lián)查詢訂單order（多）  
@Test  
public void testSelectPersonFetchOrder() throws Exception {  
    SqlSession session = sessionFactory.openSession();  
    Person person = session.selectOne("com.kerwin.mybatis.pojo.Person.selectPersonFetchOrder", 1);  
    System.out.println(person);  
    System.out.println(person.getOrderList().size());  
    for(Orders orders : person.getOrderList()){  
        System.out.println(orders);  
    }  
    session.close();  
}  
  
//多對(duì)一，查詢訂單order（多）級(jí)聯(lián)查詢person（一）  
@Test  
public void testSelectOrdersFetchPerson() throws Exception{  
    SqlSession session = sessionFactory.openSession();  
    Orders orders = session.selectOne("com.kerwin.mybatis.pojo.Orders.selectOrdersFetchPerson", 1);  
    System.out.println(orders);  
    System.out.println(orders.getPerson());  
    session.close();  
}

}

五、測試結(jié)果
1.一對(duì)多，查詢person（一）級(jí)聯(lián)查詢訂單order（多）

一對(duì)多.jpg

**

2.多對(duì)一，查詢訂單order（多）級(jí)聯(lián)查詢person（一）
**

多對(duì)一.jpg

**

注意：兩張表中的主鍵id字段名要唯一，例如不能都寫id，不然的話，在一對(duì)多查詢的時(shí)候就會(huì)出現(xiàn)：級(jí)聯(lián)出來的訂單項(xiàng)只有一條記錄。我之前就是將兩張表的主鍵id字段名都寫為id，導(dǎo)致測試結(jié)果級(jí)聯(lián)出來的多一直只有一條數(shù)據(jù)，具體如下：
**

ps.jpg

**

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