MyBatis一对多和多对一

     在学习MyBatis3的过程中，文档上面一直在强调一个id的东西！在做这个实验的时候，也因为没有理解清楚id含义而导致 一对多的“多”中也只有一条数据。id和result的唯一不同是id表示的结果将是当比较对象实例时用到的标识属性。这帮助来改进整体表现，特别是缓存和嵌入结果映射。 所以不同数据的id应该唯一区别，不然导致数据 结果集只有一条数据。

一、表

二、实体

1.person

[java] view plain copy

print ?

1. package com.kerwin.mybatis.pojo;  
2.   
3. import java.util.List;  
4.   
5. public class Person {  
6.   
7.     private int id;  
8.     private String name;  
9.     private List<Orders> orderList;  
10.   
11.     public int getId() {  
12.         return id;  
13.     }  
14.   
15.     public void setId(int id) {  
16.         this.id = id;  
17.     }  
18.   
19.     public String getName() {  
20.         return name;  
21.     }  
22.   
23.     public void setName(String name) {  
24.         this.name = name;  
25.     }  
26.   
27.     public List<Orders> getOrderList() {  
28.         return orderList;  
29.     }  
30.   
31.     public void setOrderList(List<Orders> orderList) {  
32.         this.orderList = orderList;  
33.     }  
34.   
35.     @Override  
36.     public String toString() {  
37.         return “Person [id=” + id + “, name=” + name + “]”;  
38.     }  
39.   
40.     public Person() {  
41.         super();  
42.         // TODO Auto-generated constructor stub  
43.     }  
44.   
45.     public Person(int id, String name, List<Orders> orderList) {  
46.         super();  
47.         this.id = id;  
48.         this.name = name;  
49.         this.orderList = orderList;  
50.     }  
51.   
52. }  

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

print ?

1. package com.kerwin.mybatis.pojo;  
2.   
3. public class Orders {  
4.     private int id;  
5.     private double price;  
6.     private Person person;  
7.       
8.       
9.       
10.     public Person getPerson() {  
11.         return person;  
12.     }  
13.   
14.     public void setPerson(Person person) {  
15.         this.person = person;  
16.     }  
17.   
18.     public int getId() {  
19.         return id;  
20.     }  
21.   
22.     public void setId(int id) {  
23.         this.id = id;  
24.     }  
25.   
26.   
27.   
28.     public double getPrice() {  
29.         return price;  
30.     }  
31.   
32.     public void setPrice(double price) {  
33.         this.price = price;  
34.     }  
35.   
36.   
37.       
38.   
39.     @Override  
40.     public String toString() {  
41.         return “Orders [id=” + id + “, price=” + price + “]”;  
42.     }  
43.   
44.     public Orders() {  
45.         super();  
46.         // TODO Auto-generated constructor stub  
47.     }  
48.   
49. }  

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

print ?

1. <?xml version=“1.0” encoding=“UTF-8”?>  
2. <!DOCTYPE mapper  
3.   PUBLIC ”-//mybatis.org//DTD Mapper 3.0//EN”  
4.   “http://mybatis.org/dtd/mybatis-3-mapper.dtd”>  
5.       
6. <mapper namespace=“com.kerwin.mybatis.pojo.Person”>  
7.     <resultMap type=“com.kerwin.mybatis.pojo.Person” id=“personreSultMap”>  
8.         <id column=“p_id” property=“id”/>  
9.         <result column=“name” property=“name”/>  
10.         <collection property=“orderList” ofType=“com.kerwin.mybatis.pojo.Orders” column=“pid”>  
11.             <id column=“o_id” property=“id”/>  
12.             <result column=“price” property=“price”/>  
13.         </collection>  
14.           
15.     </resultMap>  
16.       
17.     <select id=“selectPersonFetchOrder” parameterType=“int” resultMap=“personreSultMap” >  
18.         select p.*,o.* from person p,orders o where o.pid=p.p_id and p.p_id=#{id}  
19.     </select>  
20.       
21.       
22. </mapper>  

<?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

print ?

1. <?xml version=“1.0” encoding=“UTF-8”?>  
2. <!DOCTYPE mapper  
3.   PUBLIC ”-//mybatis.org//DTD Mapper 3.0//EN”  
4.   “http://mybatis.org/dtd/mybatis-3-mapper.dtd”>  
5.   
6. <mapper namespace=“com.kerwin.mybatis.pojo.Orders”>  
7.     <resultMap type=“com.kerwin.mybatis.pojo.Orders” id=“OrdersResultMap”>  
8.         <id column=“o_id” property=“id”/>  
9.         <result column=“price” property=“price”/>  
10.         <association property=“person” javaType=“com.kerwin.mybatis.pojo.Person”>  
11.             <id column=“p_id” property=“id”/>  
12.             <result column=“name” property=“name”/>  
13.         </association>  
14.     </resultMap>  
15.       
16.     <select id=“selectOrdersFetchPerson” resultMap=“OrdersResultMap”>  
17.         select p.*,o.* from person p,orders o where o.pid=p.p_id and o.o_id=#{id}   
18.     </select>  
19.   
20. </mapper>  

<?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

[html] view plain copy

print ?

1. <?xml version=“1.0” encoding=“UTF-8” ?>  
2. <!DOCTYPE configuration  
3.   PUBLIC ”-//mybatis.org//DTD Config 3.0//EN”  
4.   “http://mybatis.org/dtd/mybatis-3-config.dtd”>  
5. <configuration>  
6.   
7. <typeAliases>  
8.     <typeAlias type=“com.kerwin.mybatis.pojo.Author” alias=“Author”/>  
9. </typeAliases>  
10.   <environments default=“development”>  
11.     <environment id=“development”>  
12.       <transactionManager type=“JDBC”/>  
13.       <dataSource type=“POOLED”>  
14.         <property name=“driver” value=“com.mysql.jdbc.Driver”/>  
15.         <property name=“url” value=“jdbc:mysql://localhost:3306/mybatis”/>  
16.         <property name=“username” value=“root”/>  
17.         <property name=“password” value=“root”/>  
18.       </dataSource>  
19.     </environment>  
20.   </environments>  
21.   <mappers>  
22.     <mapper resource=“com/kerwin/mybatis/pojo/AuthorMapper.xml”/>  
23.     <mapper resource=“com/kerwin/mybatis/pojo/PostMapper.xml”/>  
24.     <mapper resource=“com/kerwin/mybatis/pojo/PersonMapper.xml”/>  
25.     <mapper resource=“com/kerwin/mybatis/pojo/OrdersMapper.xml”/>  
26.   </mappers>  
27. </configuration>  

<?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。测试类

[java] view plain copy

print ?

1. /** 
2.  *  
3.  */  
4. package com.kerwin.mybatis.test;  
5.   
6. import java.io.InputStream;  
7.   
8. import org.apache.ibatis.io.Resources;  
9. import org.apache.ibatis.session.SqlSession;  
10. import org.apache.ibatis.session.SqlSessionFactory;  
11. import org.apache.ibatis.session.SqlSessionFactoryBuilder;  
12. import org.junit.BeforeClass;  
13. import org.junit.Test;  
14.   
15. import com.kerwin.mybatis.pojo.Orders;  
16. import com.kerwin.mybatis.pojo.Person;  
17.   
18. /** 
19.  * @author Administrator 
20.  *  
21.  */  
22. public class PersonAndOrderTest {  
23.   
24.     private static SqlSessionFactory sessionFactory;  
25.       
26.     /** 
27.      * @throws java.lang.Exception 
28.      */  
29.     @BeforeClass  
30.     public static void setUpBeforeClass() throws Exception {  
31.         SqlSessionFactoryBuilder factoryBuilder = new SqlSessionFactoryBuilder();  
32.         InputStream inputStream = Resources.getResourceAsStream(”sqlMapConfig.xml”);  
33.         sessionFactory = factoryBuilder.build(inputStream);  
34.   
35.     }  
36.       
37.     //一对多，查询person（一）级联查询订单order（多）  
38.     @Test  
39.     public void testSelectPersonFetchOrder() throws Exception {  
40.         SqlSession session = sessionFactory.openSession();  
41.         Person person = session.selectOne(”com.kerwin.mybatis.pojo.Person.selectPersonFetchOrder”, 1);  
42.         System.out.println(person);  
43.         System.out.println(person.getOrderList().size());  
44.         for(Orders orders : person.getOrderList()){  
45.             System.out.println(orders);  
46.         }  
47.         session.close();  
48.     }  
49.       
50.     //多对一，查询订单order（多）级联查询person（一）  
51.     @Test  
52.     public void testSelectOrdersFetchPerson() throws Exception{  
53.         SqlSession session = sessionFactory.openSession();  
54.         Orders orders = session.selectOne(”com.kerwin.mybatis.pojo.Orders.selectOrdersFetchPerson”, 1);  
55.         System.out.println(orders);  
56.         System.out.println(orders.getPerson());  
57.         session.close();  
58.     }  
59.       
60. }  

/**
 * 
 */
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);

    }

    //一对多，查询person（一）级联查询订单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();
    }

    //多对一，查询订单order（多）级联查询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、测试结果

1.一对多，查询person（一）级联查询订单order（多）

2.多对一，查询订单order（多）级联查询person（一）

注意：两张表中的主键id字段名要唯一，例如不能都写id，不然的话，在一对多查询的时候就会出现：级联出来的订单项只有一条记录。我之前就是将两张表的主键id字段名都写为id，导致测试结果级联出来的多一直只有一条数据，具体如下：

                </div>

     在学习MyBatis3的过程中，文档上面一直在强调一个id的东西！在做这个实验的时候，也因为没有理解清楚id含义而导致 一对多的“多”中也只有一条数据。id和result的唯一不同是id表示的结果将是当比较对象实例时用到的标识属性。这帮助来改进整体表现，特别是缓存和嵌入结果映射。 所以不同数据的id应该唯一区别，不然导致数据 结果集只有一条数据。

一、表

二、实体

1.person

[java] view plain copy

print ?

1. package com.kerwin.mybatis.pojo;  
2.   
3. import java.util.List;  
4.   
5. public class Person {  
6.   
7.     private int id;  
8.     private String name;  
9.     private List<Orders> orderList;  
10.   
11.     public int getId() {  
12.         return id;  
13.     }  
14.   
15.     public void setId(int id) {  
16.         this.id = id;  
17.     }  
18.   
19.     public String getName() {  
20.         return name;  
21.     }  
22.   
23.     public void setName(String name) {  
24.         this.name = name;  
25.     }  
26.   
27.     public List<Orders> getOrderList() {  
28.         return orderList;  
29.     }  
30.   
31.     public void setOrderList(List<Orders> orderList) {  
32.         this.orderList = orderList;  
33.     }  
34.   
35.     @Override  
36.     public String toString() {  
37.         return “Person [id=” + id + “, name=” + name + “]”;  
38.     }  
39.   
40.     public Person() {  
41.         super();  
42.         // TODO Auto-generated constructor stub  
43.     }  
44.   
45.     public Person(int id, String name, List<Orders> orderList) {  
46.         super();  
47.         this.id = id;  
48.         this.name = name;  
49.         this.orderList = orderList;  
50.     }  
51.   
52. }  

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

print ?

1. package com.kerwin.mybatis.pojo;  
2.   
3. public class Orders {  
4.     private int id;  
5.     private double price;  
6.     private Person person;  
7.       
8.       
9.       
10.     public Person getPerson() {  
11.         return person;  
12.     }  
13.   
14.     public void setPerson(Person person) {  
15.         this.person = person;  
16.     }  
17.   
18.     public int getId() {  
19.         return id;  
20.     }  
21.   
22.     public void setId(int id) {  
23.         this.id = id;  
24.     }  
25.   
26.   
27.   
28.     public double getPrice() {  
29.         return price;  
30.     }  
31.   
32.     public void setPrice(double price) {  
33.         this.price = price;  
34.     }  
35.   
36.   
37.       
38.   
39.     @Override  
40.     public String toString() {  
41.         return “Orders [id=” + id + “, price=” + price + “]”;  
42.     }  
43.   
44.     public Orders() {  
45.         super();  
46.         // TODO Auto-generated constructor stub  
47.     }  
48.   
49. }  

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

print ?

1. <?xml version=“1.0” encoding=“UTF-8”?>  
2. <!DOCTYPE mapper  
3.   PUBLIC ”-//mybatis.org//DTD Mapper 3.0//EN”  
4.   “http://mybatis.org/dtd/mybatis-3-mapper.dtd”>  
5.       
6. <mapper namespace=“com.kerwin.mybatis.pojo.Person”>  
7.     <resultMap type=“com.kerwin.mybatis.pojo.Person” id=“personreSultMap”>  
8.         <id column=“p_id” property=“id”/>  
9.         <result column=“name” property=“name”/>  
10.         <collection property=“orderList” ofType=“com.kerwin.mybatis.pojo.Orders” column=“pid”>  
11.             <id column=“o_id” property=“id”/>  
12.             <result column=“price” property=“price”/>  
13.         </collection>  
14.           
15.     </resultMap>  
16.       
17.     <select id=“selectPersonFetchOrder” parameterType=“int” resultMap=“personreSultMap” >  
18.         select p.*,o.* from person p,orders o where o.pid=p.p_id and p.p_id=#{id}  
19.     </select>  
20.       
21.       
22. </mapper>  

<?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

print ?

1. <?xml version=“1.0” encoding=“UTF-8”?>  
2. <!DOCTYPE mapper  
3.   PUBLIC ”-//mybatis.org//DTD Mapper 3.0//EN”  
4.   “http://mybatis.org/dtd/mybatis-3-mapper.dtd”>  
5.   
6. <mapper namespace=“com.kerwin.mybatis.pojo.Orders”>  
7.     <resultMap type=“com.kerwin.mybatis.pojo.Orders” id=“OrdersResultMap”>  
8.         <id column=“o_id” property=“id”/>  
9.         <result column=“price” property=“price”/>  
10.         <association property=“person” javaType=“com.kerwin.mybatis.pojo.Person”>  
11.             <id column=“p_id” property=“id”/>  
12.             <result column=“name” property=“name”/>  
13.         </association>  
14.     </resultMap>  
15.       
16.     <select id=“selectOrdersFetchPerson” resultMap=“OrdersResultMap”>  
17.         select p.*,o.* from person p,orders o where o.pid=p.p_id and o.o_id=#{id}   
18.     </select>  
19.   
20. </mapper>  

<?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

[html] view plain copy

print ?

1. <?xml version=“1.0” encoding=“UTF-8” ?>  
2. <!DOCTYPE configuration  
3.   PUBLIC ”-//mybatis.org//DTD Config 3.0//EN”  
4.   “http://mybatis.org/dtd/mybatis-3-config.dtd”>  
5. <configuration>  
6.   
7. <typeAliases>  
8.     <typeAlias type=“com.kerwin.mybatis.pojo.Author” alias=“Author”/>  
9. </typeAliases>  
10.   <environments default=“development”>  
11.     <environment id=“development”>  
12.       <transactionManager type=“JDBC”/>  
13.       <dataSource type=“POOLED”>  
14.         <property name=“driver” value=“com.mysql.jdbc.Driver”/>  
15.         <property name=“url” value=“jdbc:mysql://localhost:3306/mybatis”/>  
16.         <property name=“username” value=“root”/>  
17.         <property name=“password” value=“root”/>  
18.       </dataSource>  
19.     </environment>  
20.   </environments>  
21.   <mappers>  
22.     <mapper resource=“com/kerwin/mybatis/pojo/AuthorMapper.xml”/>  
23.     <mapper resource=“com/kerwin/mybatis/pojo/PostMapper.xml”/>  
24.     <mapper resource=“com/kerwin/mybatis/pojo/PersonMapper.xml”/>  
25.     <mapper resource=“com/kerwin/mybatis/pojo/OrdersMapper.xml”/>  
26.   </mappers>  
27. </configuration>  

<?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。测试类

[java] view plain copy

print ?

1. /** 
2.  *  
3.  */  
4. package com.kerwin.mybatis.test;  
5.   
6. import java.io.InputStream;  
7.   
8. import org.apache.ibatis.io.Resources;  
9. import org.apache.ibatis.session.SqlSession;  
10. import org.apache.ibatis.session.SqlSessionFactory;  
11. import org.apache.ibatis.session.SqlSessionFactoryBuilder;  
12. import org.junit.BeforeClass;  
13. import org.junit.Test;  
14.   
15. import com.kerwin.mybatis.pojo.Orders;  
16. import com.kerwin.mybatis.pojo.Person;  
17.   
18. /** 
19.  * @author Administrator 
20.  *  
21.  */  
22. public class PersonAndOrderTest {  
23.   
24.     private static SqlSessionFactory sessionFactory;  
25.       
26.     /** 
27.      * @throws java.lang.Exception 
28.      */  
29.     @BeforeClass  
30.     public static void setUpBeforeClass() throws Exception {  
31.         SqlSessionFactoryBuilder factoryBuilder = new SqlSessionFactoryBuilder();  
32.         InputStream inputStream = Resources.getResourceAsStream(”sqlMapConfig.xml”);  
33.         sessionFactory = factoryBuilder.build(inputStream);  
34.   
35.     }  
36.       
37.     //一对多，查询person（一）级联查询订单order（多）  
38.     @Test  
39.     public void testSelectPersonFetchOrder() throws Exception {  
40.         SqlSession session = sessionFactory.openSession();  
41.         Person person = session.selectOne(”com.kerwin.mybatis.pojo.Person.selectPersonFetchOrder”, 1);  
42.         System.out.println(person);  
43.         System.out.println(person.getOrderList().size());  
44.         for(Orders orders : person.getOrderList()){  
45.             System.out.println(orders);  
46.         }  
47.         session.close();  
48.     }  
49.       
50.     //多对一，查询订单order（多）级联查询person（一）  
51.     @Test  
52.     public void testSelectOrdersFetchPerson() throws Exception{  
53.         SqlSession session = sessionFactory.openSession();  
54.         Orders orders = session.selectOne(”com.kerwin.mybatis.pojo.Orders.selectOrdersFetchPerson”, 1);  
55.         System.out.println(orders);  
56.         System.out.println(orders.getPerson());  
57.         session.close();  
58.     }  
59.       
60. }  

/**
 * 
 */
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);

    }

    //一对多，查询person（一）级联查询订单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();
    }

    //多对一，查询订单order（多）级联查询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、测试结果

1.一对多，查询person（一）级联查询订单order（多）

2.多对一，查询订单order（多）级联查询person（一）

注意：两张表中的主键id字段名要唯一，例如不能都写id，不然的话，在一对多查询的时候就会出现：级联出来的订单项只有一条记录。我之前就是将两张表的主键id字段名都写为id，导致测试结果级联出来的多一直只有一条数据，具体如下：

                </div>