多对一 一对多 多对多
一.准备测试环境（创建数据库表）
1>.创建customers表；
use yinzhengjie; create table if not exists customers(id int primary key auto_increment,name varchar(20) , age int) ;
2>.创建orders表
use yinzhengjie; create table orders(id int primary key auto_increment , orderno varchar(20) , price float , cid int) ;
3>.创建指定的包名和文件，具体结构如下：
4>.添加Maven依赖
1 <?xml version="1.0" encoding="UTF-8"?> 2 <project xmlns="http://maven.apache.org/POM/4.0.0" 3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 4 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> 5 <modelVersion>4.0.0</modelVersion> 6 <groupId>cn.org.yinzhengjie</groupId> 7 <artifactId>Mybatis</artifactId> 8 <version>1.0-SNAPSHOT</version> 9 <dependencies> 10 <dependency> 11 <groupId>junit</groupId> 12 <artifactId>junit</artifactId> 13 <version>4.11</version> 14 </dependency> 15 <dependency> 16 <groupId>mysql</groupId> 17 <artifactId>mysql-connector-java</artifactId> 18 <version>5.1.17</version> 19 </dependency> 20 <dependency> 21 <groupId>org.mybatis</groupId> 22 <artifactId>mybatis</artifactId> 23 <version>3.2.1</version> 24 </dependency> 25 </dependencies> 26 </project>
二.编写自定义类
1>.编写Customer类
1 /*
2 @author :yinzhengjie
3 Blog:http://www.cnblogs.com/yinzhengjie/tag/Java%E5%9F%BA%E7%A1%80/
4 EMAIL:y1053419035@qq.com
5 */
6 package cn.org.yinzhengjie.mybatis.domain.one2many;
7
8 import java.util.ArrayList;
9 import java.util.List;
10
11 /**
12 * 客户
13 */
14 public class Customer {
15 private Integer id ;
16 private String name ;
17 private int age ;
18
19 //建立从Customer到Order之间一对多关系,因为一个客户可能会有多个订单。我们将多个订单放在一个list中。
20 private List<Order> orders = new ArrayList<Order>() ;
21
22 public List<Order> getOrders() {
23 return orders;
24 }
25
26 public void setOrders(List<Order> orders) {
27 this.orders = orders;
28 }
29
30 public Integer getId() {
31 return id;
32 }
33
34 public void setId(Integer id) {
35 this.id = id;
36 }
37
38 public String getName() {
39 return name;
40 }
41
42 public void setName(String name) {
43 this.name = name;
44 }
45
46 public int getAge() {
47 return age;
48 }
49
50 public void setAge(int age) {
51 this.age = age;
52 }
53 }
2>.编写Order类
1 /*
2 @author :yinzhengjie
3 Blog:http://www.cnblogs.com/yinzhengjie/tag/Java%E5%9F%BA%E7%A1%80/
4 EMAIL:y1053419035@qq.com
5 */
6 package cn.org.yinzhengjie.mybatis.domain.one2many;
7
8 /**
9 * 订单
10 */
11 public class Order {
12 private Integer id ;
13 private String orderno ;
14 private float price ;
15 //建立从Order到Customer之间多对一关联关系
16 private Customer customer ;
17
18 public Integer getId() {
19 return id;
20 }
21
22 public void setId(Integer id) {
23 this.id = id;
24 }
25
26 public String getOrderno() {
27 return orderno;
28 }
29
30 public void setOrderno(String orderno) {
31 this.orderno = orderno;
32 }
33
34 public float getPrice() {
35 return price;
36 }
37
38 public void setPrice(float price) {
39 this.price = price;
40 }
41
42 public Customer getCustomer() {
43 return customer;
44 }
45
46 public void setCustomer(Customer customer) {
47 this.customer = customer;
48 }
49 }
三.编写配置文件
1>.mybatis-config.xml 文件内容
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 <properties>
7 <property name="driver" value="com.mysql.jdbc.Driver"/>
8 <property name="url" value="jdbc:mysql://localhost:5200/yinzhengjie"/>
9 <property name="username" value="root"/>
10 <property name="password" value="yinzhengjie"/>
11 </properties>
12
13 <!-- 我们使用typeAliases标签给我们自定义类起个别名。-->
14 <typeAliases>
15 <typeAlias type="cn.org.yinzhengjie.mybatis.domain.one2many.Customer" alias="_Customer" />
16 <typeAlias type="cn.org.yinzhengjie.mybatis.domain.one2many.Order" alias="_Order" />
17 </typeAliases>
18
19 <environments default="development">
20 <environment id="development">
21 <transactionManager type="JDBC"/>
22 <dataSource type="POOLED">
23 <property name="driver" value="${driver}"/>
24 <property name="url" value="${url}"/>
25 <property name="username" value="${username}"/>
26 <property name="password" value="${password}"/>
27 </dataSource>
28 </environment>
29 </environments>
30 <mappers>
31 <!-- 我们使用mapper标签指定映射文件，使用resource指定具体的路径，如果没有写绝对路径，默认的根路径就在resources目录中-->
32 <mapper resource="CustomerMapper.xml"/>
33 <mapper resource="OrderMapper.xml"/>
34 </mappers>
35 </configuration>
2>.OrderMapper.xml 文件内容
1 <?xml version="1.0" encoding="UTF-8" ?>
2 <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
3 "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
4 <!-- 定义名字空间 -->
5 <mapper namespace="orders">
6 <insert id="insert">
7 <!-- 注意，我们传递的参数 #{customer.id}是对象的属性，因此，这里千万别写cid，尽管我们在创建数据库中定义的有这个字段，但是我们在定义类的时候是把它定义为对象的一个属性！ -->
8 insert into orders(orderno, price , cid) values(#{orderno}, #{price} , #{customer.id}) ;
9 </insert>
10
11 <!--用resultMap标签定义数据库的查询结果映射，这个结果不能直接和我们自定义的类进行交互，需要通过resultMap标签定义结果映射才能使用我们自定义的类接收数据。-->
12 <select id="selectOne" resultMap="rm_Order">
13 SELECT
14 <!-- 定义需要查询的别名 -->
15 o.id oid ,
16 o.orderno oorderno ,
17 o.price oprice ,
18 o.cid ocid ,
19 c.id cid ,
20 c.name cname ,
21 c.age cage
22 FROM
23 <!-- 定义需要查询的字段 -->
24 orders o
25 <!-- 使用左外连接查询 -->
26 LEFT OUTER JOIN customers c on o.cid = c.id
27 where
28 o.id = #{id}
29 </select>
30 <select id="selectAll" resultMap="rm_Order">
31 SELECT
32 o.id oid ,
33 o.orderno oorderno ,
34 o.price oprice ,
35 o.cid ocid ,
36 c.id cid ,
37 c.name cname ,
38 c.age cage
39 FROM
40 orders o
41 LEFT OUTER JOIN customers c on o.cid = c.id
42 </select>
43
44 <!-- 使用resultMap标签定义结果映射，即将id为"rm_Order"的查询结果和我们自定义的类做一个关联关系，否则直接拿查询出来的结果字段和我们自定义的字段是对应不上的！-->
45 <resultMap id="rm_Order" type="_Order">
46 <!--将查询结果“oid”字段对应为我们自定义别名类“_Order”的“id"字段-->
47 <id column="oid" property="id" />
48 <result column="oorderno" property="orderno"/>
49 <result column="oprice" property="price"/>
50
51
52 <!-- 多对一关联关系 -->
53 <!-- 使用association这个标签可以建立关联属性， property表示"_Order"的属性，column是通过上面定义的"ocid"别名来查询的，而javaType表示指定"customer"岁对应的属性为"_Customer" -->
54 <association property="customer" column="ocid" javaType="_Customer">
55 <!--下面就是具体的对应关系。-->
56 <id column="cid" property="id" />
57 <result column="cname" property="name" />
58 <result column="cage" property="age" />
59 </association>
60 </resultMap>
61 </mapper>
3>.CustomerMapper.xml 文件内容
1 <?xml version="1.0" encoding="UTF-8" ?>
2 <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
3 "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
4 <!-- 定义名字空间 -->
5 <mapper namespace="customers">
6 <!-- useGeneratedKeys的值为true时，表示需要使用数据库深层的keys，同时我们需要指定使用哪个深层的key。而指定具体使用哪个key我们使用keyProperty来定义！ -->
7 <insert id="insert" useGeneratedKeys="true" keyProperty="id">
8 <!-- 注意，#{name}, #{age}中的name和age字样必须和我们自定义类要一致哟！ -->
9 insert into customers(name, age) values(#{name}, #{age}) ;
10 </insert>
11
12 <!--用resultMap标签定义数据库的查询结果映射，这个结果不能直接和我们自定义的类进行交互，需要通过resultMap标签定义结果映射才能使用我们自定义的类接收数据。-->
13 <select id="selectOne" resultMap="rm_Customer">
14 select
15 c.id cid ,
16 c.name cname ,
17 c.age cage ,
18 o.id oid ,
19 o.orderno oorderno ,
20 o.price oprice ,
21 o.cid ocid
22 from
23 customers c left outer join orders o on o.cid = c.id
24 where
25 c.id = #{id} ;
26 </select>
27
28 <resultMap id="rm_Customer" type="_Customer">
29 <id column="cid" property="id"/>
30 <result column="cname" property="name"/>
31 <result column="cage" property="age"/>
32 <!--使用collection这个标签可以建立关联属性。多对一关系映射-->
33 <collection property="orders" ofType="_Order" column="ocid">
34 <id column="oid" property="id"/>
35 <result column="oorderno" property="orderno" />
36 <result column="oprice" property="price"/>
37 </collection>
38 </resultMap>
39
40 </mapper>
四.编写测试代码
1>.编写测试代码如下：
1 /*
2 @author :yinzhengjie
3 Blog:http://www.cnblogs.com/yinzhengjie/tag/Java%E5%9F%BA%E7%A1%80/
4 EMAIL:y1053419035@qq.com
5 */
6 package cn.org.yinzhengjie.mybatis.test;
7
8 import cn.org.yinzhengjie.mybatis.domain.one2many.Customer;
9 import cn.org.yinzhengjie.mybatis.domain.one2many.Order;
10 import org.apache.ibatis.io.Resources;
11 import org.apache.ibatis.session.SqlSession;
12 import org.apache.ibatis.session.SqlSessionFactory;
13 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
14 import org.junit.Test;
15
16 import java.io.InputStream;
17 import java.util.List;
18
19
20 public class TestOne2Many {
21 /**
22 * 测试往Customer插入指定的数据
23 */
24 @Test
25 public void testInsertCustomer() throws Exception {
26 InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
27 SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(in);
28 SqlSession sess = sf.openSession();
29 Customer c = new Customer();
30 c.setName("yinzhengjie");
31 c.setAge(18);
32 sess.insert("customers.insert", c);
33
34 Order o = new Order();
35 o.setOrderno("no001");
36 o.setPrice(100);
37 //设置关联关系
38 o.setCustomer(c);
39
40 sess.insert("orders.insert" , o) ;
41 sess.commit();
42 sess.close();
43 }
44
45 /**
46 * 测试查询指定的order
47 */
48 @Test
49 public void testSelectOneOrder() throws Exception {
50 InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
51 SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(in);
52 SqlSession sess = sf.openSession();
53 Order o = sess.selectOne("orders.selectOne" , 1);
54 System.out.println(o.getOrderno());
55 List<Order> orders = sess.selectList("orders.selectAll");
56 for(Order obj : orders){
57 System.out.print(obj.getOrderno());
58 Customer c = obj.getCustomer() ;
59 if(c != null){
60 System.out.println(c.getName());
61 }
62 else{
63 System.out.println();
64 }
65 }
66 sess.commit();
67 sess.close();
68 }
69
70
71 /**
72 * 测试查询指定的Customer
73 */
74 @Test
75 public void testSelectCustomer() throws Exception {
76 InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
77 SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(in);
78 SqlSession sess = sf.openSession();
79 Customer c = sess.selectOne("customers.selectOne" , 1);
80 for(Order o : c.getOrders()){
81 System.out.println(o.getId() + " " + o.getOrderno());
82 }
83 sess.commit();
84 sess.close();
85 }
86 }
2>.查询数据库执行结果如下：
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