一.在数据库中建立相应的表
use mybatis ;
-- 删除表
drop table if exists items ;
drop table if exists orders ;
drop table if exists users ;
-- 创建表
create table users(id int primary key auto_increment , name
varchar(20) , age int);
create table orders(id int primary key auto_increment ,
orderno varchar(20) , uid int);
create table items(id int primary key auto_increment ,
itemname varchar(20) , oid int);
-- 插入用户
insert into users(name,age) values('tom',12);
insert into users(name,age) values('tomas',13);
-- 插入订单
insert into orders(orderno,uid) values('No001',1);
insert into orders(orderno,uid) values('No002',1);
insert into orders(orderno,uid) values('No003',2);
insert into orders(orderno,uid) values('No004',2);
-- 插入订单项
insert into items(itemname,oid) values('item001',1);
insert into items(itemname,oid) values('item002',1);
insert into items(itemname,oid) values('item003',2);
insert into items(itemname,oid) values('item004',2);
insert into items(itemname,oid) values('item005',3);
insert into items(itemname,oid) values('item006',3);
insert into items(itemname,oid) values('item007',4);
insert into items(itemname,oid) values('item008',5);
select * from users ;
select * from orders ;
select * from items ;
二.建立实体类，用于去映射数据库中的表
-
建立类
[Order.java] public class Order { private Integer id ; private String orderNo ; //简历关联关系 private User user ; //get/set } [Item.java] public class Item { private Integer id; private String itemName; //订单项和订单之间的关联关系 private Order order; //get/set } -
引入映射文件
<mappers> <mapper resource="UserMapper.xml"/> <mapper resource="OrderMapper.xml"/> </mappers> -
测试类
@Test public void selectOne() throws Exception { String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(inputStream); SqlSession s = sf.openSession(); Order order = s.selectOne("orders.selectOne",1); System.out.println(order.getOrderNo()); s.commit(); s.close(); } @Test public void selectAll() throws Exception { String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(inputStream); SqlSession s = sf.openSession(); List<Order> list = s.selectList("orders.selectAll"); for(Order o : list){ System.out.println(o.getOrderNo() + " : " + o.getUser().getName()); } s.commit(); s.close(); }
三.配置一对多的应用
-
1.在User中增加orders集合。
public class User { ... private List<Order> orders ; //get/set }- 2.改造UserMapper.xml
<!-- selectOne -->
<select id="selectOne" parameterType="int" resultMap="RM_User">
select
u.id uid ,
u.name uname ,
u.age uage ,
o.id oid ,
o.orderno oorderno
from users u
left outer join orders o on u.id = o.uid
where u.id = #{id}
</select>
<resultMap id="RM_User" type="_User">
<id property="id" column="uid" />
<result property="name" column="uname" />
<result property="age" column="uage" />
<!-- 映射一对多关联关系 -->
<collection property="orders" ofType="_Order">
<id property="id" column="oid" />
<result property="orderNo" column="oorderno" />
</collection>
</resultMap>
<!-- selectAll -->
<select id="selectAll" resultMap="RM_User">
select
u.id uid ,
u.name uname ,
u.age uage ,
o.id oid ,
o.orderno oorderno
from users u
left outer join orders o on u.id = o.uid
</select>
四.组合多对一和一对多关联关系到一个实体(Order)中
-
1.关系
Order() -> (1)User
Order(1) -> ()Item -
2.Order.java
class Order{
...
List<Item> items ;
//get/set
}
2'.修改配置文件增加别名
[resources/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>
<typeAliases>
<typeAlias type="com.it18zhang.mybatisdemo.domain.User" alias="_User"/>
<typeAlias type="com.it18zhang.mybatisdemo.domain.Order" alias="_Order"/>
<typeAlias type="com.it18zhang.mybatisdemo.domain.Item" alias="_Item"/>
</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>
<!-- 引入映射文件 -->
<mappers>
<mapper resource="UserMapper.xml"/>
<mapper resource="OrderMapper.xml"/>
</mappers>
</configuration>
-
3.OrderMapper.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="orders"> <insert id="insert"> insert into orders(orderno,uid) values(#{orderNo},#{user.id}) </insert> <!-- findById --> <select id="selectOne" parameterType="int" resultMap="RM_Order"> select o.id oid , o.orderno oorderno , o.uid uid , u.name uname , u.age uage , i.id iid, i.itemname iitemname from orders o left outer join users u on o.uid = u.id left outer join items i on o.id = i.oid where o.id = #{id} </select> <!-- findAll --> <select id="selectAll" resultMap="RM_Order"> select o.id oid , o.orderno oorderno , o.uid uid , u.name uname , u.age uage , i.id iid, i.itemname iitemname from orders o left outer join users u on o.uid = u.id left outer join items i on o.id = i.oid </select> <!-- 自定义结果映射 --> <resultMap id="RM_Order" type="com.it18zhang.mybatisdemo.domain.Order"> <id property="id" column="oid"/> <result property="orderNo" column="oorderno"/> <association property="user" javaType="com.it18zhang.mybatisdemo.domain.User"> <id property="id" column="uid" /> <result property="name" column="uname" /> <result property="age" column="uage" /> </association> <collection property="items" ofType="_Item"> <id property="id" column="iid" /> <result property="itemName" column="iitemname" /> </collection> </resultMap> </mapper> -
4.测试
@Test public void selectOne() throws Exception { String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(inputStream); SqlSession s = sf.openSession(); Order order = s.selectOne("orders.selectOne",1); System.out.println(order.getOrderNo() + order.getUser().getName()); for(Item i : order.getItems()){ System.out.println(i.getId() + ":" + i.getItemName()); } s.commit(); s.close(); }
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