用户和订单的需求
通过查询订单，查询用户，就是一对一查询
（1）自定义JavaBean（常用，推荐使用）
<select id="queryOrderUser" resultType="OrderUser">
SELECT o.id,o.user_id,u.name,o.productname
FROM t_order o LEFT JOIN t_user u ON o.user_id= u.id
</select>
OrderUser.java：
package cn.sm1234.domain;
public class OrderUser extends Order {
//Order中没有name
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
@Test
public void test1() {
SqlSession sqlSession = SessionUtils.getSession();
// getMapper(): 返回指定接口的动态代理的实现类对象
OrderDao dao = sqlSession.getMapper(OrderDao.class);
List<OrderUser> list = dao.queryOrderUser();
for (OrderUser orderUser : list) {
System.out.println(orderUser.getName()+"-"+orderUser.getProductname());
}
sqlSession.commit();
sqlSession.close();
}
OrderDao.java：
public interface OrderDao {
/**
* 查询订单，并且关联查询用户信息
*/
public List<OrderUser> queryOrderUser();
}
（2）ResultMap封装
<!-- type="实体类" -->
<resultMap type="Order" id="OrderUserResultMap">
<id column="id" property="id"/>
<result column="productname" property="productname"/>
<result column="orderno" property="orderno"/>
<!-- user_id封装到User中 -->
<!-- 关联属性
property：关联属性名称（Order类中的user）
javaType：类型（User （即User user））
-->
<association property="user" javaType="User">
<!-- column中的字段名称应该为当前查询结果的字段名称 -->
<id column="user_id" property="id"/>
<result column="name" property="name"/>
<result column="password" property="password"/>
</association> </resultMap> <select id="queryOrderUserResultMap" resultMap="OrderUserResultMap">
SELECT o.id,o.user_id,u.name,o.productname
FROM t_order o LEFT JOIN t_user u ON o.user_id= u.id
</select>
Order.java：
package cn.sm1234.domain;
public class Order {
private Integer id;
private String productname;
private String orderno;
private Integer userId;
private User user;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getProductname() {
return productname;
}
public void setProductname(String productname) {
this.productname = productname;
}
public String getOrderno() {
return orderno;
}
public void setOrderno(String orderno) {
this.orderno = orderno;
}
public Integer getUserId() {
return userId;
}
public void setUserId(Integer userId) {
this.userId = userId;
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
}
/**
* 查询订单，查询用户（ResultMap）
* @return
*/
public List<Order> queryOrderUserResultMap();
@Test
public void test2() {
SqlSession sqlSession = SessionUtils.getSession();
// getMapper(): 返回指定接口的动态代理的实现类对象
OrderDao dao = sqlSession.getMapper(OrderDao.class);
List<Order> list = dao.queryOrderUserResultMap();
for (Order order : list) {
System.out.println(order.getProductname()+"-"+order.getUser().getName());
}
sqlSession.commit();
sqlSession.close();
}