Mybatis表的关联查询
导语：
关于＜resultMap＞标签映射，＜association＞＆＜collection＞的使用：跳转文章查看
无论是什么关联关系，如果某方持有另一方的集合，则使用标签完成映射，如果某方持有另一方的对象，则使用标签完成映射。
一对多查询：
根据顾客ID查询顾客信息（一），同时将顾客名下所有订单查出（多）。
实现思路：
- 创建顾客类，存储顾客信息：
注意我们在顾客类中用List集合封装了顾客名下的订单信息。
package com.user.pojo;
import java.util.List;
public class Customer {
//customer表中的三个列
private Integer id;
private String name;
private Integer age;
//该客户名下所有订单集合
private List<Order> orderList;
@Override
public String toString() {
return "Customer{" +
"id=" + id +
", name='" + name + '\'' +
", age=" + age +
", orderList=" + orderList +
'}';
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public List<Order> getOrderList() {
return orderList;
}
public void setOrderList(List<Order> orderList) {
this.orderList = orderList;
}
public Customer(Integer id, String name, Integer age, List<Order> orderList) {
this.id = id;
this.name = name;
this.age = age;
this.orderList = orderList;
}
public Customer() {
}
}
- 创建订单类，存储订单信息：
package com.user.pojo;
public class Order {
private Integer id;
private String orderNumber;
private Double orderPrice;
@Override
public String toString() {
return "Order{" +
"id=" + id +
", orderNumber='" + orderNumber + '\'' +
", orderPrice=" + orderPrice +
'}';
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getOrderNumber() {
return orderNumber;
}
public void setOrderNumber(String orderNumber) {
this.orderNumber = orderNumber;
}
public Double getOrderPrice() {
return orderPrice;
}
public void setOrderPrice(Double orderPrice) {
this.orderPrice = orderPrice;
}
public Order(Integer id, String orderNumber, Double orderPrice) {
this.id = id;
this.orderNumber = orderNumber;
this.orderPrice = orderPrice;
}
public Order() {
}
}
- 动态代理接口：
package com.user.mapper;
import com.user.pojo.Customer;
public interface CustomerMapper {
//根据客户id查询客户所有信息并同时查询该客户名下的所有订单
Customer getById(Integer id);
}
- Mapper.xml文件：
因为我们的查询结果包括该顾客信息和顾客所有的订单信息，所以我们的返回值需要自定义一个map集合来存储。我们这里使用customermap，并将该集合作为我们的返回值类型。
DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.user.mapper.CustomerMapper">
<resultMap id="customermap" type="customer">
<id property="id" column="id">id>
<result property="name" column="name">result>
<result property="age" column="age">result>
<collection property="orderList" ofType="order">
<id property="id" column="id">id>
<result property="orderNumber" column="orderNumber">result>
<result property="orderPrice" column="orderPrice">result>
collection>
resultMap>
<select id="getById" parameterType="Integer" resultMap="customermap">
select customer.id ,name,age ,orders.id ,orderNumber ,orderPrice ,customer_id
from customer left join orders on customer.id = orders.customer_id
where customer.id = #{id}
select>
mapper>
- 测试程序：
import java.io.InputStream;
import java.util.List;
public class MyTest {
SqlSession sqlSession;
CustomerMapper customerMapper;
@Before
public void openSqlSession() throws IOException {
InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
sqlSession = factory.openSession();
customerMapper = sqlSession.getMapper(CustomerMapper.class);
}
@After
public void closeSqlSession(){
sqlSession.close();
}
@Test
public void testGetCustomerById(){
Customer customer = customerMapper.getById(1);
System.out.println(customer);
}
}
- 其余基础配置文件SqlMapConfig.xml：
DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<properties resource="jdbc.properties">properties>
<settings>
<setting name="logImpl" value="STDOUT_LOGGING"/>
settings>
<typeAliases>
<package name="com.user.pojo"/>
<package name="com.user.mapper"/>
typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC">transactionManager>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driverClassName}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
dataSource>
environment>
environments>
<mappers>
<package name="com.user.mapper">package>
mappers>
configuration>
多对一查询：
根据订单ID查询订单信息及该订单所属的顾客的信息。
实现思路：
- 创建订单类，存储订单信息：
注意我们在订单类中封装了该订单下的顾客的信息。
package com.user.pojo;
public class Order {
//订单信息
private Integer id;
private String orderNumber;
private Double orderPrice;
private Integer customer_id;
//订单所属的客户
private Customer customer;
@Override
public String toString() {
return "Order{" +
"id=" + id +
", orderNumber='" + orderNumber + '\'' +
", orderPrice=" + orderPrice +
", customer_id=" + customer_id +
", customer=" + customer +
'}';
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getOrderNumber() {
return orderNumber;
}
public void setOrderNumber(String orderNumber) {
this.orderNumber = orderNumber;
}
public Double getOrderPrice() {
return orderPrice;
}
public void setOrderPrice(Double orderPrice) {
this.orderPrice = orderPrice;
}
public Integer getCustomer_id() {
return customer_id;
}
public void setCustomer_id(Integer customer_id) {
this.customer_id = customer_id;
}
public Customer getCustomer() {
return customer;
}
public void setCustomer(Customer customer) {
this.customer = customer;
}
public Order(Integer id, String orderNumber, Double orderPrice, Integer customer_id, Customer customer) {
this.id = id;
this.orderNumber = orderNumber;
this.orderPrice = orderPrice;
this.customer_id = customer_id;
this.customer = customer;
}
public Order() {
}
}
- 创建顾客类，存储顾客信息：
package com.user.pojo;
import java.util.List;
public class Customer {
//顾客信息
private Integer id;
private String name;
private Integer age;
@Override
public String toString() {
return "Customer{" +
"id=" + id +
", name='" + name + '\'' +
", age=" + age +
'}';
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public Customer(Integer id, String name, Integer age) {
this.id = id;
this.name = name;
this.age = age;
}
public Customer() {
}
}
- 动态代理接口：
package com.user.mapper;
import com.user.pojo.Customer;
import com.user.pojo.Order;
public interface OrderMapper {
//根据主键查订单并同时查询该订单的客户信息
Order getById(Integer id);
}
- Mapper.xml文件：
因为我们的查询结果包括该订单信息和订单所属顾客的信息，所以我们的返回值需要自定义一个map集合来存储。我们这里使用customermap，并将该集合作为我们的返回值类型。
DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.user.mapper.OrderMapper">
<resultMap id="ordermap" type="order">
<id property="id" column="id">id>
<result property="orderNumber" column="orderNumber">result>
<result property="orderPrice" column="orderPrice">result>
<result property="customer_id" column="customer_id">result>
<association property="customer" javaType="customer">
<id property="id" column="id">id>
<result property="name" column="name">result>
<result property="age" column="age">result>
association>
resultMap>
<select id="getById" parameterType="Integer" resultMap="ordermap">
select orders.id ,orderNumber ,orderPrice ,customer_id ,customer.id ,name,age
from orders left join customer on orders.customer_id = customer.id
where orders.id = #{id}
select>
mapper>
- 测试类：
package com.user;
import com.user.mapper.OrderMapper;
import com.user.pojo.Order;
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.After;
import org.junit.Before;
import org.junit.Test;
import java.io.IOException;
import java.io.InputStream;
public class MyTest {
SqlSession sqlSession;
OrderMapper orderMapper;
@Before
public void openSqlSession() throws IOException {
InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
sqlSession = factory.openSession();
orderMapper = sqlSession.getMapper(OrderMapper.class);
}
@After
public void closeSqlSession(){
sqlSession.close();
}
@Test
public void testGetOrderById(){
Order order = orderMapper.getById(11);
System.out.println(order);
}
}
- 其余基础配置文件：
DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<properties resource="jdbc.properties">properties>
<settings>
<setting name="logImpl" value="STDOUT_LOGGING"/>
settings>
<typeAliases>
<package name="com.user.pojo"/>
<package name="com.user.mapper"/>
typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC">transactionManager>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driverClassName}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
dataSource>
environment>
environments>
<mappers>
<package name="com.user.mapper">package>
mappers>
configuration>
一对一查询：
同多对一。
- 实体类：
- 动态代理接口：
- mapper.xml文件：
多对多查询：
多对多关联中，需要通过中间表化解关联关系。中间表描述两张主键表的关联。