关系型数据库

一对多

实体类

package com.wzx.pojo;


import java.util.List;

public class Customer {
    private Integer id;
    private String name;
    private Integer age;
    //该客户名下的所有订单的集合
    private List ordersList;

    public Customer() {
    }

    public Customer(Integer id, String name, Integer age, List ordersList) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.ordersList = ordersList;
    }

    @Override
    public String toString() {
        return "Customer{" +
                "id=" + id +
                ", name='" + name + ''' +
                ", age=" + age +
                ", ordersList=" + ordersList +
                '}';
    }

    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 getOrdersList() {
        return ordersList;
    }

    public void setOrdersList(List ordersList) {
        this.ordersList = ordersList;
    }
}

package com.wzx.pojo;

public class Orders {
    private Integer id;
    private String orderNumber;
    private Double orderPrice;

    //关联下次订单的客户信息，多方持有一方的对象
    private Customer customer;

    @Override
    public String toString() {
        return "Orders{" +
                "id=" + id +
                ", orderNumber='" + orderNumber + ''' +
                ", orderPrice=" + orderPrice +
                ", 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 Customer getCustomer() {
        return customer;
    }

    public void setCustomer(Customer customer) {
        this.customer = customer;
    }

    public Orders(Integer id, String orderNumber, Double orderPrice, Customer customer) {
        this.id = id;
        this.orderNumber = orderNumber;
        this.orderPrice = orderPrice;
        this.customer = customer;
    }

    public Orders() {
    }


}

接口

package com.wzx.mapper;

import com.wzx.pojo.Customer;

public interface CustomerMapper {
    //根据客户的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);
}

接口实现 

    
    
    
        
        
        
        
        
        
        
            
            
            
            
            
            
        
    
    
    select c.id cid,name,age,o.id oid,orderNumber,orderPrice,customer_id
    from customer c left join orders o on c.id=o.customer_id
    where c.id=#{id}
    

 测试类

public class MyTest {
    SqlSession sqlSession;
    CustomerMapper customerMapper;
    OrdersMapper ordersMapper;

    @Before
    public void openSqlSession() throws IOException {
        //读取核心配置文件
        InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
        //创建SqlSessionFactory对象
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
        //取出SqlSession对象
        sqlSession = factory.openSession();
        customerMapper = sqlSession.getMapper(CustomerMapper.class);
        ordersMapper = sqlSession.getMapper(OrdersMapper.class);
    }

    @After
    public void closeSqlSession() {
        sqlSession.close();
    }

    @Test
    public void getById() {
        Customer byId = customerMapper.getById(3);
        System.out.println(byId);
    }

 多对一

接口类

package com.wzx.mapper;

import com.wzx.pojo.Orders;
import org.apache.ibatis.annotations.Mapper;

import java.util.List;


public interface OrdersMapper {
    //根据主键查订单，并同时查询下此订单的客户信息
    Orders getById(Integer id);

}

接口实现

    
        
        
        
        
        
        
        
        
        
        
        
            
            
            
            
            
            
        
    
    
    
        select c.id cid, name, age, o.id oid, orderNumber, orderPrice, customer_id
        from orders o
                     inner join customer c on c.id = o.customer_id
        where o.id = #{id}
    
    
    select * from orders
    

 测试类

    @Test
    public void getById1() {
        Orders byId = ordersMapper.getById(11);
        System.out.println(byId);
    }