Mybatis reultMap实现一对一的映射

川长思鸟来 2022-03-02 07:44 180阅读 0赞

在数据库中创建两张简单的表user表和orders表，orders中userId是orders的外键，同时是user表的主键,Pojo对象与数据库的字段一一对应  
User.java

package per.czt.ssm.domain;
    
    public class User {
    	private Integer id;
    	private String username;
    	
    	private String password;
    	private Integer grade;
    	public Integer getId() {
    		return id;
    	}
    	public void setId(Integer id) {
    		this.id = id;
    	}
    	public String getUsername() {
    		return username;
    	}
    	public void setUsername(String username) {
    		this.username = username;
    	}
    	public String getPassword() {
    		return password;
    	}
    	public void setPassword(String password) {
    		this.password = password;
    	}
    	public Integer getGrade() {
    		return grade;
    	}
    	public void setGrade(Integer grade) {
    		this.grade = grade;
    	}
    	
    	
    }

Orders.java

package per.czt.ssm.domain;
    
    public class Orders {
    	private Integer id;
    	private User user;
    	public Integer getId() {
    		return id;
    	}
    	public void setId(Integer id) {
    		this.id = id;
    	}
    	public User getUser() {
    		return user;
    	}
    	public void setUser(User user) {
    		this.user = user;
    	}
    	
    	
    }

我这里把两个都写在一个映射文件去了  
Mapper.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="per.czt.ssm.domain">
    
    	
    	
    	<resultMap type="per.czt.ssm.domain.Orders" id="Orders">
    		<result property="id" column="oid"/>
    		<result property="user" column="userId"/>
    		<association property="user" javaType="per.czt.ssm.domain.User" >
    			<id  property="id" column="uid"/>
    		    <result property="username" column="username"/>
    	        <result property="password" column="password"/>
    		</association>
    	
    	</resultMap>
    	
    
    	
    	<select id="searchOrders" parameterType="per.czt.ssm.domain.Orders"
    		resultMap="Orders">
    		select * from orders,user where orders.userId=user.uid
    	</select>
    	
    
    </mapper>

在Dao层调用这个查询语句

@Override
    	public List<Orders> listAll() {
    		
    		return this.getSqlSession().selectList("per.czt.ssm.domain.searchOrders", null);
    	}

在Service层调用dao

@Override
    	public List<Orders> listAll() {
    		
    		return ordersDao.listAll();
    	}

在controller调用service，然后通过model设置attribute传递给view层

@RequestMapping("/listAll")
    	public String listAll(Model model)
    	{
    		System.out.println("OrdersController");
    		List<Orders> ordersList=ordersService.listAll();
    		for(Orders order:ordersList)
    		{
    			System.out.println("id:"+order.getId()+" "+"userId:"+order.getUser().getId());
    		}
    		System.out.println("ordersList.size():"+ordersList.size());
    		model.addAttribute(ordersList);
    		
    		return "/orders/ordersList";
    	}

最后在view层显示

<table border="1">
    		<thead>
    			<tr>
    				<th>id</th>
    				<th>userId</th>
    				<th>username</th>
    			
    			
    			</tr>
    
    		</thead>
    		<tbody>
    			<c:forEach items="${ordersList }" var="orders">
    				<tr>
    					<td>${orders.id }</td>
    					<td>${orders.user.id}</td>
    					<td>${orders.user.username}</td>
    					
    				</tr>
    
    			</c:forEach>
    
    
    		</tbody>
    
    	</table>