mybatis一对一查询

分手后的思念是犯贱 2022-03-10 05:20 280阅读 0赞

**方法一：使用resultType**

> 使用resultType，通过继承改造pojo类，此pojo类中包括了两个类字段信息，这样返回对象的时候，mybatis自动把信息也注入进来。定义专门的pojo类作为输出类型，其中定义了sql查询结果集所有的字段。

public class OrderUser extends Orders{
    	private String username;
    	private String address;
    	public String getUsername() {
    		return username;
    	}
    	public void setUsername(String username) {
    		this.username = username;
    	}
    	public String getAddress() {
    		return address;
    	}
    	public void setAddress(String address) {
    		this.address = address;
    	}
    	
    }

**mapper.xml**

<select id="queryOrderUser" resultType="com.it.mybatis.pojo.OrderUser">
    		SELECT
    		o.id,
    		o.user_id
    		userId,
    		o.number,
    		o.createtime,
    		o.note,
    		u.username,
    		u.address
    		FROM
    		`orders` o
    		LEFT JOIN `user` u ON o.user_id = u.id
    	</select>

接口：

![20190309182846499.png][]

**方法二：使用resultMap**

> 使用resultMap，定义专门的resultMap用于映射一对一查询结果。

**改造pojo类**

在Order类中加入User属性，user属性中用于存储关联查询的用户信息，因为订单关联查询用户是一对一关系，所以这里使用单个User对象存储关联查询的用户信息。

> private User user;

public class Orders  implements Serializable{
        /**
    	 * 
    	 */
    	private static final long serialVersionUID = 1L;
    
    	private Integer id;
    
        private Integer userId;
    
        private String number;
    
        private Date createtime;
    
        private String note;
    
        private User user;
        
        
        
        public User getUser() {
    		return user;
    	}
    
    	public void setUser(User user) {
    		this.user = user;
    	}
    
    	public Integer getId() {
            return id;
        }
    
        public void setId(Integer id) {
            this.id = id;
        }
    
        public Integer getUserId() {
            return userId;
        }
    
        public void setUserId(Integer userId) {
            this.userId = userId;
        }
    
        public String getNumber() {
            return number;
        }
    
        public void setNumber(String number) {
            this.number = number == null ? null : number.trim();
        }
    
        public Date getCreatetime() {
            return createtime;
        }
    
        public void setCreatetime(Date createtime) {
            this.createtime = createtime;
        }
    
        public String getNote() {
            return note;
        }
    
        public void setNote(String note) {
            this.note = note == null ? null : note.trim();
        }
    
    	@Override
    	public String toString() {
    		return "Orders [id=" + id + ", userId=" + userId + ", number=" + number + ", createtime=" + createtime
    				+ ", note=" + note + "]";
    	}
        
        
        
        
    }

**Mapper.xml**

<resultMap type="com.it.mybatis.pojo.Orders" id="orderUserResultMap">
    		<id property="id" column="id" />
    		<result property="userId" column="user_id" />
    		<result property="number" column="number" />
    		<result property="createtime" column="createtime" />
    		<result property="note" column="note" />
    
    		
    		
    		
    		<association property="user" javaType="com.it.mybatis.pojo.User">
    			
    			<id property="id" column="user_id" />
    			<result property="username" column="username" />
    			<result property="address" column="address" />
    		</association>
    
    	</resultMap>
    
    	
    	<select id="queryOrderUserResultMap" resultMap="orderUserResultMap">
    		SELECT
    		o.id,
    		o.user_id,
    		o.number,
    		o.createtime,
    		o.note,
    		u.username,
    		u.address
    		FROM
    		`orders` o
    		LEFT JOIN `user` u ON o.user_id = u.id
    	</select>

[20190309182846499.png]: /images/20220310/a253453f7bdb40a68a0a73b42fded346.png