Mybatis框架-13：多表操作之多对一

心已赠人 2022-01-23 08:51 200阅读 0赞

# 第一步：建立两张表并建立外键联系 #

我这里是客户与订单的表进行举例

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MTk4NDY3_size_16_color_FFFFFF_t_70][]

# 第二步：建立对应关系的映射类（domain） #

customer类

@Data
    public class Customer {
        private Integer cust_id;
        private String cust_name;
        private String cust_profession;
        private String cust_phone;
        private String email;
    
    }

order类

@Data
    public class Order {
        private Integer orderId;
        private String orderName;
        private String orderNum;
        private Customer customer;
    }

# 第三步：编写mapper #

public interface OrderMapper {
        public List<Order> getAllOrder();
    }

# 第四步:编写mapper.xml #

方式一：association（建议使用）

<resultMap id="orderMap" type="com.ctbu.domain.Order">
            <result property="orderId" column="orderId"/>
            <result property="orderName" column="orderName"/>
            <result property="orderNum" column="orderNum"/>
    
            <association property="customer" javaType="Customer">
                <id property="cust_id" column="cust_id"/>
                <result property="cust_name" column="cust_name"/>
                <result property="cust_phone" column="cust_phone"/>
                <result property="cust_profession" column="cust_profession"/>
                <result property="email" column="email"/>
            </association>
        </resultMap>
    
        <select id="getAllOrder" resultMap="orderMap">
            SELECT * from `order` as o LEFT JOIN `customer` as c ON o.orderCustId=c.cust_id;
        </select>

方式二：级联封装（一般不适用）

<resultMap id="orderMap" type="com.ctbu.domain.Order">
            <result property="orderId" column="orderId"/>
            <result property="orderName" column="orderName"/>
            <result property="orderNum" column="orderNum"/>
    
            <result property="customer.cust_id" column="cust_id"/>
            <result property="customer.cust_name" column="cust_name"/>
            <result property="customer.cust_phone" column="cust_phone"/>
            <result property="customer.cust_profession" column="cust_profession"/>
            <result property="customer.email" column="email"/>
        </resultMap>
    
        <select id="getAllOrder" resultMap="orderMap">
            SELECT * from `order` as o LEFT JOIN `customer` as c ON o.orderCustId=c.cust_id;
        </select>

# 第五步：测试程序 #

@Test
        public void test4(){
            SqlSession session = MyUtils.openSession();
            OrderMapper mapper = session.getMapper(OrderMapper.class);
            List<Order> allOrder = mapper.getAllOrder();
            for (Order order : allOrder) {
                System.out.println(order);
            }
            session.close();
        }

结果：

![20190603121110458.png][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MTk4NDY3_size_16_color_FFFFFF_t_70]: /images/20220123/aa119aabc97b4b129ff4ab82cad05d8a.png
[20190603121110458.png]: /images/20220123/e8dc333ca9634a91be565f73c9173d15.png