Java

Java中ResultMap的嵌套查询映射

小樊
89
2024-08-11 02:40:38
栏目: 编程语言

在Java中,如果需要进行嵌套查询映射,可以使用ResultMap来实现。以下是一个示例代码:

<resultMap id="orderResultMap" type="Order">
    <id property="id" column="order_id"/>
    <result property="orderDate" column="order_date"/>
    <result property="totalAmount" column="total_amount"/>
    <association property="customer" column="customer_id" javaType="Customer" select="selectCustomerById"/>
</resultMap>

<resultMap id="customerResultMap" type="Customer">
    <id property="id" column="customer_id"/>
    <result property="name" column="customer_name"/>
    <result property="email" column="customer_email"/>
</resultMap>

<select id="selectOrderWithCustomer" resultMap="orderResultMap">
    SELECT o.id as order_id, o.order_date, o.total_amount, o.customer_id, c.id as customer_id, c.name as customer_name, c.email as customer_email
    FROM orders o
    JOIN customers c ON o.customer_id = c.id
    WHERE o.id = #{orderId}
</select>

<select id="selectCustomerById" resultMap="customerResultMap">
    SELECT id as customer_id, name as customer_name, email as customer_email
    FROM customers
    WHERE id = #{customerId}
</select>

在上面的示例中,我们定义了两个ResultMap,分别用于映射Order和Customer对象。在Order对象的ResultMap中,我们使用了association标签来指定在查询Order对象时需要查询关联的Customer对象,并通过select属性指定了selectCustomerById查询语句的映射。在selectOrderWithCustomer查询语句中使用了orderResultMap来映射查询结果,从而实现了嵌套查询映射。

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