Java中ResultMap的嵌套查询映射

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：

    
    
    
    



    
    
    



    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 id as customer_id, name as customer_name, email as customer_email
    FROM customers
    WHERE id = #{customerId}

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。