Java代码示例 resultMap collection

好的，以下是一个Java代码示例，使用MyBatis中的resultMap和collection来映射结果集：

public interface OrderMapper {
    @Select("SELECT * FROM orders WHERE customer_id = #{customerId}")
    @Results(id = "orderResult", value = {
            @Result(property = "id", column = "id"),
            @Result(property = "orderNumber", column = "order_number"),
            @Result(property = "orderItems", javaType = List.class, column = "id",
                    many = @Many(select = "com.example.OrderItemMapper.getOrderItemsByOrderId"))
    })
    List<Order> getOrdersByCustomerId(int customerId);
}

public interface OrderItemMapper {
    @Select("SELECT * FROM order_items WHERE order_id = #{orderId}")
    @Results(value = {
            @Result(property = "id", column = "id"),
            @Result(property = "productId", column = "product_id"),
            @Result(property = "quantity", column = "quantity")
    })
    List<OrderItem> getOrderItemsByOrderId(int orderId);
}

public class Order {
    private int id;
    private String orderNumber;
    private List<OrderItem> orderItems;
    // getters and setters
}

public class OrderItem {
    private int id;
    private int productId;
    private int quantity;
    // getters and setters
}

在上面的示例中，OrderMapper接口使用了一个@Results注解来定义一个名为"orderResult"的resultMap。这个resultMap定义了如何将查询结果映射到Order对象中，包括Order对象中的orderItems字段。

@Many注解指定了如何获取orderItems，它将调用OrderItemMapper接口中的getOrderItemsByOrderId方法来获取与当前订单相关的所有订单项。

OrderItemMapper接口中的@Results注解定义了如何将查询结果映射到OrderItem对象中。

最后，Order和OrderItem类只是简单的POJO，它们包含了与数据库表中的列对应的属性。