Linq：在选择列表中获取多态实体

发布于 2024-11-05 10:12:01 字数 206 浏览 0 评论 0原文

我想要执行以下操作...

FROM o IN orders
SELECT new OrderContainer { Contact = (PostalContact) o.Contact  }

所以希望您可以看到订单的“联系人”将是派生类型。但不幸的是，它似乎没有进行多态获取！有办法实现这个目标吗？

干杯，伊恩。

原文

I want to do the following...

FROM o IN orders
SELECT new OrderContainer { Contact = (PostalContact) o.Contact  }

So hopefully you can see that the order's 'Contact' will be of a derived type. Unfortunately however it doesn't seem to do a polymorphic fetch! Is there anyway of achieving this?

Cheers, Ian.

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拥醉 2024-11-12 10:12:01

尝试使用扩展方法 .OfType()

from o in orders 
select new OrderContainer { Contact = o.Contact.OfType<PostalContact>().FirstOrDefault() }

编辑：

一种获取完整对象数据的方法，但我怀疑这是否足以满足您的需求。

from c in contacts.OfType<PostalContact>()
where c.Orders.Any(o=>o.Contact.Id == c.id)    
select new OrderContainer { Contact = c }

另一方面，如果将基类（实体）设置为抽象，您可能会发现实体将加载完整的对象。但由于会生成查询，因此不建议这样做。如果您正在研究此问题，您可能需要查看联系人的每个层次结构的 (TPH) 表

Try using the extention method .OfType()

from o in orders 
select new OrderContainer { Contact = o.Contact.OfType<PostalContact>().FirstOrDefault() }

Edit:

a way to get the full object data, but i doubt that this is good enough for your needs.

from c in contacts.OfType<PostalContact>()
where c.Orders.Any(o=>o.Contact.Id == c.id)    
select new OrderContainer { Contact = c }

on the other hand, if you set the base class (entity) to abstract, you may find that entity will load the full objects. but this is not recomended due to the queries that are generated. if you are looking into this you may want to look at (TPH) Table per Hierarchy for your contacts

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