使用 DataMapper 的外键和关联
我已经非常彻底地阅读了此页面：
http://datamapper.org/docs/associations
如果答案是在那里，它根本没有以我能理解的方式表达。
我对通过 Datamapper 设置关系感到非常困惑。上面的 datamapper 网站几乎是我能找到的关于该主题的所有内容，正如我所说，它并不是特别有帮助。
例如，如果我想创建如下所示的内容：
表：users
id (primary key)
name
表：attributes
id (pk)
title
表：user_attributes
id (pk)
user_id (fk to users.id)
attribute_id (fk to attributes.id)
value
这看起来很简单，但它已经非常困难了。我尝试的所有操作都会给我带来错误，例如在 UserUserAttribute (DataMapper::UnknownRelationshipError) 中没有名为 user_attributes 或 user_attribute 的关系
有人可以告诉我这个简单映射的类定义，也许可以指出我更好的讨论数据映射器协会？以下是我尝试过的一些方法。
class User
include DataMapper::Resource
property :id, Serial, :key => true
property :name, String
has n, :user_attributes, :through=>:attribute
end
class Attribute
include DataMapper::Resource
property :id, Serial, :key => true
property :name, String
has n, :user_attributes, :through=>:user
end
class UserAttribute
include DataMapper::Resource
belongs_to :user
belongs_to :attribute
end
I have read this page quite thoroughly:
http://datamapper.org/docs/associations
If the answer is on there, it's simply not expressed in a way I can understand.
I'm very confused about using setting up relationship via Datamapper. The datamapper site above is pretty much all I can find on the topic, and as I've said, it hasn't been particularly helpful.
For example, if I want to create something like the following:
Table: users
id (primary key)
name
Table: attributes
id (pk)
title
Table: user_attributes
id (pk)
user_id (fk to users.id)
attribute_id (fk to attributes.id)
value
This seems simple enough, but it has been prohibitively difficult. Everything I try gives me errors like No relationships named user_attributes or user_attribute in UserUserAttribute (DataMapper::UnknownRelationshipError)
Can someone please tell me the class definitions for this simple mapping, and perhaps point me to a better discussion of DataMapper associations? Below is some of what I've tried.
class User
include DataMapper::Resource
property :id, Serial, :key => true
property :name, String
has n, :user_attributes, :through=>:attribute
end
class Attribute
include DataMapper::Resource
property :id, Serial, :key => true
property :name, String
has n, :user_attributes, :through=>:user
end
class UserAttribute
include DataMapper::Resource
belongs_to :user
belongs_to :attribute
end
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评论（2）
我认为您会看到类似
UserUserAttribute的内容，因为 DataMapper 正在尝试自动生成匿名连接类。这是一篇文章，介绍如何命名多个DataMapper 中的对多关系
您可能会更改示例，如下所示：
I think you're seeing things like
UserUserAttributebecause DataMapper is trying to auto-generate an anonymous join class.Here's an article that describes how to make named many-to-many relationships in DataMapper
You would probably change the example something like this:
问题是您的类是 UserAttribute，并且您试图用 user_attributes 命名关系。去掉下划线，你的问题就会消失（或者在类名中添加下划线）
The issue is that your class is UserAttribute, and you're trying to name the relationships with user_attributes. Get rid of the underscore, and your issue will disappear (or add an underscore to the class name)