可能有＆QUOT;多态型HAS_ONE＆QUOT;在导轨的关系？ [英] Possible to have "polymorphic has_one" relationship in rails?

问题描述

我希望做这样的事情：

Category
--------
- id
- name

Tag
--------
- id
- tag


Campaign
--------
- id
- name
- target (either a tag *or* a category)

时的关联是这里的答案吗？我似乎无法弄清楚如何使用它HAS_ONE：目标：为=>：靶向

Is a polymorphic association the answer here? I can't seem to figure out how to use it with has_one :target, :as => :targetable.

基本上，我希望Campaign.target被设置为一个标签或一个类别（或潜在另一个模型在未来）。

Basically, I want Campaign.target to be set to a Tag or a Category (or potentially another model in the future).

推荐答案

我不相信你在这里需要一个 HAS_ONE 关联，则 belongs_to的应该是你正在寻找的东西。

I don't believe you're in need of a has_one association here, the belongs_to should be what you're looking for.

在这种情况下，你会希望有一个 target_id 和 TARGET_TYPE 在广告系列的表列中，您可以创建这些与一个耙t.references：目标通话（其中 T 是表变量）。

In this case, you'd want a target_id and target_type column on your Campaign table, you can create these in a rake with a t.references :target call (where t is the table variable).

class Campaign < ActiveRecord::Base
  belongs_to :target, :polymorphic => true
end

现在的运动可以关联到一个标签或类别和 @campaign。目标将返回一个合适的。

Now campaign can be associated to either a Tag or Category and @campaign.target would return the appropriate one.

在 HAS_ONE 的关联将被使用，如果你有目标表指向回到你的活动外键

The has_one association would be used if you have a foreign key on the target table pointing back to your Campaign.

例如，您的表将有

标签：ID，标签，campaign_id 类别：编号，类别，campaign_id

和将有一个 belongs_to的：他们两个活动的关联。在这种情况下，你必须使用 HAS_ONE：标签和 HAS_ONE：类，但你不能使用一个普通的目标在这一点上。

and would have a belongs_to :campaign association on both of them. In this case, you'd have to use has_one :tag and has_one :category, but you couldn't use a generic target at this point.

这是否更有意义？

修改

由于 target_id 和 TARGET_TYPE 是有效的外键到另一个表，你的广告系列属于其中之一。我可以看到你的困惑的写法，因为在逻辑上的广告系列的容器。我想你可以把它看成是广告系列有一个单一的目标，这是一个标签或容器，因此它属于一个标签或容器。

Since target_id and target_type are effectively foreign keys to another table, your Campaign belongs to one of them. I can see your confusion with the wording because logically the Campaign is the container. I guess you can think of it as Campaign has a single target, and that's a Tag or a Container, therefore it belongs in a Tag or Container.

在 HAS_ONE 是说的关系在目标类中定义的方法。例如，标签将通过一个 HAS_ONE 的关系，因为没有什么标签上的类相关联的运动，标识的关联。在这种情况下，你必须

The has_one is the way of saying the relationship is defined on the target class. For example, a Tag would have be associated to the campaign through a has_one relationship since there's nothing on the tag class that identifies the association. In this case, you'd have

class Tag < ActiveRecord::Base
  has_one :campaign, :as => :target
end

和同样为类别。在这里，：为关键字告诉导轨其关联涉及回本标签。 Rails的不知道怎么算出这个前期，因为有这个名字没有关联标记在广告系列。

and likewise for a Category. Here, the :as keyword is telling rails which association relates back to this Tag. Rails doesn't know how to figure this out upfront because there's no association with the name tag on the Campaign.

另外两个选项，可以提供进一步的混乱是源和 SOURCE_TYPE 选项。这些选项只用在：通过的关系，在这里你实际上是通过另一个表加入该协会。该文档可能更好地描述它，但源定义的关联名称， SOURCE_TYPE 被用在该协会是多态。他们只需要使用当目标协会（在：通过类）都有一个名字，是不是显而易见的 - 像上面用目标和标签 - 我们需要告诉Rails要使用哪一个

The other two options that may provide further confusion are the source and source_type options. These are only used in :through relationships, where you're actually joining the association through another table. The docs probably describe it better, but the source defines the association name, and source_type is used where that association is polymorphic. They only need to be used when the target association (on the :through class) has a name that isn't obvious -- like the case above with target andTag -- and we need to tell rails which one to use.

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