渴望加载不同的嵌套多态 [英] Eager load differently nested polymorphic

问题描述

使用 Rails 3.2.我的模型是这样嵌套的:

Using Rails 3.2. My models are nested in such a way:

• 评论 => 可评论(国家或商店)
• 国家 => CountryDay => 商店 => 照片
• 商店 => 照片

我有以下几点:

@reviews = @user.reviews.includes(:user, :reviewable)

通常我们可以通过以下方式包含嵌套多态:

Usually we can include nested polymorphic in such a way:

# this will return errors because :shop is not found in the model Shop (:reviewable is actually :shop)
@reviews = @user.reviews.includes(:user, :reviewable => [:shop])

# this will return errors because :photos is not directly associated to Country
@reviews = @user.reviews.includes(:user, :reviewable => :photos)

还有许多其他变体.我如何解决这个问题，让 ActiveRecord 包含基于其关联的正确模型?

There are many other variants. How do I work around it to have the ActiveRecord includes the correct model based on its association?

推荐答案

我想我刚才也遇到了同样的问题.尝试加载关联时出现 ActiveRecord::EagerLoadPolymorphicError.我的解决方案是将自定义连接语句放在一起，我已将其放入一个范围内以便于使用.

I think I had the same problem just now. I got an ActiveRecord::EagerLoadPolymorphicError when trying to load associations. My solution was to put together a custom join statement which I've put into a scope for easier usage.

未经测试，但这可能会让您前进:

Untested, but this may get you going:

class Review < ActiveRecord::Base
  scope :eagerly_loaded, -> {
    joins('
      INNER JOIN shops 
      ON (reviews.reviewable_type = "Shop" AND reviews.reviewable_id = shops.id)
      INNER JOIN countries 
      ON (reviews.reviewable_type = "Country" reviews.reviewable_id = countries.id)
    ')
  }
end

然后您使用 @user.reviews.eagerly_loaded.确保使用匹配的 .group() 语句以仅获取您需要的语句.

You then use @user.reviews.eagerly_loaded. Make sure to use a matching .group()-statement to only get the ones you need.

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