Rails 5.2 Active Storage 添加自定义属性 [英] Rails 5.2 Active Storage add custom attributes

问题描述

我有一个带附件的模型:

I have a model with attachments:

class Project < ApplicationRecord
  has_many_attached :images
end

当我附加并保存图像时，我还想保存附加的图像的附加自定义属性 - display_order(整数).我想用它对附加的图像进行排序，并按照我在此自定义属性中指定的顺序显示它们.我已经查看了 #attach 方法以及 ActiveStorage::Blob 模型的 ActiveStorage 源代码，但似乎没有内置方法来传递一些自定义元数据.

When I attach and save the image I also want to save an additional custom attribute - display_order (integer) with the attached image. I want to use it to sort the attached images and display them in the order I specified in this custom attribute. I've reviewed ActiveStorage source code for #attach method as well as ActiveStorage::Blob model but it looks like there is no built in method to pass some custom metadata.

我想知道，用 ActiveStorage 解决这个问题的惯用方法是什么?过去，我通常只向表示我的附件的 ActiveRecord 模型添加一个 display_order 属性，然后简单地将它与 .order(display_order: :asc) 查询一起使用.

I wonder, what's the idiomatic way to solve this problem with ActiveStorage? In the past I would usually just add a display_order attribute to the ActiveRecord model which represents my attachment and then simply use it with .order(display_order: :asc) query.

推荐答案

如果您需要为每个图像存储额外的数据并根据该数据执行查询，我建议提取一个 Image 模型包装附加的file:

If you need to store additional data with each image and perform queries based on that data, I’d recommend extracting an Image model that wraps an attached file:

# app/models/project.rb
class Project < ApplicationRecord
  has_many :images, dependent: :destroy
end

# app/models/image.rb
class Image < ApplicationRecord
  belongs_to :project

  has_one_attached :file
  delegate_missing_to :file

  scope :positioned, -> { order(position: :asc) }
end

<%# app/views/projects/show.html.erb %>
<% @project.images.positioned.each do |image| %>
  <%= image_tag image %>
<% end %>

请注意，上面的示例视图会导致对具有 N 个图像的项目进行 2N+1 次查询(对项目图像进行一次查询，对每个图像的 ActiveStorage::Attachment 记录进行一次查询，对每个附加 ActiveStorage::Blob).为了清楚起见，我特意避免优化查询数量.

Note that the example view above causes 2N+1 queries for a project with N images (one query for the project’s images, another for each image’s ActiveStorage::Attachment record, and one more for each attached ActiveStorage::Blob). I deliberately avoided optimizing the number of queries for clarity’s sake.

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