ActiveStorage - 上传后获取图像尺寸

Question

我正在使用Rails + ActiveStorage上传图片文件，上传后想把宽高保存在数据库中。但是，我无法在任何地方找到任何此类示例。

这是我从各种 API 文档中拼凑出来的内容，但最终出现了这个错误：private method 'open' called for #<String:0x00007f9480610118>。将 blob 替换为 image.file 会导致 rails 记录 "Skipping image analysis because ImageMagick doesn't support the file" (https://github.com/rails/rails/blob/master/activestorage/lib/active_storage/analyzer/image_analyzer.rb#L39).

代码：

class Image < ApplicationRecord
  after_commit { |image| set_dimensions image }

  has_one_attached :file

  def set_dimensions(image)
    if (image.file.attached?)
      blob = image.file.download

      # error: private method `open' called for #<String:0x00007f9480610118>
      meta = ActiveStorage::Analyzer::ImageAnalyzer.new(blob).metadata
    end
  end
end

这种方法也有问题，因为 after_commit 也会在销毁时调用。

TLDR:上传后是否有"proper"立即获取图像元数据的方法？

Answer 1

我认为您可以在更新前从 javascript 获取维度，然后 post 这些数据进入控制器。你可以看看： Check image width and height before upload with Javascript

Answer 2

回答自己的问题：我原来的解决方案很接近，但需要安装 ImageMagick（不是，错误消息也没有指出这一点）。这是我的最终代码：

class Image < ApplicationRecord
  attr_accessor :skip_set_dimensions
  after_commit ({unless: :skip_set_dimensions}) { |image| set_dimensions image }

  has_one_attached :file

  def set_dimensions(image)
    if (Image.exists?(image.id))
      if (image.file.attached?)
        meta = ActiveStorage::Analyzer::ImageAnalyzer.new(image.file).metadata

        image.width = meta[:width]
        image.height = meta[:height]
      else
        image.width = 0
        image.height = 0
      end

      image.skip_set_dimensions = true
      image.save!
    end
  end
end

我还使用 this technique 跳过 save! 上的回调，防止无限循环。

Answer 3

Rails 内置解决方案

根据ActiveStorage Overview Guild there is already existing solution image.file.analyze and image.file.analyze_later (docs ) which uses ActiveStorage::Analyzer::ImageAnalyzer

根据#analyze docs：

New blobs are automatically and asynchronously analyzed via analyze_later when they're attached for the first time.

这意味着您可以使用

访问您的图像尺寸

image.file.metadata
#=> {"identified"=>true, "width"=>2448, "height"=>3264, "analyzed"=>true}

image.file.metadata['width']
image.file.metadata['height']

所以你的模型看起来像：

class Image < ApplicationRecord
  has_one_attached :file

  def height
    file.metadata['height']
  end

  def width
    file.metadata['width']
  end
end

对于 90% 的常规情况，您都擅长此操作

但是：问题是这是“异步分析”（#analyze_later）意味着您不会在上传后立即存储元数据

image.save!
image.file.metadata
#=> {"identified"=>true}
image.file.analyzed?
# => nil

# .... after ActiveJob for analyze_later finish
image.reload
image.file.analyzed?
# => true
#=> {"identified"=>true, "width"=>2448, "height"=>3264, "analyzed"=>true}

这意味着如果您需要实时访问 width/height（例如 API 响应新上传文件的尺寸），您可能需要

class Image < ApplicationRecord
  has_one_attached :file
  after_commit :save_dimensions_now

  def height
    file.metadata['height']
  end

  def width
    file.metadata['width']
  end

  private
  def save_dimensions_now
    file.analyze if file.attached?
  end
end

Note: there is a good reason why this is done async in a Job. Responses of your request will be slightly slower due to this extra code execution needs to happen. So you need to have a good reason to "save dimensions now"

Mirror of this solution can be found at How to store Image Width Height in Rails ActiveStorage

DIY 解决方案

recommendation: don't do it, rely on existing Vanilla Rails solution

需要更新附件的模型

会起作用。这是没有 skip_set_dimensions attr_accessor

的相同解决方案的重写

class Image < ApplicationRecord
  after_commit :set_dimensions

  has_one_attached :file

  private

  def set_dimensions
    if (file.attached?)
      meta = ActiveStorage::Analyzer::ImageAnalyzer.new(file).metadata
      height = meta[:height]
      width  = meta[:width]
    else
      height = 0
      width  = 0
    end

    update_columns(width: width, height: height) # this will save to DB without Rails callbacks
  end
end

update_columns docs

不需要更新附件的机型

您可能正在创建要存储文件附件并且永远不再更新它的模型。（因此，如果您需要更新附件，您只需创建新的模型记录并删除旧的）

在那种情况下，代码甚至更流畅：

class Image < ApplicationRecord
  after_commit :set_dimensions, on: :create

  has_one_attached :file

  private

  def set_dimensions
    meta = ActiveStorage::Analyzer::ImageAnalyzer.new(file).metadata
    self.height = meta[:height] || 0
    self.width  = meta[:width] || 0
    save!
  end
end

您可能希望在保存之前验证附件是否存在。您可以使用 active_storage_validations gem

class Image < ApplicationRecord
  after_commit :set_dimensions, on: :create

  has_one_attached :file

  # validations by active_storage_validations
  validates :file, attached: true,
    size: { less_than: 12.megabytes , message: 'image too large' },
    content_type: { in: ['image/png', 'image/jpg', 'image/jpeg'], message: 'needs to be an PNG or JPEG image' }

  private

  def set_dimensions
    meta = ActiveStorage::Analyzer::ImageAnalyzer.new(file).metadata
    self.height = meta[:height] || 0
    self.width  = meta[:width] || 0
    save!
  end
end

测试

require 'rails_helper'
RSpec.describe Image, type: :model do
  let(:image) { build :image, file: image_file }

  context 'when trying to upload jpg' do
    let(:image_file) { FilesTestHelper.jpg } # https://blog.eq8.eu/til/factory-bot-trait-for-active-storange-has_attached.html

    it do
      expect { image.save }.to change { image.height }.from(nil).to(35)
    end

    it do
      expect { image.save }.to change { image.width }.from(nil).to(37)
    end

    it 'on update it should not cause infinitte loop' do
      image.save! # creates
      image.rotation = 90 # whatever change, some random property on Image model
      image.save! # updates
      # no stack ofverflow happens => good
    end
  end

  context 'when trying to upload pdf' do
    let(:image_file) { FilesTestHelper.pdf } # https://blog.eq8.eu/til/factory-bot-trait-for-active-storange-has_attached.html

    it do
      expect { image.save }.not_to change { image.height }
    end
  end
end

How FilesTestHelper.jpg work is explained in article attaching Active Storange to Factory Bot

ActiveStorage - 上传后获取图像尺寸

ActiveStorage - get image dimensions after upload

ruby-on-rails

rails-activestorage

Rails 内置解决方案

DIY 解决方案

需要更新附件的模型

不需要更新附件的机型