Adding File Upload Caching for File Attachments · Wiki · Gateways / awesim-documentation

Migrations

First we need to create a migration to add the file upload to our Simulation table:

rails generate paperclip <ModelName> <FileName>
#rails generate paperclip container myfile

Then we need to apply this migration:
```
rake db:migrate
```

Model

In the model (app/model/container.rb) we first add the common block of code which will need to be added for each individual file upload you want to handle (replace every occurrence of myfile with what you chose):

class Container < ActiveRecord::Base
  attr_accessor :myfile_cache
  attr_accessor :myfile_cache_name
  has_attached_file :myfile
  do_not_validate_attachment_file_type :myfile
  validates_presence_of :myfile
end

Then we add caching methods that will apply to all file uploads you add:

class Container < ActiveRecord::Base
  ...

  # Creates a cache file and sets the appropriate cache file attributes from
  # the file currently staged in `:myfile`
  def myfile_set_cache
    myfile_rm_cache
    self.myfile_cache = File.join Dir.tmpdir, "#{SecureRandom.urlsafe_base64}.cache"
    FileUtils.ln myfile.staged_path, myfile_cache
    self.myfile_cache_name = myfile_file_name
  end

  # Deletes the cached file and resets the appropriate cache file attributes
  def myfile_rm_cache
    FileUtils.rm myfile_cache if File.exist?(myfile_cache.to_s)
    self.myfile_cache = nil
    self.myfile_cache_name = nil
  end
end

If you add another file upload in the future, you will copy the given methods and replace the myfile occurrence with the name of the new file.

We then add the callbacks that handle the cached file during various user requests:

class Container < ActiveRecord::Base
  ...

  # Cache file if it is staged otherwise assign the file to the cached file
  before_validation do
    if myfile.staged?
      myfile_set_cache
    elsif File.exist?(myfile_cache.to_s)
      self.myfile = File.new myfile_cache
      self.myfile.instance_write(:file_name, myfile_cache_name)
    end
  end

  # Clean up cache file after we successfully save the file
  after_save do
    myfile_rm_cache
  end
end

If you add a new file upload, don't copy the callbacks. Instead copy the code inside the callback and replace all occurrences of myfile with your file name.

Finally we modify the copy method to properly copy files when we copy simulations:

class Container < ActiveRecord::Base
  ...

  # Make copy of workflow
  def copy
    new_container = self.dup
    new_container.myfile = self.myfile  # make copy of file
    new_container.myfile_set_cache      # cache this copy of the file
    new_container
  end
end

If you add another file upload, just copy the lines with myfile occurrence.

Confirm you renamed all occurrences of myfile to the name of the file you chose when using the Paperclip generator

Views

Show View

Add the file link to the show.html.erb file for the appropriate Simulation:

<p>
  <strong>Myfile:</strong>
  <%= link_to @container.myfile_file_name, @container.myfile.url %>
</p>

Form View

Add the file to the form in _form.html.erb for easy file uploading:

<%= bootstrap_form_for(container) do |f| %>
  ...

  <%= f.hidden_field :myfile_cache %>
  <%= f.hidden_field :myfile_cache_name %>
  <%= f.file_field :myfile, label: "Myfile (#{f.object.myfile_cache_name || f.object.myfile_file_name})" %>

  ...
<% end %>