Module: EchoUploads::TmpFileWriting

Extended by:
ActiveSupport::Concern
Defined in:
lib/echo_uploads/tmp_file_writing.rb

Overview

This comment is current as of Rails 4.2.5.

This module writes temporary EchoUploads::Files on failed attempts to save the main ActiveRecord model. Because ActiveRecord wraps save attempts in transactions, we can’t use after_save callbacks. If we tried, the EchoUploads::Files would be lost upon rollback. Instead, we have to wrap the #save, #create, and #update methods so that the EchoUploads::Files are saved outside the transactions.

Here is the ancestor chain for ActiveRecord::Base, including this module, highest-priority first:

EchoUploads::TmpFileWriting -> ActiveRecord::Transactions -> ActiveRecord::Persistence

Here is the control flow for each of the main persistence methods. (T) denotes that the method wraps all subsequent calls in a transaction.

#save

EchoUploads::TmpFileWriting#save -> ActiveRecord::Transactions#save (T) ->
ActiveRecord::Persistence#save

#create

ActiveRecord::Persistence#create -> EchoUploads::TmpFileWriting#save ->
ActiveRecord::Transactions#save (T) -> ActiveRecord::Persistence#save

#update

EchoUploads::TmpFileWriting#update -> ActiveRecord::Persistence#update (T) -> 
EchoUploads::TmpFileWriting#save -> ActiveRecord::Transactions#save (T) ->
ActiveRecord::Persistence#save

Per the above, #save and #create are easy enough: We just wrap #save. But #update is problematic because it starts its own transaction and then delegates to #save. Because of that outer transaction, we can’t rely on the #save wrapper. Instead, we have to wrap #update. To prevent writing the temp file twice (once in #update and again in #save), #update sets @echo_uploads_persistence_wrapped. This tells the #save wrapper not to write the temp file.

Defined Under Namespace

Modules: ClassMethods

Instance Method Summary collapse

Instance Method Details

#echo_uploads_maybe_write_tmp_file(attr, options) ⇒ Object

On a failed attempt to save (typically due to validation errors), save the file and metadata. Metadata record will be given the temporary flag.



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# File 'lib/echo_uploads/tmp_file_writing.rb', line 49

def echo_uploads_maybe_write_tmp_file(attr, options)
  if (file = send(attr)).present? and errors[attr].empty?
    # A file has been uploaded. Validation failed, but the file itself was valid.
    # Thus, we must persist a temporary file.
    # 
    # It's possible at this point that the record already has a permanent file.
    # That's fine. We'll now have a permanent and a temporary one. The temporary
    # one will replace the permanent one if and when the user resubmits with
    # valid data.
    
    # Construct an array of EchoUploads::File instances. The array might have only
    # one element.
    if options[:multiple]
      mapped_files = send("mapped_#{attr}") ||
        raise('echo_uploads called with :multiple, but :map option was missing')
      metas = mapped_files.map do |mapped_file|
        ::EchoUploads::File.new(
          owner: nil, temporary: true, expires_at: options[:expires].from_now,
          file: mapped_file
        )
      end
    else
      metas = [::EchoUploads::File.new(
        owner: nil, temporary: true, expires_at: options[:expires].from_now,
        file: send(attr)
      )]
    end
    
    # Persist each file. (There might only be one, though.)
    metas.each do |meta|
      meta.persist! attr, options
    end
    
    # Set the attr_tmp_metadata attribute so the form can remember our records.
    send("#{attr}_tmp_metadata=", metas)
  end
end

#echo_uploads_persistence_wrapper ⇒ Object 



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# File 'lib/echo_uploads/tmp_file_writing.rb', line 87

def echo_uploads_persistence_wrapper
  success = yield
  unless success
    self.class.echo_uploads_save_wrapper.each do |attr, options|
      echo_uploads_maybe_write_tmp_file(attr, options)
    end
    if self.class.included_modules.include? ::EchoUploads::Callbacks
      run_callbacks :failed_save
    end
  end
  success
end

#save ⇒ Object 



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# File 'lib/echo_uploads/tmp_file_writing.rb', line 101

def save(*)
  if @echo_uploads_persistence_wrapped
    super
  else
    echo_uploads_persistence_wrapper { super }
  end
end

#update ⇒ Object Also known as: update_attributes 



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# File 'lib/echo_uploads/tmp_file_writing.rb', line 110

def update(*)
  echo_uploads_persistence_wrapper do
    begin
      @echo_uploads_persistence_wrapped = true
      super
    ensure
      @echo_uploads_persistence_wrapped = nil
    end
  end
end