Rails 4 strong parameters param not found error with carrierwave

Question

I'm having trouble with carrierwave and rails 4 strong parameters. I have a very simple model with a carrier wave upload button. I'd like to show an error message if someone submits the upload form without choosing a file to upload.

Right now, I get a param not found:photo error with this message:

  # Never trust parameters from the scary internet, only allow the white list through.
    def photo_params
      params.require(:photo).permit(:image)
    end

This error is happening because Rails 4's strong parameters is requiring that the image parameter be present to submit the form, but it's not there because the user hasn't selected an image.

I can't figure out a way to work around this and have it redirect to the same action and display an error message.

Is there a way to do this with strong parameters?

Here's the development log when I try to use the form without a photo selected: https://gist.github.com/leemcalilly/09b6166ce1af6ca6c833

And here's the development log when I choose a photo and it uploads successfully: https://gist.github.com/leemcalilly/1f1e584f56aef15e7af1

Other relevant files: * models/photo.rb - https://gist.github.com/leemcalilly/95c54a5df4e4ee6518da * controllers/photos_controller.rb - https://gist.github.com/leemcalilly/c0723e6dc5478b0f914d * uploaders/image_uploader.rb - https://gist.github.com/leemcalilly/5e43f6524734991773ae * views/photos/index.html.erb - https://gist.github.com/leemcalilly/a8c4c808e5e8a802933b * views/photos/_form.html.erb - https://gist.github.com/leemcalilly/cd0fd518c1b47d9bfb62 * initializers/carrierwaver.rb - https://gist.github.com/leemcalilly/49e04fa1dda891dd108b

Answer 1

The rails guides provides the solution. Use the fetch method in the same way as the require method. Note a second argument: it supplies the default value. So, if the params[:photo] would not be found, the default value (an empty hash, as of the example below) will be returned:

params.fetch(:photo, {})