#carrierwave

Here we go: This one has bothered me for two full days now and since there were no suitable stackoverflow answers and carrierwave tutorials didn’t work I thought I’ll post this here. In fact, it’s a pretty trivial problem:

We’re currently rewriting parts of Smaply. We use jCrop in frontend to give users the ability to choose which part of their uploaded picture they want to make the profile image of personas. It looks something like this:

So, when the request comes in from the frontend, it’s basically a multipart-form with four additional values (crop_x, crop_y, crop_w and crop_h) which define the area to be cropped.

Carrierwave offers the possibility to create versions and give them sizes. What it doesn’t suggest however, is a standard way to pass my request params over to those instance methods.

There are several suggested solutions:

 http://stackoverflow.com/questions/21706445/rails-jcrop-rmagick-bootstrap-no-method-error suggests that you should recreate the version after creating the image which really sounds like unnecessary overhead to me and brings problems if you use fog.

http://railscasts.com/episodes/182-cropping-images-revised same suggestion as above. I don’t want to upload, then crop and upload again.

https://medium.com/philosophie-is-thinking/carrierwave-process-parameters-or-makeit800-com-casualty-of-the-zeitgeist-12e80a80d754 suggests to use instance variables in the uploader. TL:DR; IT DOESN’T WORK since a new instance is created as soon as you pass the file param.

http://stackoverflow.com/questions/10631060/how-can-i-pass-arbitrary-user-defined-values-into-a-carrierwave-image-processor works perfectly fine in Rails 3.

At first I fell in love with suggestion number 3, since it felt better to have those instance variables in the Uploader class itself. However this approach just doesn’t work because Carrierwave triggers the upload as soon as you pass in the file param and therefore creates a new instance of the Uploader class where those attributes are obviously nil.

I converted to “puts driven development” mode and added some statements and a byebug marker in order to be able to debug a little better and understand the Carrierwave internals. Here is the log output that catched my attention (I pixelated some swearing of mine):

So, option Number 3 didn’t work either. Back to the basic idea of just adding those instance variables to the model itself as suggested in the last Stackoverflow Link above. But somehow it still didn’t work until I scrolled further down: