CarrierWave attributes that are not in the database is always equal to nil

Question

I am use Rails 4.0.0 with CarrierWave gem. Why are the attributes that are not in the database is always equal to nil? It is only within the file PostUploader. Ultimately, the data arrives. How to make sure that these attributes are available in the file PostUploader?

class PostUploader < CarrierWave::Uploader::Base
...
  version :thumb do
    process :crop
  end

  def crop
    model.image_crop # => nil
  end
...
end

model:

validates :name, presence: true
mount_uploader :image, PostUploader
attr_accessor :crop_x, :crop_y, :crop_w, :crop_h

controller:

def create
   @post = Post.new(post_params)
   ...
end

def post_params
  params.require(:post).permit(:name, :image, :crop_x, :crop_y, :crop_w, :crop_h)
end

post_params {"name"=>"trololo", "image"=>#, @original_filename="large (3).jpg", @content_type="image/jpeg", @headers="Content-Disposition: form-data; name=\"post[image]\"; filename=\"large (3).jpg\"\r\nContent-Type: image/jpeg\r\n">, "crop_x"=>"0", "crop_y"=>"0", "crop_w"=>"100", "crop_h"=>"200"}

model object in PostUploader:

Post id: nil, name: "trololo", image: nil, created_at: nil, updated_at: nil

and

model.crop_x && model.crop_w always => nil

https://github.com/CandyDandy/Realty/tree/development This project.

Answer 1

I think the reason(based upon your code ) for that is the way assignment are working in tandem inside rails and carrierwave to explain in detail please observe the example below

class A
  attr_accessor :abuse_word,:word
  
  def initialize(abuse_word,word)
    self.word = word
    self.abuse_word = abuse_word
  end
  
  def word=(word)
    puts "Abuse word isnt set yet ...."
    puts "This will be nil => #{self.abuse_word}"
    @word = word
  end
end  

O/p for the program is Like this

a1 = A.new("BAD","GOOD")
 => Abuse word isnt set yet ....
 => This will be nil => 
# But when you do this
a1.abuse_word
  => "BAD"

Now you can imagine something like this happening internally here what I meant

Considering this is your hash

{"name"=>"trololo", "image"=>#, @original_filename="large (3).jpg", @content_type="image/jpeg", @headers="Content-Disposition: form-data; name=\"post[image]\"; filename=\"large (3).jpg\"\r\nContent-Type: image/jpeg\r\n">, "crop_x"=>"0", "crop_y"=>"0", "crop_w"=>"100", "crop_h"=>"200"}

No mind you image= (i.e your uploader_column= setter attributes is overridden by Carrierwave which internally call the processor which you have define i.e crop)

Now If you check the rails,rails does an assign_attributes based upon the hash passed to it check over here

Now when rails does this (by parsing your params)

image=[Value obtain from hash] this invoke the method define by carrierave which internally call the

processor crop and hence you get the desired result as crop_x && crop_w always set to nil because the rails hasn't finish with the assignment of image= and is yet to assign crop_x and crop_w because in hash above they are after in the image key

So

public_send("crop_x=",[desired_value]) public_send("crop_w=",[desired_value])

is not been evaluate yet when your code reached to processor to process the image hence when evaluating in processor crop you get there value as nil

SOLUTION :

I suggest you do something like this in your controller

p1 = Post.new(post_params.except("image"))
p1.image = post_params.delete("image")
p1.save

Or else(I wont suggest this) make sure somehow make sure the crop_x,crop_w are prior to image key in the post_params hash so your hash would look something like this

{"name"=>"trololo","crop_x"=>"0", "crop_y"=>"0", "crop_w"=>"100", "crop_h"=>"200", "image"=>#, @original_filename="large (3).jpg", @content_type="image/jpeg", @headers="Content-Disposition: form-data; name=\"post[image]\"; filename=\"large (3).jpg\"\r\nContent-Type: image/jpeg\r\n">}

You can clearly identify the difference between the two

Hope this help