validate_presence_of fails for Shrine UploadedFile since empty string was introduced

[klaustopher]

This somehow relates to #1223 and #1218, but I think it is also different. Please feel free to close and merge with one of the open issues.

Currently our update to 4.1.0 is blocked because on of our test cases is failing with the new version.

The model is super simple:

class ImageUpload < ApplicationRecord
  include ImageUploader::Attachment.new(:image)
  validates_presence_of :image
end

I have played around a bit and the shrine uploader simply ignores assigning "" to the image attribute:

>> up = FactoryBot.build(:image_upload)
# => #<ImageUpload id: nil, image_data: {"id"=>"a4cd635bb1252991f6c539e3d27220cd.jpg", "storage"=>"cache", "metadata"=>{"filename"=>"image_upload_fixture.jpg", "size"=>12183, "mime_type"=>"image/jpeg", "width"=>100, "height"=>200}}, created_at: nil, updated_at: nil>

>> up.image
# => #<ImageUploader::UploadedFile:0x00007fb961af2bf8 @data={"id"=>"a4cd635bb1252991f6c539e3d27220cd.jpg", "storage"=>"cache", "metadata"=>{"filename"=>"image_upload_fixture.jpg", "size"=>12183, "mime_type"=>"image/jpeg", "width"=>100, "height"=>200}}>

>> up.image = ''
# => ""

>> up.image
# => #<ImageUploader::UploadedFile:0x00007fb961afaf88 @data={"id"=>"a4cd635bb1252991f6c539e3d27220cd.jpg", "storage"=>"cache", "metadata"=>{"filename"=>"image_upload_fixture.jpg", "size"=>12183, "mime_type"=>"image/jpeg", "width"=>100, "height"=>200}}>

>> up.image = nil
# => nil

>> up.image
# => nil

Checking all the conditions:

>> ImageUpload.reflect_on_association(:image)
# => nil

>> ImageUpload.attribute_types['image']
# => #<ActiveModel::Type::Value:0x00007fd607362d58 @precision=nil, @scale=nil, @limit=nil>

>> ImageUpload.attribute_types['image'].respond_to?(:coder)
# => false

Shrine seems to use an unspecified ActiveModel::Type class.

---

For now, we have added a few custom tests instead of validate_presence_of for the field, but maybe it's possible to make the empty string check optional with a modifier?

[mcmire]

Thanks for the report! I have a branch in the works that should fix this issue, but I'll leave this open in the meantime.

[vitalinfo]

the same problem with serializable fields, like
serialize :data, Array

got an exception:

     Failure/Error: it { is_expected.to validate_presence_of :data }
     
     ActiveRecord::SerializationTypeMismatch:
       can't serialize `data`: was supposed to be a Array, but was a String. -- ""
....

[benedikt]

I'm running into similar problems with attributes (or rather methods) that get validated but are not handling strings but objects. In theory I could make all setters handle empty strings, but it feels like the wrong path.

[mcmire]

@klaustopher @vitalinfo @benedikt Hey, I just pushed up a branch, fix-presence-validation-for-activemodel, that should fix this issue. Can you temporarily switch to it in your Gemfile and see if makes your tests pass?

[benedikt]

@mcmire Yes, that works. Thanks a lot for your efforts, Elliot!

[klaustopher]

Tested revision 11f4483 and it works fine with Shrine.

[mcmire]

Fixed in v4.1.1.