@alecslupu I don't think it can be solved in the multiple_attachment_methods.rb because it is meant for multiple attachments. In this case we are trying to add a single attachment.

For a quick fix how you can test with the proposals:

1. Implement the changes to the _form.html.erb described at Single attachment with title does work #13792
2. Change this line:

   decidim/decidim-proposals/app/forms/decidim/proposals/proposal_form.rb

   Line 24 in e9e4980

   attachments_attribute :documents

   
   to:

      attribute :documents, Integer
      attribute :add_documents, Hash

1. Change this line:

   decidim/decidim-core/app/commands/decidim/multiple_attachments_methods.rb

   Line 9 in e9e4980

   @form.add_documents.compact_blank.each do |attachment|

   
   to:

      [@form.add_documents].each do |attachment|

1. Change this line:

   decidim/decidim-core/app/commands/decidim/multiple_attachments_methods.rb

   Line 45 in e9e4980

   @form.documents.each do |document|

   
   to:

      [@form.documents].compact.each do |document|

1. Change this line:

   decidim/decidim-core/app/commands/decidim/multiple_attachments_methods.rb

   Line 54 in e9e4980

   @form.documents << document

   
   to:

        @form.documents = document

If these changes were implemented to the multiple_attachment_methods.rb, it would break multiple attachments which is not desired.

Single attachment needs to be handled differently than multiple attachments. Otherwise I would have suggested changing Decidim::MultipleAttachmentsMethods to Decidim::AttachmentMethods but that does not work in this case as the attribute name in that module is hard coded to attachment and it would require more changes to change that.

@alecslupu I don't think it can be solved in the multiple_attachment_methods.rb because it is meant for multiple attachments. In this case we are trying to add a single attachment.
@ahukkanen I understand ... But is there any way of guarding this to avoid this kind of error in the future ?

@ahukkanen I understand ... But is there any way of guarding this to avoid this kind of error in the future ?

It would be refactoring the Decidim::AttachmentMethods to support any attribute name. Now it only supports attachment as the attribute name and also does not support multiple single file attributes.

Also Decidim::MultipleAttachmentsMethods assumes the attribute name on the form is always documents, which might not be always the case. I think the refactor should apply to both of these.

In the actual case where this was noticed (ideas module), the logic for handling the attachments during form submission is customized for the particular case. Of course, it would be nice if we could apply the logic from the core.