ActiveRecord::StatementInvalid PG::UndefinedColumn: ERROR

Question

I am using rails_admin for admin panel. Just change association in Image model

From this

class Image < ApplicationRecord
   belongs_to :user 
   belongs_to :product 
end

to this

class Image < ApplicationRecord
   has_one :user 
   has_one :product 
end

and User model is

class User < ApplicationRecord
   has_many :images,dependent: :destroy
end

Getting this error when I try to edit user from admin panel.From other side it is working fine.

ActiveRecord::StatementInvalid at /user/72/edit

PG::UndefinedColumn: ERROR:  column users.image_id does not exist
LINE 1: SELECT  "users".* FROM "users" WHERE "users"."image_id" = $1...
                                         ^
: SELECT  "users".* FROM "users" WHERE "users"."image_id" = $1 LIMIT $2

Answer 1

Rails has great documentation. The documentation for has_one found here states that "This method should only be used if the other class contains the foreign key" so it is looking for the foreign key of image_id on the user record. You would create this through a migration; please see this stack overflow post for more information on foreign keys and migrations.

But before you go that far, please consider:

• Why would you change the Image relation from belongs_to :user to has_one :user in the first place? To boil down SQL associations and how Rails maps to them, if user has_many :images then images must necessarily belong_to user; they are opposite sides of the relation, with an exception being a has_and_belongs_to_many relation. If A belongs to B, then B has one (or many) of A. I would strongly encourage you to keep the images as having belongs_to relationships, while User and Product can have_many images. To anecdotally explain why this makes sense: a user might have profile pictures of their face, their house, etc. (has_many :images). A product (shoes) might have multiple pictures of the same shoe (has_many :images), but it is very unlikely that a particular picture of a shoe would map to both a user and a product.
• I would strongly encourage you manage images and attachments using a gem like attachinary or paperclip. If you're handling uploaded file attachments, libraries like this will save you headaches down the road when it comes to resizing, image compression, etc. I am sure your direction in trying to change the relation was informed by some of the issues that these gems will solve for you.