CODEWITHSUNDEEP
ruby-on-railsactiverecord
Sara Fuerst
Sara Fuerst

Reputation: 6098

Missing Attribute Error

I'm working with Rails, and when setting up some tests I encountered: 

ActiveModel::MissingAttributeError:
can't write unknown attribute `group_id`

I'm guessing the issue is in my relations. I have 

class Group < ActiveRecord::Base
    has_many :transactions
    has_many :users
end

And

class Transaction < ActiveRecord::Base
    belongs_to :group 
    belongs_to :user
end

And lastly, 

class User < ActiveRecord::Base
    belongs_to :group
    has_many :transactions
end

I saw that someone had the same error because they were using has_one rather than belongs_to and needed to add an ID column to their DB. I'm using belongs_to though, so I don't think that's what I need? Any ideas?

Upvotes: 1

Views: 4926

Answers (2)

Richard Peck
Richard Peck

Reputation: 76774

Looks like you don't have the group_id column in your db.

You must remember that Rails is built on top of a relational database, which means that you can access "related" data by referencing a foreign_key.

When setting up a belongs_to / has_many association, the belongs_to table needs to have the appropriate foreign key (in your case group_id):

enter image description here

Your error doesn't state which model you're receiving the exception for; I would hazard a guess that it's User or Transaction.

--

To fix it, I would recommend creating a migration to add the group_id attribute to the appropriate model:

$ rails g migration AddGroupId

#db/migrate/add_group_id____________.rb
class AddGroupID < ActiveRecord::Migration
   def change
      add_column :users, :group_id, :integer
   end
end

$ rake db:migrate

Upvotes: 1

ChiefRockaChris
ChiefRockaChris

Reputation: 653

Unless you created the model you are referring to with a migration that had references, you will still need a migration in your database. An easy way to check if the database has one is to visit your some_project_root/db/schema.rb. If you don't see a the field you want there then you will have to generate one. The way you would do so is to run a rails g migration AddXidToY x_id:integer . It should set a field up for the id in the table you want.

Upvotes: 1

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