Rails custom validate - uniqueness of a property across models - ruby-on-rails

Question

I'm stuck at defining a custom validation method that's purpose is to verify uniqueness of a property across two models
I realize this is bad code, but i wanted to get the test passing before refactor
here is a model with the custom validation to check another model property, error undefined local variable or method `params' (be gentle I'm still trying to figure out RoR)
class Widget < ActiveRecord::Base
include Slugable
validates :name, presence: true
validate :uniqueness_of_a_slug_across_models
def uniqueness_of_a_slug_across_models
#sprocket = Sprocket.where(slug: params[:widget_slug]).first
if #sprocket.present?
errors.add(:uniqueness_of_a_slug_across_models, "can't be shared slug")
end
end
end

Answer 1

You don't have access to params in a model. It belongs to controller and view. What you could do is to call custom method in widgets controller (instead of regular save) in order to pass params to a model:
class WidgetsController < ActionController::Base
def create
#widget = Widget.new(widget_params)
if #widget.save_with_slug_validation(params)
redirect_to widgets_path
else
render :new
end
end
end
and define it:
class Widget < ActiveRecord::Base
# ...
def save_with_slug_validation(params)
sprocket = Sprocket.find_by(slug: params[:widget_slug])
if sprocket
errors.add(:uniqueness_of_a_slug_across_models, "can't be shared slug")
end
save
end
end
I didn't test it but it should work.
P.S. Rails 4 style is used.
UPD
I should have tested it, sorry. Please use another approach.
Widgets controller:
# POST /widgets
# POST /widgets.json
def create
#widget = widget.new(widget_params)
#widget.has_sprocket! if Sprocket.find_by(slug: params[:widget_slug])
respond_to do |format|
if #widget.save
format.html { redirect_to [:admin, #widget], notice: 'widget was successfully created.' }
format.json { render action: 'show', status: :created, location: #widget }
else
format.html { render action: 'new' }
format.json { render json: #widget.errors, status: :unprocessable_entity }
end
end
end
Widget model:
class Widget < ActiveRecord::Base
include Slugable
validates :name, presence: true
validate :uniqueness_of_a_slug_across_models, if: 'has_sprocket?'
def uniqueness_of_a_slug_across_models
errors.add(:uniqueness_of_a_slug_across_models, "can't be shared slug")
end
def has_sprocket!
#has_sprocket = true
end
def has_sprocket?
!!#has_sprocket
end
end
It would be better to move has_sprocket! and has_sprocket? methods and maybe validation itself to Slugable concern.