Validating only one attribute using ActiveRecord::Base#valid? - ruby-on-rails

Question

I'm looking for a way to use ActiveRecord::Base#valid? on only one attribute. Consider the following example, inspired by RailsGuides:
class Product < ActiveRecord::Base
belongs_to :company
validates :legacy_code, format: { with: /\A[a-zA-Z]+\z/ }
validates :name, uniqueness: { scope: :company }
end
Calling Product#valid? will trigger a SQL query because of the name validation:
Product.new(legacy_code: "helloworld", company: c).valid?
Product Exists (0.3ms) SELECT 1 AS one FROM "products" WHERE ("products"."name" IS NULL AND "products"."company_id" = 1) LIMIT 1
=> true
Now, I'm only looking to validate the legacy_code attribute:
Product.new(legacy_code: "helloworld").valid?
Product Exists (0.2ms) SELECT 1 AS one FROM "products" WHERE ("products"."name" IS NULL AND "products"."company_id" IS NULL) LIMIT 1
=> true
See the issue? I'd love to use something like Product#valid?(:legacy_code) and avoid the query that's trying to validate an attribute I don't care about.
So far, my solution is to use a Product#valid_legacy_code? method that I can call independently, and call this method as well in the validation declarations on my model.

Answer 1

I ended up writing a gem for that: https://github.com/KevinBongart/valid_attribute
# Test only one attribute:
product.valid_attribute?(:company) # => true
product.valid_attribute?(:name) # => true
product.valid_attribute?(:legacy_code) # => false
# Test several attributes at once, like a boss:
product.valid_attribute?(:company, :name) # => true
product.valid_attribute?(:company, :name, :legacy_code) # => false
# Wow, you can even filter down to a specific validator:
product.valid_attribute?(name: :format) # => true
product.valid_attribute?(name: [:format, :uniqueness]) # => true
product.valid_attribute?(name: :format, company: :presence) # => true