Rails Validation with two attributes of a variable - ruby-on-rails

Question

I really need your help, because I can't find a solution on my own since 2 hours. I tried many different approaches, but I just don't get how I can validate an attribute of a variable by using another attribute as a condition.
This was my last try:
class User < ApplicationRecord
validates :admin, absence: true,
if: ["student?", :email]
def student?(user)
user.email.include? 'stud'
end
end
I want to validate, that a user with the attribute "admin" can't have an email address, which includes 'stud'. Even better would be a validation, that 'stud' users can't be admin.
When I run db:seed I get this error, which stays if I put the 'stud' in brackets:
rails aborted!
ArgumentError: wrong number of arguments (given 0, expected 1)
/home/studi/Bachelorarbeitsapp/sample_app/app/models/user.rb:22:in `student?'
Please have a look at this issue!
I am willing to share any other code, which is necessary to solve the problem. Thanks!
Here is the full helper code:
class User < ApplicationRecord
has_many :preferences, dependent: :destroy
accepts_nested_attributes_for :preferences
attr_accessor :remember_token, :activation_token, :reset_token
before_save :downcase_email
before_create :create_activation_digest
has_secure_password
validates :name, presence: true, length: { maximum: 50 }
VALID_EMAIL_REGEX = /\A[\w+\-.]+#(stud.uni-hannover.de|wiwi.uni-hannover.de)+\z/i
validates :email, presence: true, length: { maximum: 255 }, format: { with: VALID_EMAIL_REGEX }, uniqueness: {case_sensitive: false}
validates :password, presence: true, length: { minimum: 6 }, allow_nil: true
validates :mat_number, presence: true, length: { minimum: 7, maximum: 8 }, numericality: { only_integer: true }
validates :admin, absence: true,
if: ["student?", :email]
def student?(user)
user.email.include? 'stud'
end
validates :ects, numericality: { greater_than_or_equal_to: 0, less_than_or_equal_to: 170, only_integer: true }, allow_nil: true
validates :grade_avg, numericality: { greater_than_or_equal_to: 1, less_than_or_equal_to: 4 }, allow_nil: true
# Returns the hash digest of the given string.
def User.digest(string)
cost = ActiveModel::SecurePassword.min_cost ? BCrypt::Engine::MIN_COST :
BCrypt::Engine.cost
BCrypt::Password.create(string, cost: cost)
end
# Returns a random token
def User.new_token
SecureRandom.urlsafe_base64
end
# Remembers a user in the database for use in persistent sessions
def remember
self.remember_token = User.new_token
update_attribute(:remember_digest, User.digest(remember_token))
end
# Returns true if the given token matches the digest.
def authenticated?(attribute, token)
digest = send("#{attribute}_digest")
return false if digest.nil?
BCrypt::Password.new(digest).is_password?(token)
end
# Forgets a user.
def forget
update_attribute(:remember_digest, nil)
end
# Activates an account.
def activate
update_columns(activated: true, activated_at: Time.zone.now)
end
# Sends activation email.
def send_activation_email
UserMailer.account_activation(self).deliver_now
end
# Sets the password reset attributes.
def create_reset_digest
self.reset_token = User.new_token
update_columns(reset_digest: User.digest(reset_token), reset_sent_at: Time.zone.now)
end
# Sends password reset email.
def send_password_reset_email
UserMailer.password_reset(self).deliver_now
end
# Returns true if a password reset has expired.
def password_reset_expired?
reset_sent_at < 2.hours.ago
end
private
# Converts email to all lower-case.
def downcase_email
self.email = email.downcase
end
# Creates and assigns the activation token and digest.
def create_activation_digest
self.activation_token = User.new_token
self.activation_digest = User.digest(activation_token)
end
end

Answer 1

Based on the Active Record Validations Guide section 6.2 Custom Methods, it seems like you should be able to do something like:
class User < ApplicationRecord
validate :admin_cant_be_student
def admin_cant_be_student
if admin and email.include?('stud')
errors.add(:admin, "can't have a student email address")
end
end
end

Answer 2

You don’t need a custom validation:
Could use validates_exclusion_of
validates_exclusion_of :email, in: %w( stud ), if: -> { |user| user.email.include? “admin” }, message: “admins can’t have stud in email”
validates_exclusion_of :email, in: %w( admin ), if: -> { |user|user.email.include? “stud” }, message: “students can’t have admin in email”