getting undefined method when trying to call method created in model - ruby-on-rails

Question

I am writing a hacker news clone in rails to learn the framework and encountered a problem calling helper methods within a model:
class User < ActiveRecord::Base
has_secure_password validations: false
has_many :posts
validates :name,
presence: { message: username_error_message },
uniqueness: { case_sensitive: false, message: username_error_message },
length: { minimum: 2, maximum: 15, message: username_error_message }
validates :password,
presence: { message: password_error_message },
length: { minimum: 4, message: password_error_message }
private
def username_error_message
"Usernames can only contain letters, digits, dashes and underscores, and should be between 2 and 15 characters long. Please choose another."
end
def password_error_message
"Passwords should be a least 4 characters long. Please choose another."
end
end
I get the following error (Rails 4):
undefined local variable or method `username_error_message' for #<Class:XXX>

Answer 1

You can use constants for the repeated error messages and it will work.
class User < ActiveRecord::Base
has_secure_password validations: false
has_many :posts
USERNAME_ERROR_MESSAGE = "Usernames can only contain letters, digits, dashes and underscores, and should be between 2 and 15 characters long. Please choose another."
PASSWORD_ERROR_MESSAGE = "Passwords should be a least 4 characters long. Please choose another."
validates :name,
presence: { message: USERNAME_ERROR_MESSAGE },
uniqueness: { case_sensitive: false, message: USERNAME_ERROR_MESSAGE },
length: { minimum: 2, maximum: 15, message: USERNAME_ERROR_MESSAGE }
validates :password,
presence: { message: PASSWORD_ERROR_MESSAGE },
length: { minimum: 4, message: PASSWORD_ERROR_MESSAGE }
end
Also, there is a little problem: the error message will be repeated if more than one validation condition fails for every field. One solution is to write a custom validation method, as can be seen here: http://guides.rubyonrails.org/active_record_validations.html#custom-methods

Answer 2

Try using class methods instead:
validates :name,
presence: { message: Proc.new { username_error_message } },
uniqueness: { case_sensitive: false, message: Proc.new { username_error_message } },
length: { minimum: 2, maximum: 15, message: Proc.new { username_error_message } }
validates :password,
presence: { message: Proc.new { password_error_message } },
length: { minimum: 4, message: Proc.new { password_error_message } }
private
def self.username_error_message
"Usernames can only contain letters, digits, dashes and underscores, and should be between 2 and 15 characters long. Please choose another."
end
def self.password_error_message
"Passwords should be a least 4 characters long. Please choose another."
end

Answer 3

The fundamental problem is that you're accessing your methods before they are defined. This problem has nothing per se to do with whether they are private, constants, instance methods or class methods.
The methods are being referenced as your User class is being defined. The references exist within a hash constructor {} being passed as a parameter to the method call validates, which means it is getting evaluated at the time validates is called. It's not like you're passing a block to validates that gets evaluated at a later time.
If you move your definitions to before you reference them, it will address this fundamental problem, but it is also true that you are defining them as instance methods and referencing to them as class methods. You need to bring your mode of definition in line with your mode of access (e.g. by defining the methods as class methods).
(Note: There are a myriad of other options available to you for defining and referencing these strings beyond those noted in the other answers, including class variables, class local variables, etc. They vary primarily in terms where and how they can be accessed. You can even use instance variables and methods, although that would be odd in this case, requiring you to instantiate an object in order to reference them. The point is that Ruby is rich with possibilities and it's well worth investigating/understanding them when you have the time.)

Answer 4

Try this
class User < ActiveRecord::Base
has_secure_password validations: false
has_many :posts
validates :name,
presence: { message: self.username_error_message },
uniqueness: { case_sensitive: false, message: self.username_error_message },
length: { minimum: 2, maximum: 15, message: self.username_error_message }
validates :password,
presence: { message: self.password_error_message },
length: { minimum: 4, message: self.password_error_message }
def username_error_message
"Usernames can only contain letters, digits, dashes and underscores, and should be between 2 and 15 characters long. Please choose another."
end
def password_error_message
"Passwords should be a least 4 characters long. Please choose another."
end
end
private :username_error_message, :password_error_message
I just added some "self." before the methods call to give it a context of this instance.
I also changed the private declaration method