Question

我正在rails中编写一个黑客新闻克隆来学习框架，并在模型中遇到调用辅助方法的问题：

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

我收到以下错误（Rails 4）：

undefined local variable or method `username_error_message' for #<Class:XXX>

Answer 1

您可以对重复的错误消息使用常量，它将起作用。

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

此外，还有一个问题：如果每个字段的多个验证条件失败，则会重复出现错误消息。一种解决方案是编写自定义验证方法，如下所示：http://guides.rubyonrails.org/active_record_validations.html#custom-methods

Answer 2

尝试使用类方法：

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

根本问题在于您在定义之前访问方法。这个问题本身没有任何关于它们是私有，常量，实例方法还是类方法的事情。

正在定义您的User类时引用这些方法。引用存在于散列构造函数{}中，作为参数传递给方法调用validates，这意味着在validates被调用时正在评估。这不像是你将一个块传递给validates以后再进行评估。

如果您在之前将定义移动到，那么它将引用它们，它将解决这个基本问题，但您也可以将它们定义为实例方法并将它们作为类方法引用。您需要使您的定义模式符合您的访问模式（例如，将方法定义为类方法）。

（注意：除了其他答案中提到的字符串之外，还有许多其他选项可用于定义和引用这些字符串，包括类变量，类局部变量等。它们主要在于它们在何处以及如何你甚至可以使用实例变量和方法，虽然在这种情况下这很奇怪，需要你实例化一个对象才能引用它们。重点是Ruby有很多可能性，值得研究/理解它们。当你有时间的时候。）

Answer 4

试试这个

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

我刚加了一些“自我”。在方法调用之前给它一个这个实例的上下文。我还改变了私有声明方法

在尝试调用模型中创建的方法时获取未定义的方法

4 个答案: