Rails 3 - 使用 2 个模型和其他警告进行验证？答案

【问题标题】：Rails 3 - Validation with 2 models and additional warnings?Rails 3 - 使用 2 个模型和其他警告进行验证？
【发布时间】：2011-05-13 02:31:36
【问题描述】：

我有两个模型：

讲座
注册

讲座有名额和等候名单。如果有讲座报名，我想确认是否有空位。

为此创建了两个助手：

def availableSeats
  return self.capacity - self.enrollments.confirmedEnrollments.count
end

def waitListAvailable
  return self.waitListCapacity - self.enrollments.waitList.count
end

我想过在注册控制器中进行检查，但它不起作用。

if(@lecture.availableSeats <= 0)
  if(@lecture.waitListAvailable <= 0)
    flash[:error] = "Enrolment not possible as the waiting list is full."
    # interrupt and don't save, but how?
  else
    flash[:warning] = "You are on the waiting list."
    @enrollment.confirmed = nil
  end
else
  @enrollment.confirmed = DateTime.now
end

有什么想法吗？

【问题讨论】：

标签： ruby-on-rails model-view-controller validation

【解决方案1】：

我假设您的注册模型同时定义了被录取的学生和等待名单上的学生。我还假设 Lecture 模型有两个属性 available_seats 和 available_wait_space，并且等候名单以先到先得的方式填充，如果名单已满，学生将被拒绝，但实际座位被确认或拒绝由讲师手动操作。

我当然建议不要在控制器级别做任何事情。这只是模型的工作。

class Enrollment < ActiveRecord::Base
  belongs_to :student
  belongs_to :lecture

  validates_presence_of  :student_id, :lecture_id, :status
  validates_inclusion_of :status, :in => %w[waiting confirmed rejected]
  validate :must_fit_in_wait_list, :on => :create
  validate :must_fit_in_class,     :on => :update

  scope :waiting,   where(:status => 'waiting')
  scope :confirmed, where(:status => 'confirmed')
  scope :rejected,  where(:status => 'rejected')

  def must_fit_in_wait_list
    unless waiting.count < lecture.available_wait_space
      errors.add(:base, "The waiting list is full")
    end
  end

  def must_fit_in_class
    unless confirmed.count < lecture.available_seats
      errors.add(:status, "The seats are full")
    end
  end
end

顺便说一句，不要忘记在迁移中将 status 的默认值设置为“等待”。

【讨论】：

【解决方案2】：

我认为这在模型中处理得最好。我在之前提出的问题中遇到了类似的问题

Validating :inclusion in rails based on parent Model's attribute value

【讨论】：

【解决方案3】：

感谢 edgerunner 的回答！我找到了另一个简单的解决方案：

validate do |enrollment|
  if(enrollment.lecture.availableSeats <= 0)
    enrollment.errors.add_to_base("This lecture is booked out.") if enrollment.lecture.waitListAvailable <= 0
  end
end

等待列表的警告在控制器中处理：

if @enrollment.save
  if @enrollment.confirmed?
    format.html { redirect_to(@lecture, :notice => 'Enrollment successfull.') }
    format.xml  { render :xml => @lecture, :status => :created, :location => @lecture }
  else
    format.html { redirect_to(@lecture, :alert => 'You're on the waiting list!') }
    format.xml  { render :xml => @lecture, :status => :created, :location => @lecture }
  end

【讨论】：