Question

根据rails指南在before_add块中引发异常有很多会阻止对象添加到集合中。但是，异常提升不是由active_record处理的。

class Order < ActiveRecord::Base
  belongs_to :customer
end

class Customer < ActiveRecord::Base
  has_many :orders, :before_add => :check_credit_limit

  def check_credit_limit(order)
     #If a before_add callback throws an exception, the object does not get added to the collection. 
     raise 'Value cannot be greater than 450' if order.value > 450
  end
end

Failure/Error: customer.orders << order
value cannot be greater than 450

我怎样才能优雅地处理这个问题？

Answer 1

您可以在订单类上添加验证：

class Order < ActiveRecord::Base
  validate :check_value_limit

  def check_value_limit
    errors.add(:value, "can not be greater than 450") if value > 450
  end
end

或者作为上面marc注释的示例，您必须将错误添加到对象并手动处理异常。这是处理创建的基本示例。

更新验证方法以将错误添加到对象：

customer.rb

  def check_credit_limit(order)
     #If a before_add callback throws an exception, the object does not get added to the collection.
     if order.value > 450
       errors.add(:base, "Value can not be greater than 450")
       raise 'Value cannot be greater than 450'
     end 
  end

在控制器中处理创建异常的示例：

def create
  @customer.new(params[:customer])
  if @customer.save
    …
  else
   render :action=>"new"
  end
rescue
  render :action=>"new"
end

您可能希望添加自定义异常类型并专门从中进行救援，以便仍然可以正确抛出任何其他异常。

将项添加到has_many集合时限制

1 个答案: