Ruby - NoMethodError（nil:NilClass 的未定义方法）：
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Ruby - NoMethodError (undefined method for nil:NilClass):
提问by Dodinas
I'm having some difficulty trying to figure out what I am doing wrong. My ActiveRecordquery is returning nilwhich I think is causing NoMethodErrorto be raised.
我在试图弄清楚我做错了什么时遇到了一些困难。我的ActiveRecord查询正在返回nil，我认为这会导致NoMethodError提出。
Here's what I have:
这是我所拥有的：
@number_exclude_list = ["1234567890", "2223334545"]
@available_number = UserNumber.where.not(:user_num => @number_exclude_list)
Which returns an empty set of rows:
它返回一组空的行：
=> #<ActiveRecord::Relation []>
So, then I have:
那么，我有：
if (@available_number.empty?)
inform_user_empty
else
do_my_other_function
But, I get:
但是，我得到：
`NoMethodError (undefined method 'inform_user_empty' for nil:NilClass)`
I have tried: @available_number.blank?and `@available_number.nil?
我试过：@available_number.blank?和`@available_number.nil?
And I still get the same NoMethodError. Any ideas on what I am doing wrong here?
而且我仍然得到相同的结果NoMethodError。关于我在这里做错了什么的任何想法？
回答by Малъ Скрылевъ
The exception text NoMethodError (undefined method 'inform_user_empty' for nil:NilClass)says that is was a call to instance method #inform_user_emptyof the nilclass'es instance, and since nilhas no instance method rubyinterpreter throwed that exception. I see the two main reason for it:
异常文本NoMethodError (undefined method 'inform_user_empty' for nil:NilClass)说这是对类实例的实例方法#inform_user_empty的调用nil，并且由于nil没有实例方法ruby解释器抛出了该异常。我认为有两个主要原因：
selfkeyword variable hasnilvalue, I believe not in the reason, because you do a call from a controller, as you've saidApplicationController. To make sure thatselfisn'tnil, change the code to the following one:if @available_number.empty? p self self.inform_user_emptyrerun the action, and look at the result.
The exception has been thrown from another place. So you have to specify the full trace log in your post.
self关键字变量具有nil价值，我不相信原因，因为正如您所说，您从控制器进行调用ApplicationController。要确保self不是nil，请将代码更改为以下代码：if @available_number.empty? p self self.inform_user_empty重新运行该操作，然后查看结果。
异常已从另一个地方抛出。所以你必须在你的帖子中指定完整的跟踪日志。
回答by Rajesh Omanakuttan
Please run the below line in your console:
请在您的控制台中运行以下行：
@available_number = UserNumber.where.not(:user_num => @number_exclude_list)
it returns an ArgumentError: wrong number of arguments (0 for 1+)since it is not the way to check NOT INcondition in Rails activerecord.
它返回一个，ArgumentError: wrong number of arguments (0 for 1+)因为它不是NOT IN在 Rails activerecord 中检查条件的方法。
Replace it with:
替换为：
User.where('user_num NOT IN (?)',@number_exclude_list)
and then do:
然后做：
if @available_number == nil
inform_user_empty
else
do_my_other_function
end
Hoep that will resolve the issue. Please let me know if it really helped you.
希望能解决问题。请让我知道它是否真的对你有帮助。
