rails：nil：NilClass的未定义方法“>”

Question

I'm a beginner in rails and I need to compare 2 DateTime on my controller :

@b = Book.find(params[:book][:id])
if @b.expiry_date > DateTime.now
  ... something here ...
end

But I get this error :

undefined method `>' for nil:NilClass

Anyone have an idea why ?

Answer 1

Operators are methods in ruby, so your undefined method '>' for nil:NilClass error indicates that @b.expiry_date is nil on this line: if @b.expiry_date > DateTime.now .

You can use a short-circuiting logic to only evaluate the condition if @b.expiry_date is present.

if @b.expiry_date && (@b.expiry_date > DateTime.now)

The if expressions is only true if both sides of the && are also true, so (@b.expiry_date > DateTime.now) won't be executed if the first condition, @b.expiry_date , is false or nil.

Otherwise, you'll need to add logic/validations to ensure the existence of expiry_date .

Answer 2

Just add a check that the record isn't nil in your if statement as shown:

    @b = Book.find(params[:book][:id])
      if !@b.expiry_date.nil? && @b.expiry_date > DateTime.now
      ... something here ...
    end

If all Books are supposed to have expiry dates you should add a validation that insists an expiry date is included when creating/updating a Book record in your Book Model!