Rails object returns false on present? but true on !nil?

Question

I have a database object in active record. If I call object.find(1).present? it returns false, but it exists. Calling !object.find(1).nil? returns true.

Why is this? I thought !nil == present?.

Just show us the code, you are playing with. Just do run those code in Rails console and copy and paste those relevant part of your code.. — Arup Rakshit, Jun 06 '14 at 20:03

score 5 · Answer 1 · answered Jun 06 '14 at 20:13

5

nil? and present? are not opposites.

Many things are both not present? and not nil?, such as an empty string or empty array.

"".present? # => false
"".nil? # => false

[].present? # => false
[].nil? # => false

answered Jun 06 '14 at 20:13

user229044

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score 5 · Answer 2 · edited May 23 '17 at 12:00

5

To better answer your question lets look at the implementation:

def present?
  !blank?
end

We don't see nil? mentioned here, just blank?, so lets check out blank? as well:

def blank?
  respond_to?(:empty?) ? !!empty? : !self
end

So essentially, if the object responds_to empty? it will call out to that for the result. Objects which have an empty? method include Array, Hash, String, and Set.

Further Reading

edited May 23 '17 at 12:00

Community

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answered Jun 06 '14 at 21:27

Anthony Michael Cook

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It might be good to point out that in the case of String, `blank?` differs from `empty?` in that a string with all whitespace is blank but not empty. – mckeed Aug 26 '21 at 22:32

Rails object returns false on present? but true on !nil?

2 Answers2