Enumerable#all?
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returns true for an empty collection. This totally makes sense but you have to think about it when making assumptions on relations which might be empty.
[].all?(&:will_never_be_called_here) => true
Example with empty collection
class Researcher < ActiveRecord::Base
has_many :papers
end
class Paper
validates :topic, inclusion: { in: ['computer_science', 'mathematics', 'economy'] }
end
Easy goal: Delete all researches who write only about computer science.
# Bad (deletes researchers with no topic at all)
Researcher.find_each |researcher| do
if researcher.papers.all? { |topic| topic == 'computer_science' }
researcher.destroy!
end
end
# Good
Researcher.find_each |researcher| do
if researcher.papers.present? && researcher.papers.all? { |topic| topic == 'computer_science' }
researcher.destroy!
end
end
There are more methods in Enumerable (returning boolean values) where you might need to think twice with empty collections.
Posted by Emanuel to makandra dev (2018-01-11 08:41)