Add predicate method to tell if record exists

[hi-tech-jazz]

Hi @jeremyevans!

Thanks for a great library.

I often find myself using Sequel::Dataset#empty? combined with the ! operator when I want to know if at least one record fulfilling some given conditions exists, however what I would like to write is really the inverse of said predicate to avoid the negation. The obvious name for such a method would be exists? (with the benefit of matching ActiveRecord) but in the case of Sequel, the resemblance to Sequel::Dataset#exists and Sequel::Model#exists? might cause confusion. Before I ponder more on the tricky question of naming I want to ask: Would you be open for considering the addition of such a method or is it an optimization for readability that feels unneeded?

[jeremyevans]

I don't want to add a method for this. The best method name I can think of is not_empty? or non_empty?, neither of which I like. exists? doesn't make sense to me, because a dataset exists regardless of the number of rows in it. For users that want a method for the inverse of empty?, I recommend they add one themselves:

class Sequel::Dataset
  def exists?; !empty? end
end

class Sequel::Model
  def self.exists?; dataset.exists? end
end

[JonathanFrias]

What about any?

[jeremyevans]

any? is already defined via Enumerable and does work, though it is certainly suboptimal for large tables. I suppose we could optimize the case where no arguments or block are provided to act as !empty?.

[eriklovmo]

I noticed that the any_not_empty extension is already available, maybe that is good enough.

[jeremyevans]

Agreed, no need to include this in core if an extension is already available. That extension should be updated, because since Ruby 2.5, any? can take a pattern argument. I'll work on that shortly.

[jeremyevans]

Fixed in e728617