Enumerable predicates on query attributes

[jgaskins]

In jgaskins/perpetuity#32, it was proposed that we add predicate methods to query attributes to match the ones in Ruby's Enumerable module for queries like this:

Perpetuity[User].select { |user| user.friends.any? }

Using Postgres' json_array_length function, this is totally doable:

• count — SQL: json_array_length(#{attribute})
• any? — attribute.count > 0
• none? — !attribute.any?
• one? — attribute.count == 1

[jgaskins]

Fixed in 17867453cbbd8e27c932bb4ac35e38af9cca37fa