Query gotcha

Not so long ago I ran into an issue with a method like this:

class SomeRecord < ActiveRecord::Base
  class << self
    def autocomplete_search(title: nil)
      if title.present?
        where("title ILIKE ?", "%#{title}%")
      else
        self
      end
    end
  end
end

At first glance it looks and works fine:

SomeRecord.where(some_field: "value").autocomplete_search(title: "Hello") # => ✅
SomeRecord.autocomplete_search(title: "Hello").where(some_field: "value") # => ✅

But there is a problem:

SomeRecord.where(some_field: "value").autocomplete_search(title: "")
  # => SELECT * FROM "some_records" ⚠️
SomeRecord.autocomplete_search(title: "").where(some_field: "value")
  # => SELECT * FROM "some_records" WHERE "some_records"."some_field" = ? ✅

Now the first query returns an unexpected result without failing. Why? When title.blank? we return self in SomeRecord.autocomplete_search which is equivalent to SomeRecord.all.

The same happens in the second query but because we chain where(some_field: "value") afterwards we still get the expected result.

By replacing self with all in SomeRecord.autocomplete_search,

class SomeRecord < ActiveRecord::Base
  class << self
    def autocomplete_search(title: nil)
      if title.present?
        where("title ILIKE ?", "%#{title}%")
      else
        all # <-- ✌️
      end
    end
  end
end

we get the expected result.

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In this Gist I have highlighted the issue with an executable test case.