Rails Models Validation 1 Word

I try to add a validation from a blog category only limited at 1 word.

But I try this length: { maximum: 1 }

I doesn't work. Is there a validation to validaes only one word and not uniqueness?

Thank you for your answers

You can make a custom validation:

validates :category, uniqueness: true
validate :category_in_1_word

private

def category_in_1_word
  if category.to_s.squish.split.size != 1
    errors.add(:category, 'must be 1 word')
  end
end