this in conjunction with using a scope that joins
an association allows fetching attributes of associated
records.

class Organization
  belongs_to :contact

  scope :with_contact, -> { joins(:contact) }
end

autocomplete :organization, :name, extra_data: ['contacts.email'],
select_method: :pluck, scopes: [:with_contact]

f.autocomplete_field :name,
autocomplete_organization_name_product_path, update_elements: {id:
'#products_organization_attributes_id', 'contacts.email':
'#products_contact_attributes_email'}

because rails internally does a uniq before querying