class ActiveRecord::Validations::UniquenessValidator

def validate_each(record, attribute, value)
  finder_class = find_finder_class_for(record)
  value = map_enum_attribute(finder_class, attribute, value)
  return if record.persisted? && !validation_needed?(finder_class, record, attribute)
  relation = build_relation(finder_class, attribute, value)
  if record.persisted?
    if finder_class.primary_key
      relation = relation.where.not(finder_class.primary_key => [record.id_in_database])
    else
      raise UnknownPrimaryKey.new(finder_class, "Cannot validate uniqueness for persisted record without primary key.")
    end
  end
  relation = scope_relation(record, relation)
  if options[:conditions]
    conditions = options[:conditions]
    relation = if conditions.arity.zero?
      relation.instance_exec(&conditions)
    else
      relation.instance_exec(record, &conditions)
    end
  end
  if relation.exists?
    error_options = options.except(:case_sensitive, :scope, :conditions)
    error_options[:value] = value
    record.errors.add(attribute, :taken, **error_options)
  end
end