How to have a maintainable username blacklist

Question

My app is a social platform and I want to have the support-team being able to maintain a blacklist for nicknames. Therefore I have a model Blacklist that contains the different names.

Now I tried with the validates_exclusion_of to map these into the in: but it raises the following error,

wrong number of arguments (given 1, expected 0)

validates_exclusion_of :nickname, in: -> { 
  where(Blacklist.select(:name).map(&:name).uniq.to_s)
}, message: "This nickname is not allowed"

Answer 1

You don't need to wrap the values to exclude within a lambda, it'll work as is if you pass just the Blacklist AR query result.

validates_exclusion_of :nickname,
                       in: Blacklist.select(:name).map(&:name).uniq.to_s,
                       message: 'This nickname is not allowed'

Notice, you can use the ActiveRecord::Calculations#pluck in order to get just the names from Blacklist, getting rid of the select and map combination, and use ActiveRecord::QueryMethod#distinct to get non-repeated values.

With that you don't need the uniq and to_s step. The last one, because the validation is waiting for an enumerable object, and you'd be passing a string.

Something like:

validates_exclusion_of :nickname,
                       in: Blacklist.distinct.pluck(:name),
                       message: 'This nickname is not allowed'

The where you're using on the validation won't work, as it's applying a WHERE statement without passing a column name to check, so you'll get an ActiveRecord::StatementInvalid .