Rails query with array quoted using the asterisk parameter

The easiest thing to do would be to reverse the argument order and let the splat (*) swallow up everything that isn't the account:

def has_account_role?(account, *role_names)

Then you'd say things like this:

user.has_account_role?(account, ['member', 'supervisor'])
user.has_account_role?(account, 'member', 'supervisor')

You'd also want to use the hash form of where inside the method:

self.account_user_roles
    .joins(:role)
    .where(roles: { name: role_names }, account_id: account.id)
    .present?

so that where can use the appropriate SQL (roles.name = ... or roles.name in (...)) depending on what role_names ends up looking like.

BTW, a splat in a method signature:

def has_role?(*role_names)
  #... 
end

simply collects all the splatable arguments to the method into a single array (called role_names in this case) but it doesn't flatten the array. That means that these two calls:

user.has_role?(['super admin', 'member'])
user.has_role?('super admin', 'member')

are different things. In the first one, role_names looks like [['super admin', 'member']] (i.e. an array inside an array) and in the second one, role_names is just ['super admin', 'member'] (i.e. just a simple array). The where(:name => role_names) inside the method will flatten the array behind your back but they're still quite different as far as has_role? and the caller are concerned and not every method that has_role? calls will flatten arrays the way where does.

With that in mind, you might want to manually flatten your splats:

def has_role?(*role_names)
  role_names = role_names.flatten
  # Do whatever needs to be done now that you know that
  # `role_names` is a flat array.
  # ...
end