combine scopes from a hash

with_scopes.rb

# Allow query usings scopes and arguments from a hash.  Useful for
# making index actions.
#
# Example:
#
#   User.with_scopes(:search => "Fred")
#
# Where +search+ is a named scope on +User+ which excepts a parameter.
module WithScopes
  # Determine if named scope exists.
  def has_scope?(name)
    scopes.keys.map(&:to_s).include?(name.to_s)
  end
  
  # Run through given scopes.
  def with_scopes(params)
    params.select do |k,_|
      has_scope?(k)
    end.inject(self) do |scope,(k,v)|
      scopes[k.to_sym][scope, *v]
    end
  end
end

class ActiveRecord::Base; extend WithScopes; end