find_named_scope.rb

class ActiveRecord::Base
  named_scope :conditions, lambda { |*args| {:conditions => args} }
end

  def self.find_by(email, nick, firstname, lastname)
    scope = self.scoped({})
    scope = scope.conditions "members.email LIKE ?", "%#{email}%" unless email.blank?
    scope = scope.conditions "members.nick LIKE ?", "%#{nick}%" unless nick.blank?
    scope = scope.conditions "members.firstname LIKE ?", "%#{firstname}%" unless firstname.blank?
    scope = scope.conditions "members.lastname LIKE ?", "%#{lastname}%" unless lastname.blank?
    scope
  end