rails named scopes with lambda. a.k.a. problems with date/time in scopes!

article.rb

Note that scopes defined with scope will be evaluated when they are defined, rather than when they are used. For example, the following would be INCORRECT!!!:
  
  scope :published,
    where(:published => 1)
    .where(:hidden => 0)
    .where("publish_date <= ?", Time.now)

The example above would be "frozen" to the Time.now value when the model class was defined, and so the resultant SQL query would always be the same. The correct way to do this would be via a lambda, which will re-evaluate the scope each time it is called:

  scope :published, -> {
    where(:published => 1)
    .where(:hidden => 0)
    .where("publish_date <= ?", Time.now)
  }