---
title: when things happen
teaser:
tags: web,rails
author: Jared Carroll
published_on: 2007-07-20
---

Recently in a Rails app, I ran into a strange bug.

In this app, we had users and articles.  A `User` could write any number of
`Article` s.

```ruby
class User < ActiveRecord::Base

  has_many :articles

end

class Article < ActiveRecord::Base

  belongs_to :user

end
```

On a `User`'s personal page we show their recent articles.  At first I
implemented it using another `#has_many` like:

```ruby
class User < ActiveRecord::Base

  has_many :articles

  has_many :recent_articles,
    :class_name => 'Article',
    :conditions => ['created_on > ?', 2.weeks.ago]

end

class Article < ActiveRecord::Base

  belongs_to :user

end
```

Now this worked for a day.

This is why.

Say this app went online at 7/15/2007.  When that `User` class was loaded its
`#has_many` calls got executed once, which means the value of `2.weeks.ago` was
7/1/2007.  So `User#recent_articles` would return `articles` created after
7/1/2007.

On 7/16/2007 `User#recent_articles` would still return `articles` created after
7/1/2007.  Which is wrong because 2 weeks ago is 7/2/2007 not 7/1/2007.

In other words, `ActiveRecord` is only going to execute that
`User#recent_articles` `#has_many` declaration once.  The solution is to create
an instance method instead.

```ruby
class User < ActiveRecord::Base

  def recent_articles
    articles.find :all,
      :conditions => ['created_on > ?', 2.weeks.ago]
  end

end
```