Ruby on Rails® for Microsoft Developers

5.12. Using named_scope

At this stage your The Rails Noob blog publishes every single article in the database regardless of its published or unpublished status. This is because in the index action you used a finder method, which retrieves all the records from the articles table:

@articles = Article.find(:all, :order => "published_at DESC")

You can change this in order to select only published articles by specifying a condition in the query:

@articles = Article.find(:all, :conditions => { :published => true }, :order =>
"published_at DESC")

This is converted into the SQL query:

SELECT * FROM "articles" WHERE ("articles"."published" = 't') ORDER BY published_at
DESC

You don't want to show all the published articles though. For example, if an article is set as published, but its publication date is in the future, that article is scheduled and should be shown only when its publication date is presently due or if it was in the past. You need to indicate two conditions to the find method, then, as shown here:

@articles = Article.find(:all, :conditions => ["published = ? AND published_at <=
?", true, Time.now], :order => "published_at DESC")

Notice how you specify the conditions by assigning an array to the :conditions key. This array contains the SQL condition, and the two parameters that the condition requires, in the order that they appear within it. The resulting SQL query will resemble the following:

SELECT * FROM "articles" WHERE (published = 't' AND published_at <= '2008-07-16 ...