This post originated from an RSS feed registered with PHP Buzz by Joe Grossberg. Original Post: Query Methods in Rails and true/false Feed Title: Joe Grossberg Feed URL: http://feeds.feedburner.com/joegrossbergatom/ Feed Description: My bullshit, your brain. Latest PHP Buzz Posts Latest PHP Buzz Posts by Joe Grossberg Latest Posts From Joe Grossberg

In Ruby, unlike many other languages, only false and nil evaluate to false.

However, I learned today that the ActiveRecord::Base class in Rails gives us not only attribute setters and getters, but a query method too.

And this query method has its own rules.

Where o is an instance of an ActiveRecord class, and name is a column/attribute:

>> o.name = nil
=> nil
>> o.name?
=> false

>> o.name = false
=> false
>> o.name?
=> false

>> o.name = ''
=> ""
>> o.name?
=> false

>> o.name = 0
=> 0
>> o.name?
=> false

>> o.name = []
=> []
>> o.name?
=> true

>> o.name = {}
=> {}
>> o.name?
=> true

>> o.name = 0.0
=> 0.0
>> o.name?
=> true

So this has its own set of rules: false and nil still evaluate to false, but so do 0 and an empty string. However, empty arrays, empty hashes and the 0.0 float evaluate to true.

For [] and {}, you can do foo.empty?. But for 0.0, you have to do foo.zero?.

Ugh; more arbitrary stuff to memorize (or test in the console).

I wish there was some method that combined ?, empty? and zero?. Perhaps there is one that I've overlooked?