ruby / rails interview questions

i’ve been digging around lately for interview questions to use when interviewing a ruby and rails candidate.

there are few good resources for this:

ritirisi

joe sniff

i’m adding a few more with some solutions, designed to test the breadth of someone’s knowledge.
h3. what do you not like about ruby on rails? identify its weak points.

the answers i expect here are fixtures, routes, scalability. bonus points for identifying the weakness in using multiple databases.

a good followup on scalability is: how have you in the past dealt with the scalability problems, and what does your preferred deployment environment look like?

what is the difference between a symbol and a string? when should they be used?

a symbol has a shorter reference number, which makes it faster to look up. if you’re using something as a reference string, a symbol is a good idea. if you’re planning on a string being editable, then a string is a better idea.

good information on this here: 13 ways of looking at a ruby symbol

when would you use request.xhr?

to test for an XmlHttpRequest, if you were writing a single method to deal with each request type. bonus: this has been dusted somewhat in rails 2, wherein you deal with the response where it belongs, in the response:

1  def action
2    # .. some code
3    respond_to do |format| do
4      format.html { ... }
5      format.js  { ... }
6      format.xml  { ... }
7    end 
8  end

when would you use has_many :through?

to create an association without creating a new table, if the information can be related through an existing table.

when would you use a polymorphic association? is there a better method?

the better method is has_many_polymorphs . generally, you want to use a polymorphic association when you want to treat a group of objects uniformly from a parent’s point of view.

when is it appropriate to use a helper method? where should that helper method live?

helper methods should generate markup. that is all. the helper method should live in the controller of a particular object if that markup is particular that object, especially if it is similar or has the same method signature across a number of objects, and each is handled differently (but share partials). generally applicable helpers should live in the helpers … [read more >>]