Ruby Undefined method downcase

Question

I'm getting an exception in the following piece of code. Can someone please tell me what I'm doing wrong, and how I can prevent it?

def self.find_by_data(data = {})
            where(name_canonical: data['name'].downcase.gsub(/\s+/, ''),
                  fuel:           data['fuel'],
                  trim_canonical: data['trim'].downcase.gsub(/\s+/, ''),
                  year:           data['year']).first
        end

Exception:

/Users/charlie/Documents/WIP/projectx/ar_models.rb:35:in `find_by_data': undefined method `downcase' for nil:NilClass (NoMethodError)ooooooooooooooooooooooooo| ETA:   0:00:00
    from /Users/charlie/.rvm/gems/ruby-2.0.0-p0/gems/activerecord-4.0.0/lib/active_record/relation/delegation.rb:36:in `block in find_by_data'
    from /Users/charlie/.rvm/gems/ruby-2.0.0-p0/gems/activerecord-4.0.0/lib/active_record/associations/collection_proxy.rb:845:in `block in scoping'
    from /Users/charlie/.rvm/gems/ruby-2.0.0-p0/gems/activerecord-4.0.0/lib/active_record/relation.rb:270:in `scoping'
    from /Users/charlie/.rvm/gems/ruby-2.0.0-p0/gems/activerecord-4.0.0/lib/active_record/associations/collection_proxy.rb:845:in `scoping'
    from /Users/charlie/.rvm/gems/ruby-2.0.0-p0/gems/activerecord-4.0.0/lib/active_record/relation/delegation.rb:36:in `find_by_data'
    from /Users/charlie/Documents/WIP/projectx/ar_models.rb:132:in `create_or_assign_existing'
    from /Users/charlie/Documents/WIP/projectx/app.rb:230:in `block (2 levels) in work'
    from /Users/charlie/.rvm/gems/ruby-2.0.0-p0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in `with_connection'
    from /Users/charlie/Documents/WIP/projectx/app.rb:80:in `block in work'
    from /Users/charlie/.rvm/gems/ruby-2.0.0-p0/gems/parallel-0.6.3/lib/parallel.rb:319:in `call'
    from /Users/charlie/.rvm/gems/ruby-2.0.0-p0/gems/parallel-0.6.3/lib/parallel.rb:319:in `call_with_index'
    from /Users/charlie/.rvm/gems/ruby-2.0.0-p0/gems/parallel-0.6.3/lib/parallel.rb:179:in `block (3 levels) in work_in_threads'
    from /Users/charlie/.rvm/gems/ruby-2.0.0-p0/gems/parallel-0.6.3/lib/parallel.rb:326:in `with_instrumentation'
    from /Users/charlie/.rvm/gems/ruby-2.0.0-p0/gems/parallel-0.6.3/lib/parallel.rb:177:in `block (2 levels) in work_in_threads'
    from /Users/charlie/.rvm/gems/ruby-2.0.0-p0/gems/parallel-0.6.3/lib/parallel.rb:171:in `loop'
    from /Users/charlie/.rvm/gems/ruby-2.0.0-p0/gems/parallel-0.6.3/lib/parallel.rb:171:in `block in work_in_threads'
    from /Users/charlie/.rvm/gems/ruby-2.0.0-p0/gems/parallel-0.6.3/lib/parallel.rb:62:in `block (2 levels) in in_threads'

Answer 1

When you see "undefined method ... for nil:NilClass" it means you have a nil value you're trying to call the method on.

In this case, something like data['name'] is not defined.

To make this more bullet-proof:

data['name'].to_s.downcase.gsub(/\s+/, '')

This converts everything to string to start with. nil.to_s is an empty string by default, so it's safe.