How to handle NilClass elegantly - ruby-on-rails

Question

I am trying to avoid NoMethod errors due to NilClass. My code looks like this:
#branded, #nonbranded, #unknown, #affiliate, #social, #referral, #paid, #direct, #email = [], [], [], [], [], [], [], [], []
count = 0
while count < 6
date = SDLW + count
#TODO There has to be a better way than this.
branded_check = Metric.first(start_date: date, end_date: date, source: 'branded')
nonbranded_check = Metric.first(start_date: date, end_date: date, source: 'nonbranded')
unknown_check = Metric.first(start_date: date, end_date: date, source: 'unknown')
affiliate_check = Metric.first(start_date: date, end_date: date, source: 'affiliate')
social_check = Metric.first(start_date: date, end_date: date, source: 'social')
referral_check = Metric.first(start_date: date, end_date: date, source: 'referral')
paid_check = Metric.first(start_date: date, end_date: date, source: 'paid')
direct_check = Metric.first(start_date: date, end_date: date, source: 'direct')
email_check = Metric.first(start_date: date, end_date: date, source: 'email')
branded_check = branded_check.nil? ? 0 : branded_check.visits
nonbranded_check = nonbranded_check.nil? ? 0 : nonbranded_check.visits
unknown_check = unknown_check.nil? ? 0 : unknown_check.visits
affiliate_check = affiliate_check.nil? ? 0 : affiliate_check.visits
social_check = social_check.nil? ? 0 : social_check.visits
referral_check = referral_check.nil? ? 0 : referral_check.visits
paid_check = paid_check.nil? ? 0 : paid_check.visits
direct_check = direct_check.nil? ? 0 : direct_check.visits
email_check = email_check.nil? ? 0 : email_check.visits
#branded << branded_check
#nonbranded << nonbranded_check
#unknown << unknown_check
#affiliate << affiliate_check
#social << social_check
#referral << referral_check
#paid << paid_check
#direct << direct_check
#email << email_check
count += 1
end
I am sure there has to be a cleaner, more concise way to do this. Despite googling and reading around I haven't been able to figure it out. Any ideas on how to refactor would be much appreciated.

Answer 1

Definitely, create a method to avoid to repeat yourself
def visits(tag, date)
check = Metric.first(start_date: date, end_date: date, source: tag)
check.present? ? check.visits : 0 # or 'check.nil? ? 0 : check.visits' if you prefer
end
And in your method
count = 0
while count < 6
date = SDLW + count
#branded << visits('branded', date)
#nonbranded << visits('nonbranded', date)
...
count += 1
end

Answer 2

Let's put calls to Metric.first in a block and set instance variables using instance_variable_set.
['branded', 'nonbranded', ...].each do |source|
visits = 0.upto(5).map do |count|
date = SDLW + count
metric = Metric.first(start_date: date, end_date: date, source: source)
if metric.nil? then 0 else metric.visits end
end
instance_variable_set "##{source}".to_sym, visits
end

Answer 3

In addition to the other solutions, the while-loop can probably be replaced by:
(SDLW...SDLW+6).each do |date|
# date = SDLW + count #This line is superfluous
#branded << visits('branded', date)
#or one of the other solutions
#etc
# count += 1 # remove this line
end

Answer 4

I've made only for one source just for example.
#branded, #nonbranded, #unknown, #affiliate, #social, #referral, #paid, #direct, #email = [], [], [], [], [], [], [], [], []
class Metric < ActiveRecord::Base
scope :dates, lambda { |start_date, end_date| where(:start_date => start_date, :end_date => end_date) }
scope :branded, lambda { where(:source => "branded") }
# ... other scopes
end
# ...
6.times do |count|
date = SDLW + count
by_date = Metric.dates(date, date)
#branded << by_date.branded.try(:visits).to_i
# ... other sources
end
update:
Refactored solution using instance_variable_set idea from Jan solution and Dave Newton request.
6.times do |count|
date = SDLW + count
[:branded, :nonbranded, :unknown, :affiliate, :social, :referral, :paid, :direct, :email].each do |source|
instance_variable_set :"##{source}", [] unless instance_variable_get :"##{source}"
visits = Metric.first(start_date: date, end_date: date, source: source).try(:visits).to_i
instance_variable_set :"##{source}", instance_variable_get(:"##{source}").push(visits)
end
end