Rails -- Export CSV failing if there is a blank field - ruby-on-rails

Question

I have code in my Rails app that allows me to export a CSV file. It works fine unless there is a record that has a field with no value in it. In that case it fails. As an example, the specific failure I'm getting is saying something liek "No Method Error" and it specifically references "address_line_1" because there are some users with no address_line_1. That is just one example though. Really all fields should be protected against potential blanks. Here is the code:
def download_kids_csv
#csv_headers = ['First',
'Last',
'Child First',
'Child Last',
'Parent Email',
'School',
'Class',
'Address',
'City',
'State',
'Zip',
'Parent Phone']
#kid_data = []
#school = School.find(params[:school_id])
#school.classrooms.each do |classroom|
classroom.kids.includes(:users).each do |kid|
kid.users.each do |parent|
#kid_data << {
first: parent.first_name,
last: parent.last_name,
child_first: kid.first_name,
child_last: kid.last_name,
parent_email: parent.email,
school: #school.name,
class: classroom.classroom_name,
address: parent.addresses.first.address_line_1,
city: parent.addresses.first.city,
state: parent.addresses.first.state,
zip: parent.addresses.first.zip_code,
parent_phone: parent.phones.first.phone_number
}
end
end
end
respond_to do |format|
format.csv do
headers['Content-Disposition'] = "attachment; filename=\"#{#school.name.downcase.gsub(' ', '-')}-data.csv\""
headers['Content-Type'] ||= 'text/csv'
end
end
end

Answer 1

Ok so the problem you are get is because you are calling method on a nil value.
So for example when you do:
kid.first_name
and kid is nil you are doing this
nil.first_name
nil does not implement the first_name method so it throws an error. WHat you could do to circumvent this (its kinda ugly) is this
kid.try(:first_name)
This will prevent you form getting those method missing errors
For those long chains you can do the following
parent.try(:addresses).try(:first).try(:zip_code)
This should save you a lot of headache, but the root cause of your issue is data integrity you would not have to do all of this if you ensured that your data was not blank. I do however understand in the real world it easier said than done. I could give you a lecture about The Law of Demeter and how you should not be running across object to access their attributes, and how thats a code smell of bad organization of data, but its a spread sheet and sometimes you just need the data. Good luck!

Answer 2

To build off of the earlier answer, you can also utilize the so-called lonely operator &. if you're on Ruby 2.3.
An example would look something like this: kid&.first_name.
If you're not on that version of ruby yet, there's a good gem that can help you out in this situation that's a little bit more robust than .try.
Using that gem your code would look like kid.andand.first_name. It might be overkill in this case but the difference here is that it will only perform the first_name method call if kid is not nil. For your longer chains, parent.address.first.zip_code, this would mean that the function chain would exit immediately if parent was nil instead of calling all of the different attributes with try.

Answer 3

Is it possible to use unless or another conditional?
unless parent.addresses.first.address_line_1.blank?
address: parent.addresses.first.address_line_1,
end
or
if parent.addresses.first.address_line_1 != nil
address: parent.addresses.first.address_line_1,
else
address: nil || "address is empty"
end