Shoulda-matchers: Has many through association: undefined method `klass' for nil:NilClass

Created on 6 Nov 2014 · 15Comments · Source: thoughtbot/shoulda-matchers

Hi!

I have an Subject model which should have many Photos through SubjectPhotoAssignments. When I test this, I get undefined method 'klass' for nil:NilClass. Here is my setup:

class Subject < ActiveRecord::Base
  belongs_to :project, touch: true
  has_many :photos, through: :subject_photo_assignments
end

class SubjectPhotoAssignment < ActiveRecord::Base
  belongs_to :photo
  belongs_to :subject, touch: true
end

class Photo < ActiveRecord::Base
  belongs_to :project, touch: true
  has_many :album_photo_assignments
  has_many :subject_photo_assignments
end

Here is the failing test:

RSpec.describe Subject, type: :model do
  it { should have_many(:photos).through(:subject_photo_assignments) }
end

  2) Subject should have many photos through subject_photo_assignments
     Failure/Error: it { should have_many(:photos).through(:subject_photo_assignments) }
     NoMethodError:
       undefined method `klass' for nil:NilClass

What am I doing wrong? Any help is greatly appreciated. Let me know if more context would be helpful.

I'm using v2.7.0

Source

xtagon

👍1

Most helpful comment

You're saying that Subject.has_many :photos, through: :subject_photo_assignments, but you don't have a :subject_photo_assignments association.

Ideally, we should probably have a check to ensure that your through association exists. But that's why you're getting an error.

mcmire on 6 Nov 2014

👍9

All 15 comments

Yeah, can you re-run the tests with the --backtrace option?

mcmire on 6 Nov 2014

  Failure/Error: it { should have_many(:photos).through(:subject_photo_assignments) }
     NoMethodError:
       undefined method `klass' for nil:NilClass
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activerecord-4.1.7/lib/active_record/reflection.rb:537:in `source_reflection'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activerecord-4.1.7/lib/active_record/reflection.rb:725:in `derive_class_name'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activerecord-4.1.7/lib/active_record/reflection.rb:176:in `class_name'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/shoulda-matchers-2.7.0/lib/shoulda/matchers/active_record/association_matcher.rb:968:in `rescue in class_exists?'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/shoulda-matchers-2.7.0/lib/shoulda/matchers/active_record/association_matcher.rb:965:in `class_exists?'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/shoulda-matchers-2.7.0/lib/shoulda/matchers/active_record/association_matcher.rb:847:in `matches?'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-expectations-3.1.2/lib/rspec/expectations/handler.rb:48:in `handle_matcher'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/memoized_helpers.rb:81:in `should'
     # ./spec/models/subject_spec.rb:5:in `block (2 levels) in <top (required)>'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example.rb:152:in `instance_exec'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example.rb:152:in `block in run'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example.rb:222:in `call'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example.rb:222:in `call'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-rails-3.1.0/lib/rspec/rails/adapters.rb:72:in `block (2 levels) in <module:MinitestLifecycleAdapter>'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example.rb:322:in `instance_exec'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example.rb:322:in `instance_exec'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/hooks.rb:380:in `execute_with'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/hooks.rb:446:in `block (2 levels) in run'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example.rb:222:in `call'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example.rb:222:in `call'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/hooks.rb:447:in `run'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/hooks.rb:500:in `run'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example.rb:331:in `with_around_example_hooks'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example.rb:149:in `run'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example_group.rb:490:in `block in run_examples'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example_group.rb:486:in `map'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example_group.rb:486:in `run_examples'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example_group.rb:453:in `run'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:111:in `block (2 levels) in run_specs'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:111:in `map'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:111:in `block in run_specs'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/reporter.rb:53:in `report'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:107:in `run_specs'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:85:in `run'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:69:in `run'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:37:in `invoke'
     # /home/xtagon/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/exe/rspec:4:in `<top (required)>'
     # /home/xtagon/.rbenv/versions/2.1.4/bin/rspec:23:in `load'
     # /home/xtagon/.rbenv/versions/2.1.4/bin/rspec:23:in `<main>'

xtagon on 6 Nov 2014

You're saying that Subject.has_many :photos, through: :subject_photo_assignments, but you don't have a :subject_photo_assignments association.

Ideally, we should probably have a check to ensure that your through association exists. But that's why you're getting an error.

mcmire on 6 Nov 2014

👍9

I added the :subject_photo_assignments association and the tests pass. For some reason I was thinking that argument was specifying the join table, not another association. Thank you very much for clearing up my blunder!

Feel free to close the issue, unless you want to keep it open for adding a different error message.

xtagon on 6 Nov 2014

👍7

Sounds good, glad I could help.

mcmire on 6 Nov 2014

I have this error with code like this one:

class Subject < ActiveRecord::Base
  has_one :subject_photo_assignment
  has_many :photos, through: :subject_photo_assignments
end

1v on 18 Mar 2017

@1v You have a subject_photo_assignment association, but you don't have a subject_photo_assignments association (note the "s" at the end).

mcmire on 21 Mar 2017

@mcmire it's working with "s" too, but tests failing.

1v on 21 Mar 2017

@1v Okay. Have you tried:

class Subject < ActiveRecord::Base
  has_one :subject_photo_assignment
  has_many :photos, through: :subject_photo_assignment   # note that this is singular, not plural
end

mcmire on 22 Mar 2017

@mcmire yeah that's how I do right now. But Rails accepts plural too. It took me time to figure out because error message not informative.

1v on 22 Mar 2017

@1v Okay, fair enough. I'll re-open this issue.

mcmire on 23 Mar 2017

I also have this error with this "setup":

ruby module Hanuman class Observation < ActiveRecord::Base belongs_to :survey, touch: true end end

ruby Hanuman::Observation.class_eval do has_one :user, through: :survey end

ruby module Hanuman RSpec.describe ObservationAnswer, type: :model do it { is_expected.to have_one(:user).through(:survey) } end end

Failure/Error: it { is_expected.to have_one(:user).through(:survey) }
NoMethodError:
  undefined method `klass' for nil:NilClass

esbanarango on 18 May 2017

Related issue: #646. #723 may solve both of these at once, I'll have to check.

mcmire on 9 Jun 2019

I can verify that the reported issue has been fixed in the version 4.4.1, so we can close this issue for now.

Before:

     Failure/Error: it { should have_many(:words).through(:pag) }

     NoMethodError:
       undefined method `class_name' for nil:NilClass
       Did you mean?  class_eval

After:

     Failure/Error: it { should have_many(:words).through(:pag) }
       Expected Book to have a has_many association called words through pages (Could not find the source association(s) "word" or :words in model Page. Try 'has_many :words, :through => :pages, :source => <name>'. Is it one of book?)

_Error text differs as i'm using rails 6.1.0.alpha_