Getting undefined method `to_sym' from FactoryGirl create - ruby-on-rails

Question

I have a simple spec:
describe Setting do
subject { create(:setting) }
it { should be_valid }
end
with the factory:
FactoryGirl.define do
factory :setting do
key "some_key"
value "The appropriate value"
end
end
When I run the spec:
rake spec SPEC=spec/models/setting_spec.rb
I get the following error:
1) Setting should be valid
Failure/Error: it { should be_valid }
NoMethodError:
undefined method `to_sym' for nil:NilClass
# ./spec/models/setting_spec.rb:6:in `block (2 levels) in <top (required)>'
I tried using a let(:setting) in place of the subject line and got the same error.
EDIT Per comments:
The error refers to the line it { should be_valid }
The model is:
class Setting < ActiveRecord::Base
attr_accessor :key, :value
validates_uniqueness_of :key
end
Here's the trace:
# /var/lib/gems/1.9.1/gems/activerecord-3.2.16/lib/active_record/validations/uniqueness.rb:26:in `validate_each'
# /var/lib/gems/1.9.1/gems/activemodel-3.2.16/lib/active_model/validator.rb:153:in `block in validate'
# /var/lib/gems/1.9.1/gems/activemodel-3.2.16/lib/active_model/validator.rb:150:in `each'
# /var/lib/gems/1.9.1/gems/activemodel-3.2.16/lib/active_model/validator.rb:150:in `validate'
# /var/lib/gems/1.9.1/gems/activesupport-3.2.16/lib/active_support/callbacks.rb:310:in `_callback_before_1986'
# /var/lib/gems/1.9.1/gems/activesupport-3.2.16/lib/active_support/callbacks.rb:407:in `_run__3464288744618424855__validate__1974049388273351148__callbacks'
# /var/lib/gems/1.9.1/gems/activesupport-3.2.16/lib/active_support/callbacks.rb:405:in `__run_callback'
# /var/lib/gems/1.9.1/gems/activesupport-3.2.16/lib/active_support/callbacks.rb:385:in `_run_validate_callbacks'
# /var/lib/gems/1.9.1/gems/activesupport-3.2.16/lib/active_support/callbacks.rb:81:in `run_callbacks'
# /var/lib/gems/1.9.1/gems/activemodel-3.2.16/lib/active_model/validations.rb:228:in `run_validations!'
# /var/lib/gems/1.9.1/gems/activemodel-3.2.16/lib/active_model/validations/callbacks.rb:53:in `block in run_validations!'
# /var/lib/gems/1.9.1/gems/activesupport-3.2.16/lib/active_support/callbacks.rb:403:in `_run__3464288744618424855__validation__1974049388273351148__callbacks'
# /var/lib/gems/1.9.1/gems/activesupport-3.2.16/lib/active_support/callbacks.rb:405:in `__run_callback'
# /var/lib/gems/1.9.1/gems/activesupport-3.2.16/lib/active_support/callbacks.rb:385:in `_run_validation_callbacks'
# /var/lib/gems/1.9.1/gems/activesupport-3.2.16/lib/active_support/callbacks.rb:81:in `run_callbacks'
# /var/lib/gems/1.9.1/gems/activemodel-3.2.16/lib/active_model/validations/callbacks.rb:53:in `run_validations!'
# /var/lib/gems/1.9.1/gems/activemodel-3.2.16/lib/active_model/validations.rb:195:in `valid?'
# /var/lib/gems/1.9.1/gems/activerecord-3.2.16/lib/active_record/validations.rb:69:in `valid?'
# /var/lib/gems/1.9.1/gems/rspec-expectations-2.14.5/lib/rspec/expectations/handler.rb:24:in `handle_matcher'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/memoized_helpers.rb:68:in `should'
# ./spec/models/setting_spec.rb:6:in `block (2 levels) in <top (required)>'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/example.rb:114:in `instance_eval'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/example.rb:114:in `block in run'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/example.rb:254:in `with_around_each_hooks'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/example.rb:111:in `run'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/example_group.rb:390:in `block in run_examples'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/example_group.rb:386:in `map'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/example_group.rb:386:in `run_examples'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/example_group.rb:371:in `run'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/command_line.rb:28:in `block (2 levels) in run'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/command_line.rb:28:in `map'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/command_line.rb:28:in `block in run'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/reporter.rb:58:in `report'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/command_line.rb:25:in `run'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/runner.rb:77:in `rescue in run'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/runner.rb:73:in `run'
# /var/lib/gems/1.9.1/gems/rspec-core-2.14.7/lib/rspec/core/runner.rb:17:in `block in autorun'
spec_helper.rb: http://pastebin.com/6fzDXnux

Answer 1

The direct cause for this error is that the class derives from ActiveRecord::Base, and ActiveRecord can't determine the primary key (required by AR for validating uniqueness). Most likely, this is happening either because you haven't run migrations to create the settings table, or you created the settings table without a primary key.
The offending line (based on the backtrace provided):
relation = relation.and(table[finder_class.primary_key.to_sym].not_eq(record.send(:id))) if record.persisted?
Note that to_sym is being called on finder_class.primary_key.

Answer 2

you can also solve same by adding below line in your model.
self.primary_key = 'id'
e.g.
Class Person
self.primary_key = 'id'
end