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POWhy polymorphic association doesn't work for STI if type column of the polymorphic association doesn't point to the base model of STI?
 

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  1. POWhy polymorphic association doesn't work for STI if type column of the polymorphic association doesn't point to the base model of STI?
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    <p>I have a case of polymorphic association and STI here.</p> <pre><code># app/models/car.rb class Car &lt; ActiveRecord::Base belongs_to :borrowable, :polymorphic =&gt; true end # app/models/staff.rb class Staff &lt; ActiveRecord::Base has_one :car, :as =&gt; :borrowable, :dependent =&gt; :destroy end # app/models/guard.rb class Guard &lt; Staff end </code></pre> <p>In order for the polymorphic assocation to work, according to the API documentation on Polymorphic Assocation, <a href="http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#label-Polymorphic+Associations" rel="noreferrer">http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#label-Polymorphic+Associations</a> that I have to set <code>borrowable_type</code> to the <code>base_class</code>of STI models, that is in my case is <code>Staff</code>. </p> <p><strong>The question is: Why doesn't it work if the <code>borrowable_type</code> set to STI class?</strong></p> <p>Some test to prove it:</p> <pre><code># now the test speaks only truth # test/fixtures/cars.yml one: name: Enzo borrowable: staff (Staff) two: name: Mustang borrowable: guard (Guard) # test/fixtures/staffs.yml staff: name: Jullia Gillard guard: name: Joni Bravo type: Guard # test/units/car_test.rb require 'test_helper' class CarTest &lt; ActiveSupport::TestCase setup do @staff = staffs(:staff) @guard = staffs(:guard) end test "should be destroyed if an associated staff is destroyed" do assert_difference('Car.count', -1) do @staff.destroy end end test "should be destroyed if an associated guard is destroyed" do assert_difference('Car.count', -1) do @guard.destroy end end end </code></pre> <p>But it seems to be true only with <strong>Staff</strong> instance. The results are:</p> <pre><code># Running tests: F. Finished tests in 0.146657s, 13.6373 tests/s, 13.6373 assertions/s. 1) Failure: test_should_be_destroyed_if_an_associated_guard_is_destroyed(CarTest) [/private/tmp/guineapig/test/unit/car_test.rb:16]: "Car.count" didn't change by -1. &lt;1&gt; expected but was &lt;2&gt;. </code></pre> <p>Thanks</p>
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