Add task to add option_id to existing answers

Note: to avoid confusion, "answer" will mean a row in the poll_answers
table and "choice" will mean whatever is in the "answer" column of that
table (I'm applying the same convention in the code of the task).

In order make this task perform reasonably on installations with
millions of votes, we're using `update_all` to update all the answers
with the same choice at once. In order to do that, we first need to
check the existing choices and what are the possible option_ids for
those choices.

Note that, in order for this task to work, we need to remote the
duplicate answers first. Otherwise, we will run into a RecordNotUnique
exception when trying to add the same option_id to two duplicate
answers.

So we're making this task depend on the one that removes duplicate
answers. That means we no longer need to specify the task to remove
duplicate answers in the release tasks; it will automatically be
executed when running the task to add an option_id.

spec/lib/tasks/polls_spec.rb

@@ -120,4 +120,101 @@ describe "polls tasks" do
       end
     end
   end
+
+  describe "polls:populate_option_id" do
+    before do
+      Rake::Task["polls:remove_duplicate_answers"].reenable
+      Rake::Task["polls:populate_option_id"].reenable
+    end
+
+    it "populates the option_id column of existing answers when there's one valid answer" do
+      yes_no_question = create(:poll_question, :yes_no, poll: poll)
+      abc_question = create(:poll_question_multiple, :abc, poll: poll)
+      option_a = abc_question.question_options.find_by(title: "Answer A")
+      option_b = abc_question.question_options.find_by(title: "Answer B")
+
+      answer = create(:poll_answer, question: yes_no_question, author: user, answer: "Yes", option: nil)
+      abc_answer = create(:poll_answer, question: abc_question, author: user, answer: "Answer A", option: nil)
+      answer_with_inconsistent_option = create(:poll_answer, question: abc_question,
+                                                             author: user,
+                                                             answer: "Answer A",
+                                                             option: option_b)
+      answer_with_invalid_option = build(:poll_answer, question: abc_question,
+                                                       author: user,
+                                                       answer: "Non existing",
+                                                       option: nil)
+      answer_with_invalid_option.save!(validate: false)
+
+      Rake.application.invoke_task("polls:populate_option_id")
+      answer.reload
+      abc_answer.reload
+      answer_with_inconsistent_option.reload
+      answer_with_invalid_option.reload
+
+      expect(answer.option_id).to eq yes_no_question.question_options.find_by(title: "Yes").id
+      expect(abc_answer.option_id).to eq option_a.id
+      expect(answer_with_inconsistent_option.option_id).to eq option_b.id
+      expect(answer_with_invalid_option.option_id).to be nil
+    end
+
+    it "does not populate the option_id column when there are several valid options" do
+      question = create(:poll_question, title: "How do you pronounce it?")
+
+      create(:poll_question_option, question: question, title_en: "A", title_es: "EI")
+      create(:poll_question_option, question: question, title_en: "E", title_es: "I")
+      create(:poll_question_option, question: question, title_en: "I", title_es: "AI")
+
+      answer = create(:poll_answer, question: question, author: user, answer: "I", option: nil)
+
+      Rake.application.invoke_task("polls:populate_option_id")
+      answer.reload
+
+      expect(answer.option_id).to be nil
+    end
+
+    it "removes duplicate answers before populating the option_id column" do
+      user = create(:user, :level_two)
+      question = create(:poll_question_multiple, :abc)
+
+      answer_attributes = {
+        question_id: question.id,
+        author_id: user.id,
+        answer: "Answer A",
+        option_id: nil
+      }
+      answer = create(:poll_answer, answer_attributes)
+      insert(:poll_answer, answer_attributes)
+
+      answer.reload
+      expect(answer.option_id).to be nil
+
+      Rake.application.invoke_task("polls:populate_option_id")
+      answer.reload
+
+      expect(Poll::Answer.count).to eq 1
+      expect(answer.option_id).to eq question.question_options.find_by(title: "Answer A").id
+    end
+
+    it "populates the option_id column on tenants" do
+      create(:tenant, schema: "answers")
+
+      Tenant.switch("answers") do
+        question = create(:poll_question_multiple, :abc)
+
+        create(:poll_answer, question: question, answer: "Answer A", option: nil)
+      end
+
+      Rake.application.invoke_task("polls:populate_option_id")
+
+      Tenant.switch("answers") do
+        expect(Poll::Question.count).to eq 1
+        expect(Poll::Answer.count).to eq 1
+
+        question = Poll::Question.first
+        option_a = question.question_options.find_by(title: "Answer A")
+
+        expect(Poll::Answer.first.option_id).to eq option_a.id
+      end
+    end
+  end
 end