Job warnings have to be deleted explicitly (#4175)

For the reasoning, see comment in PollableJobCleanup.

Author: philippthun

app/jobs/runtime/pollable_job_cleanup.rb

@@ -9,10 +9,30 @@ def initialize(cutoff_age_in_days)
         end
 
         def perform
-          old_pollable_jobs = PollableJobModel.where(Sequel.lit("created_at < CURRENT_TIMESTAMP - INTERVAL '?' DAY", cutoff_age_in_days))
           logger = Steno.logger('cc.background.pollable-job-cleanup')
+          cutoff_condition = Sequel.lit("created_at < CURRENT_TIMESTAMP - INTERVAL '?' DAY", cutoff_age_in_days)
+
+          old_pollable_jobs = PollableJobModel.where(cutoff_condition)
           logger.info("Cleaning up #{old_pollable_jobs.count} Jobs rows")
           old_pollable_jobs.delete
+
+          # Job warnings have to be deleted explicitly, because
+          # - we don't have a foreign key constraint and thus cannot use DELETE CASCADE, and
+          # - we don't delete/destroy pollable job model objects one by one and thus cannot use hooks defined by the
+          #   'destroy' association dependency between PollableJobModel and JobWarningModel.
+          # Instead, we delete all expired jobs with a single SQL statement.
+          #
+          # By using the same cutoff condition based on 'created_at' for pollable jobs and job warnings, we ensure that
+          # only job warnings are deleted where it is guaranteed that also the associated pollable job already has been
+          # removed. This is due to the fact that job warnings are created after their associated pollable job, i.e.
+          # pollable_job.created_at <= job_warning.created_at.
+          #
+          # On the other hand, it is not guaranteed that all associated job warnings are deleted for all pollable jobs
+          # that have been removed during an execution of this cleanup job. But these leftovers will simply be removed
+          # during the next job execution.
+          old_job_warnings = JobWarningModel.where(cutoff_condition)
+          logger.info("Cleaning up #{old_job_warnings.count} Job Warnings rows")
+          old_job_warnings.delete
         end
 
         def job_name_in_configuration

spec/unit/jobs/runtime/pollable_job_cleanup_spec.rb

@@ -6,7 +6,9 @@ module Jobs::Runtime
       let(:cutoff_age_in_days) { 30 }
       subject(:job) { PollableJobCleanup.new(cutoff_age_in_days) }
       let!(:old_job) { PollableJobModel.create(created_at: (cutoff_age_in_days + 1).days.ago) }
+      let!(:old_warning) { JobWarningModel.create(job: old_job, created_at: old_job.created_at, detail: 'some warning') }
       let!(:new_job) { PollableJobModel.create(created_at: (cutoff_age_in_days - 1).day.ago) }
+      let!(:new_warning) { JobWarningModel.create(job: new_job, created_at: new_job.created_at, detail: 'some warning') }
 
       it { is_expected.to be_a_valid_job }
 
@@ -23,6 +25,12 @@ module Jobs::Runtime
       it 'knows its job name' do
         expect(job.job_name_in_configuration).to equal(:pollable_job_cleanup)
       end
+
+      it 'also deletes associated warnings' do
+        job.perform
+        expect(JobWarningModel.find(id: old_warning.id)).to be_nil
+        expect(JobWarningModel.find(id: new_warning.id)).to eq(new_warning)
+      end
     end
   end
 end