TMSS-215: PROTECT against deletion

SAS/TMSS/src/tmss/tmssapp/models/specification.py

@@ -389,7 +389,7 @@ class SchedulingUnitDraft(NamedCommon):
     generator_instance_doc = JSONField(null=True, help_text='Parameter value that generated this run draft (NULLable).')
     scheduling_set = ForeignKey('SchedulingSet', related_name='scheduling_unit_drafts', on_delete=CASCADE, help_text='Set to which this scheduling unit draft belongs.')
     requirements_template = ForeignKey('SchedulingUnitTemplate', on_delete=CASCADE, help_text='Schema used for requirements_doc.')
-    observation_strategy_template = ForeignKey('SchedulingUnitObservingStrategyTemplate', on_delete=CASCADE, null=True, help_text='Observation Strategy Template used to create the requirements_doc.')
+    observation_strategy_template = ForeignKey('SchedulingUnitObservingStrategyTemplate', on_delete=PROTECT, null=True, help_text='Observation Strategy Template used to create the requirements_doc.')
 
     def save(self, force_insert=False, force_update=False, using=None, update_fields=None):
         if self.requirements_doc: