I have the following code which takes an existing instance and copies, or 'archives' it, in another model and then deletes it replacing it with the draft copy.

Current Code

def archive_calc(self, rev_num, primary_field):model_a = Calc.objects.get(tag_number__tag_number = primary_field, revision_number = rev_num) #Current Revision instancemodel_b = CalcArchive() #Draft instance#Copies data to archive modelfor field in model_a._meta.fields:setattr(model_b, field.name, getattr(model_a, field.name))model_b.pk = Nonemodel_b.current_revision = Falsemodel_b.save()model_a.delete()

This works fine however i need to change the system to allow for certain models with foreign keys as when an instance is archived/deleted the related records are deleted along with it. So my idea to fix this is to have the changes from the draft record copied to the previous record and then have the draft deleted thus maintaining the foreign key related records.

Solution idea

def archive_calc(self, rev_num, primary_field):model_a = Calc.objects.get(tag_number__tag_number = primary_field, revision_number = rev_num) #Current Revision instancemodel_b = CalcArchive() #Archive Instancemodel_c = Calc.objects.get(pk = self.object.pk) #Draft instance#Copies data to archive modelfor field in model_a._meta.fields:setattr(model_b, field.name, getattr(model_a, field.name))model_b.pk = Nonemodel_b.current_revision = Falsemodel_b.save()#Copies data from draft instance to current revision instancefor field in model_c._meta.fields:setattr(model_a, field.name, getattr(model_c, field.name))model_c.delete()

Unfortunately the above solution doesn't work, it just seems to ignore the copy and continues to work as per 'Current Code'. If I add model_a.save() after for field in model_c._meta.fi... the system gets stuck in a loop and eventually throws maximum recursion depth exceeded in cmp.

Any help would be much appreciate as usual and if im barking up the wrong tree please let me know.

After alot of poking around and reading the Django docs I have come up with what seems to be a pretty nice, simple solution.

def archive_calc(self, rev_num, primary_field):model_a = Calc.objects.get(calc_details__calc_serial_number = primary_field, revision_number = rev_num)model_b = CalcArchive()object_list_annual = model_a.calcreview_set.filter(calc__calc_details = primary_field)object_list_ageing = model_a.calcitem_set.filter(calc__calc_details = primary_field)for obj in object_list_annual:obj.calc_id = self.object.idobj.save()for obj in object_list_ageing:obj.calc_id = self.object.idobj.save()for field in model_a._meta.fields:setattr(model_b, field.name, getattr(model_a, field.name))model_b.pk = Nonemodel_b.current_revision = Falsemodel_b.save()model_a.delete()

This 'moves' the related objects by setting the _id fields to the same as self.object.id.

Ive ran several tests and this seems to achieve exactly what I was looking for with minimal code and no extra installs.

Hope this helps someone and please feel free to point out any potential pitfalls in my answer.