Error while using pghistory.BeforeDelete() of django-pghistory - django

Question

I am using django-pghistory 1.2.0 to keep my changes using postgres triggers. For insert or update, it saves data to event table for both ORM and raw queries. But while using delete, it throws errors.
My model:
#pghistory.track(
pghistory.AfterInsert('after_insert'),
pghistory.AfterUpdate('after_update'),
pghistory.BeforeDelete('before_delete')
)
class TestModel(models.Model):
int_field = models.IntegerField()
char_field = models.CharField(max_length=16)
Error:
psycopg2.errors.ObjectNotInPrerequisiteState: record "new" is not assigned yet
DETAIL: The tuple structure of a not-yet-assigned record is indeterminate.
CONTEXT: SQL statement "INSERT INTO "loan_mngmt_app_testmodelevent"
("int_field", "char_field", "id", "pgh_created_at", "pgh_label", "pgh_obj_id", "pgh_context_id") VALUES (OLD."int_field", OLD."char_field", OLD."id", NOW(), 'before_delete', NEW."id", _pgh_attach_context())"
PL/pgSQL function pgtrigger_before_delete_f0f49() line 14 at SQL statement
django.db.utils.OperationalError: record "new" is not assigned yet
DETAIL: The tuple structure of a not-yet-assigned record is indeterminate.
CONTEXT: SQL statement "INSERT INTO "loan_mngmt_app_testmodelevent"
("int_field", "char_field", "id", "pgh_created_at", "pgh_label", "pgh_obj_id", "pgh_context_id") VALUES (OLD."int_field", OLD."char_field", OLD."id", NOW(), 'before_delete', NEW."id", _pgh_attach_context())"
PL/pgSQL function pgtrigger_before_delete_f0f49() line 14 at SQL statement
Test API for CRUD operation:
class TestModelAPI(APIView):
def post(self, request, *args, **kwargs):
obj = TestModel.objects.create(int_field=1, char_field='c1')
obj.int_field = 2
obj.char_field = 'c2'
obj.save()
obj.delete()
return JsonResponse(
data={'message': 'success'},
status=200,
)
My INSTALLED_APPS:
INSTALLED_APPS = [
.............,
'pgtrigger',
'pgconnection',
'pghistory',
]
My database settings:
DATABASES = pgconnection.configure({
"default": {
"ENGINE": "django.db.backends.postgresql",
"NAME": "<some-value>",
"USER": "<some-value>",
"PASSWORD": "<some-value>",
"HOST": "<some-value>",
"PORT": "<some-value>",
},
})
Details error:
Traceback (most recent call last):
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 84, in _execute
return self.cursor.execute(sql, params)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/pgconnection/core.py", line 85, in execute
return super().execute(sql, args)
psycopg2.errors.ObjectNotInPrerequisiteState: record "new" is not assigned yet
DETAIL: The tuple structure of a not-yet-assigned record is indeterminate.
CONTEXT: SQL statement "INSERT INTO "loan_mngmt_app_testmodelevent"
("int_field", "char_field", "id", "pgh_created_at", "pgh_label", "pgh_obj_id", "pgh_context_id") VALUES (OLD."int_field", OLD."char_field", OLD."id", NOW(), 'before_delete', NEW."id", _pgh_attach_context())"
PL/pgSQL function pgtrigger_before_delete_f0f49() line 14 at SQL statement
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/django/core/handlers/exception.py", line 47, in inner
response = get_response(request)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/django/core/handlers/base.py", line 179, in _get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
return view_func(*args, **kwargs)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/django/views/generic/base.py", line 70, in view
return self.dispatch(request, *args, **kwargs)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/rest_framework/views.py", line 509, in dispatch
response = self.handle_exception(exc)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/rest_framework/views.py", line 469, in handle_exception
self.raise_uncaught_exception(exc)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/rest_framework/views.py", line 480, in raise_uncaught_exception
raise exc
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/rest_framework/views.py", line 506, in dispatch
response = handler(request, *args, **kwargs)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/loan_mngmt_app/api/client_data_api.py", line 88, in post
obj.delete()
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/django/db/models/base.py", line 947, in delete
return collector.delete()
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/django/db/models/deletion.py", line 396, in delete
count = sql.DeleteQuery(model).delete_batch([instance.pk], self.using)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/django/db/models/sql/subqueries.py", line 43, in delete_batch
num_deleted += self.do_query(self.get_meta().db_table, self.where, using=using)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/django/db/models/sql/subqueries.py", line 23, in do_query
cursor = self.get_compiler(using).execute_sql(CURSOR)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 1156, in execute_sql
cursor.execute(sql, params)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 98, in execute
return super().execute(sql, params)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 66, in execute
return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 75, in _execute_with_wrappers
return executor(sql, params, many, context)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 84, in _execute
return self.cursor.execute(sql, params)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/django/db/utils.py", line 90, in __exit__
raise dj_exc_value.with_traceback(traceback) from exc_value
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 84, in _execute
return self.cursor.execute(sql, params)
File "/media/arif/74809FD62472EDA3/SourceCode/tkdc/venv/lib/python3.6/site-packages/pgconnection/core.py", line 85, in execute
return super().execute(sql, args)
django.db.utils.OperationalError: record "new" is not assigned yet
DETAIL: The tuple structure of a not-yet-assigned record is indeterminate.
CONTEXT: SQL statement "INSERT INTO "loan_mngmt_app_testmodelevent"
("int_field", "char_field", "id", "pgh_created_at", "pgh_label", "pgh_obj_id", "pgh_context_id") VALUES (OLD."int_field", OLD."char_field", OLD."id", NOW(), 'before_delete', NEW."id", _pgh_attach_context())"
PL/pgSQL function pgtrigger_before_delete_f0f49() line 14 at SQL statement
What wrong i have done to configure pghistory.BeforeDelete() of django-pghistory and what is the solution of this problem?

Answer 1

The solution is to use obj_fk=None to pghistory.track()
#pghistory.track(
pghistory.AfterInsert('after_insert'),
pghistory.AfterUpdate('after_update'),
pghistory.BeforeDelete('before_delete'),
obj_fk=None
)
class TestModel(models.Model):
int_field = models.IntegerField()
char_field = models.CharField(max_length=16)
Without obj_fk=None, The trigger will be created where pgh_obj_id column will be present and it will be populated via NEW."id" into trigger's insert statement which raises the error.
CREATE OR REPLACE FUNCTION public.pgtrigger_before_delete_f0f49()
RETURNS trigger
LANGUAGE plpgsql
AS $function$
BEGIN
IF (_pgtrigger_should_ignore(TG_TABLE_NAME, TG_NAME) IS TRUE) THEN
IF (TG_OP = 'DELETE') THEN
RETURN OLD;
ELSE
RETURN NEW;
END IF;
END IF;
INSERT INTO "loan_mngmt_app_testmodelevent"
("int_field", "char_field", "id", "pgh_created_at", "pgh_label", "pgh_obj_id", "pgh_context_id") VALUES (OLD."int_field", OLD."char_field", OLD."id", NOW(), 'before_delete', NEW."id", _pgh_attach_context());
RETURN NULL;
END;
$function$
;
After using obj_fk=None, you run make migration and migrate command which will remove pgh_obj_id column and NEW."id" from the insert statement.
New statement will be this:
CREATE OR REPLACE FUNCTION public.pgtrigger_before_delete_f0f49()
RETURNS trigger
LANGUAGE plpgsql
AS $function$
BEGIN
IF (_pgtrigger_should_ignore(TG_TABLE_NAME, TG_NAME) IS TRUE) THEN
IF (TG_OP = 'DELETE') THEN
RETURN OLD;
ELSE
RETURN NEW;
END IF;
END IF;
INSERT INTO "loan_mngmt_app_testmodelevent"
("int_field", "char_field", "id", "pgh_created_at", "pgh_label", "pgh_context_id") VALUES (OLD."int_field", OLD."char_field", OLD."id", NOW(), 'before_delete', _pgh_attach_context());
RETURN NULL;
END;
$function$
;