#2114 repeating query in django view

[Pokapiec]

What does this pull request do?

In this PR i add another condition to elif statement in utils.encoding.transform function to handle displaying representation of django QuerySet object in custom way. We need to do it because if we try to execute repr function on unexecuted QuerySet which causes Timeout on database, it will execute by utils.encoding.transform function.

I also added a simple test simulating database Timeout.

By overwriting _result_cache on django QuerySet object we ensure that django will not try to execute any query to db.

Related issues

Closes #2114

[cla-checker-service]

💚 CLA has been signed

[Pokapiec]

@xrmx this is the PR i created to resolve this issue #2114 we discussed earlier. I wanted to add this transformation logic to django contrib code but i couldn't make it work so i had to move it to transform func. Let me know if there is a better way.

[gtback]

cla/check

[xrmx]

I think we shouldn't poke much with Django internals, also we should not assume django is installed

[xrmx]

Suggested change

	elif isinstance(value, QuerySet):
	value._result_cache = []
	ret = repr(value)
	elif DjangoQuerySet is not None and isinstance(value, DjangoQuerySet) and getattr(value, "_result_cache", True) is None:
	# if we have a Django QuerySet a None result cache it may mean that the underlying query failed
	# so represent it as an empty list instead of retrying the query again
	ret = "<%s %r>" % (value.__class__.__name__, [])

Instead of erasing the values everytime shouldn't we just do something is value._result_cache is None?

[pawelusermoc]

sure, there is a little less magic to your solution 👌

[xrmx]

Suggested change

	from django.db.models import QuerySet
	try:
	from django.db.models import QuerySet as DjangoQuerySet
	except ImportError:
	DjangoQuerySet = None

[pawelusermoc]

good point i will change it 👌