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Is it possible to test if a single model instance satisfies the conditions of a Q object? So, is there a function like is_q_satisified:

article = Article.objects.filter(title='Foo')[0]
q = Q(title='Foo')
assert is_q_satisfied(q, article)
Tomasz Jakub Rup
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Kyrios Kivdilos
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1 Answers1

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There isn't a built in is_q_satisified, but you can make one yourself, by filtering on the q and the object's primary key.

# Note I've used get() to return an object, 
# instead of filter(), which returns a queryset.
article = Article.objects.get(title='Foo')

def is_q_satisfied(obj, q):
    return type(obj).objects.filter(q).filter(pk=obj.pk).exists()

q = Q(title='Foo')
is_q_satisfied(article, q)
Ali Shamakhi
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Alasdair
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  • So this works for a single model instance? And also, will the `exists()` call result in a call to the database? – Kyrios Kivdilos Oct 01 '15 at 13:28
  • Yes, it works for a single instance, and yes, it results in a call to the db. My method is a quick hack, that relies on a database query to do the hard work. I think it would be possible to do it without the database lookup, but much harder. `Q(title='Foo').children` returns the list `[('title', 'foo')]` and you can check `getattr(obj, 'title') == 'Foo'`, but the code would then get more complicated as Q objects can be combined, and you can get lookups like `Q(category__title='Bar')`. – Alasdair Oct 01 '15 at 13:39
  • This is fine, but it makes a database query. I was wondering if there is a way to test the model instance against a Q object without making a database query? It is possible by parsing the content of the Q object and translating it to relevant assertions on the model instance, but that would be reinventing the wheel IMO! – Ali Shamakhi Jan 22 '22 at 08:26
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    @AliShamakhi it would be possible to test some assertions in Python, e.g. `Q(published=False)`, but there are others that require database lookups, e.g. `Q(author__name='Ali')`, which is filtering on a related model. – Alasdair Jan 22 '22 at 10:24