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I have a query that requires to filter exactly 2 authors with the ID
Theoretically,
Book.objects.filter(author__id=1, author__id=2). which is not possible.
How can I solve this problem?
Cheers, Mickey
512
_set is associated with reverse relation on a model. Django allows you to access reverse relations on a model. By default, Django creates a manager ( RelatedManager ) on your model to handle this, named <model>_set, where <model> is your model name in lowercase.
Return Specific Columns The values_list() method allows you to return only the columns that you specify.
Use Django's count() QuerySet method — simply append count() to the end of the appropriate QuerySet. Generate an aggregate over the QuerySet — Aggregation is when you "retrieve values that are derived by summarizing or aggregating a collection of objects." Ref: Django Aggregation Documentation.
Not intuitive at first but the answer is right in front of us.
Book.objects.filter(author__id=1).filter(author__id=2) If you want an exact match, you could potentially further filter this result by those items that only have exactly 2 authors.
Book.objects.annotate(count=Count('author')).filter(author__id=1)\ .filter(author__id=13).filter(count=2) If you want exact matches dynamically, how about something like this?:
def get_exact_match(model_class, m2m_field, ids): query = model_class.objects.annotate(count=Count(m2m_field))\ .filter(count=len(ids)) for _id in ids: query = query.filter(**{m2m_field: _id}) return query matches = get_exact_match(MyModel, 'my_m2m_field', [1, 2, 3, 4]) # matches is still an unevaluated queryset, so you could run more filters # without hitting the database. If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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