According to the documentation, you should use:
from django.db.models import Count
Transaction.objects.all().values('actor').annotate(total=Count('actor')).order_by('total')
values() : specifies which columns are going to be used to “group by”
Django docs:
“When a values() clause is used to constrain the columns that are
returned in the result set, the method for evaluating annotations is
slightly different. Instead of returning an annotated result for each
result in the original QuerySet, the original results are grouped
according to the unique combinations of the fields specified in the
values() clause”
annotate() : specifies an operation over the grouped values
Django docs:
The second way to generate summary values is to generate an independent summary for each object in a QuerySet. For example, if you
are retrieving a list of books, you may want to know how many authors
contributed to each book. Each Book has a many-to-many relationship
with the Author; we want to summarize this relationship for each book
in the QuerySet.Per-object summaries can be generated using the annotate() clause.
When an annotate() clause is specified, each object in the QuerySet
will be annotated with the specified values.
The order by clause is self explanatory.
To summarize: you group by, generating a queryset of authors, add the annotation (this will add an extra field to the returned values) and finally, you order them by this value
Refer to https://docs.djangoproject.com/en/dev/topics/db/aggregation/ for more insight
Good to note: if using Count, the value passed to Count does not affect the aggregation, just the name given to the final value. The aggregator groups by unique combinations of the values (as mentioned above), not by the value passed to Count. The following queries are the same:
Transaction.objects.all().values('actor').annotate(total=Count('actor')).order_by('total')
Transaction.objects.all().values('actor').annotate(total=Count('id')).order_by('total')