queryset.count() is less efficient than checking
queryset.exists(), so use
querySet.count() if you only want the count, and use
queryset.exists() if you only want to find out if at least one result exists.
queryset.count() performs an SQL operation that scans every row in the database table.
queryset.exists() simply reads a single record in the most optimized way (removing ordering, clearing any user-defined
This is especially relevant for Postgres because
count() can be very expensive.
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