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| -rw-r--r-- | docs/ref/models/querysets.txt | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/docs/ref/models/querysets.txt b/docs/ref/models/querysets.txt index 1b3f703bdf..ff750dd457 100644 --- a/docs/ref/models/querysets.txt +++ b/docs/ref/models/querysets.txt @@ -1245,6 +1245,26 @@ where prefetching with a custom ``QuerySet`` is useful: >>> restaurants = Restaurant.objects.prefetch_related( ... Prefetch('best_pizza', queryset=queryset)) +When using multiple databases, ``Prefetch`` will respect your choice of +database. If the inner query does not specify a database, it will use the +database selected by the outer query. All of the following are valid:: + + >>> # Both inner and outer queries will use the 'replica' database + >>> Restaurant.objects.prefetch_related('pizzas__toppings').using('replica') + >>> Restaurant.objects.prefetch_related( + ... Prefetch('pizzas__toppings'), + ... ).using('replica') + >>> + >>> # Inner will use the 'replica' database; outer will use 'default' database + >>> Restaurant.objects.prefetch_related( + ... Prefetch('pizzas__toppings', queryset=Toppings.objects.using('replica')), + ... ) + >>> + >>> # Inner will use 'replica' database; outer will use 'cold-storage' database + >>> Restaurant.objects.prefetch_related( + ... Prefetch('pizzas__toppings', queryset=Toppings.objects.using('replica')), + ... ).using('cold-storage') + .. note:: The ordering of lookups matters. @@ -3655,6 +3675,10 @@ lookups or :class:`Prefetch` objects you want to prefetch for. For example:: >>> restaurants = fetch_top_restaurants_from_cache() # A list of Restaurants >>> prefetch_related_objects(restaurants, 'pizzas__toppings') +When using multiple databases with ``prefetch_related_objects``, the prefetch +query will use the database associated with the model instance. This can be +overridden by using a custom queryset in a related lookup. + ``FilteredRelation()`` objects ------------------------------ |