Reference

> > If you use [`prefetch_related()`](querysets.md#django.db.models.query.QuerySet.prefetch_related), > the `add()`, `aadd()`, `remove()`, `aremove()`, `clear()`, > `aclear()`, `set()`, and `aset()` methods clear the prefetched > cache.

Topic guide

To define a many-to-many relationship, use ManyToManyField.

Topic guide

… to deleted publications will no longer be included in the related entries: Bulk delete some articles - references to deleted objects should go: After the delete(), the QuerySet cache needs to be cleared, and the referenced objects should be gone:

Topic guide

Article.objects.filter(reporter__first_name="John") <QuerySet [<Article: John's second story>, <Article: This is a test>]> Query twice over the related field.

Topic guide Models Model methods

NOTE: Note that the delete() method for an object is not > necessarily called when deleting objects in bulk using a > QuerySet or as a result of a cascading > delete.

Topic guide Making queries

To represent database-table data in Python objects, Django uses an intuitive system: A model class represents a database table, and an instance of that class represents a particular record in the database table.

Topic guide Making queries Retrieving objectsLookups that span relationships

When spanning a ManyToManyField or a reverse ForeignKey (such as from Blog to Entry), filtering on multiple attributes raises the question of whether to require each attribute to coincide in the same related object.

Topic guide Making queries Related objectsOne-to-many relationships

Subsequent accesses to the foreign key on the same object instance are cached. Example: Note that the select_related() QuerySet method recursively prepopulates the cache of all one-to-many relationships ahead of time. Example:

Topic guide Making queries Related objectsMany-to-many relationships

You would expect it to return the entry e. However, the filter condition, which traverses the many-to-many relationship between Entry and Author, yields an empty QuerySet.

Topic guide Pagination

… you methods for accessing the items for each page: NOTE: Note that you can give Paginator a list/tuple, a Django QuerySet, > or any other object with a count() or __len__() method. When > determining the number of objects contained …

Index

| | | | --- | --- | | - handle() (BaseCommand method) - handle_app_config() (AppCommand method) - handle_label() (LabelCommand method) - handle_no_permission() (AccessMixin method) - handle_raw_input() (FileUploadHandler method) - handler400 (in module django.conf.urls) - handler403 (in module django.conf.urls) - …

Index

| | | | --- | --- | | - m (LineString attribute) - (Point attribute) - mail_admins() (in module django.core.mail) - mail_managers() (in module django.core.mail) - make_aware() (in module django.utils.timezone) - make_list - template filter - make_naive() (in module …

How-to How to write custom lookups

You will need to ensure that this registration happens before you try to create any querysets using it. You could place the implementation in a models.py file, or register the lookup in the ready() method of an AppConfig.

Reference The Django admin site ModelAdmin objects

ModelAdmin.save_as : Set save_as to enable a “save as new” feature on admin change forms. ModelAdmin.save_as_continue : When save_as=True, the default redirect after saving the new object is to the change view for that object.

Reference The syndication feed framework The high-level framework

This simple example, taken from a hypothetical police beat news site describes a feed of the latest five news items: To connect a URL to this feed, put an instance of the Feed object in your URLconf.

Reference Model instance reference

In addition to save(), delete(), a model object might have some of the following methods: Model.get_FOO_display() For every field that has choices set, the object will have a get_FOO_display() method, where FOO is the name of the field.

Topic guide Making queries Retrieving objects

Django offers a powerful and intuitive way to “follow” relationships in lookups, taking care of the SQL JOINs for you automatically, behind the scenes.

Topic guide Making queries Querying JSONField

As with other fields, storing None as the field’s value will store it as SQL NULL. While not recommended, it is possible to store JSON scalar null instead of SQL NULL by using Value(None, JSONField()).

Topic guide Making queries Querying JSONField

To query based on a given dictionary key, use that key as the lookup name: Multiple keys can be chained together to form a path lookup: If the key is an integer, it will be interpreted as an index transform …

… Model index reference Constraints reference Model _meta API Related objects reference Model class reference Model Meta options Model instance reference QuerySet API reference Lookup API reference Query Expressions Conditional Expressions Database Functions Paginator Paginator class AsyncPaginator class Page class AsyncPage …