Topic guide Making queries Related objectsOne-to-many relationships

In addition to the QuerySet methods defined in “Retrieving objects” above, the ForeignKey Manager has additional methods used to handle the set of related objects.

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Reference PostgreSQL specific model fields

Range fields support the standard lookups: lt, gt, lte and gte. These are not particularly helpful - they compare the lower bounds first and then the upper bounds only if necessary.

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Reference PostgreSQL specific model fields Range FieldsQuerying Range Fields

Range fields support the standard lookups: lt, gt, lte and gte. These are not particularly helpful - they compare the lower bounds first and then the upper bounds only if necessary.

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Topic guide Aggregation

Fields that are mentioned in the order_by() part of a queryset are used when selecting the output data, even if they are not otherwise specified in the values() call.

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Topic guide Database access optimization

To make use of the caching behavior of QuerySet, you may need to use the with template tag.

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Topic guide Making queries

Keyword argument queries – in filter(), etc. – are “AND”ed together. If you need to execute more complex queries (for example, queries with OR statements), you can use Q() objects.

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Topic guide Aggregation Generating aggregates for each item in a QuerySet

… most aggregates, there is no way to avoid this problem, however, the Count aggregate has a distinct parameter that may help: NOTE: In order to understand what happens in your query, consider inspecting the > query property of your QuerySet.

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Topic guide Making queries

Keyword argument queries – in filter(), etc. – are “AND”ed together. If you need to execute more complex queries (for example, queries with OR statements), you can use Q objects.

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Reference Form fields Fields which handle relationships

classModelMultipleChoiceField(**kwargs)[source] : - Default widget: SelectMultiple - Empty value: An empty QuerySet (self.queryset.none()) - Normalizes to: A QuerySet of model instances. - Validates that every id in the given list of values exists in the queryset.

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Topic guide Django shortcut functions

get_object_or_404(klass,*args,**kwargs)[source] aget_object_or_404(klass,*args,**kwargs) : Asynchronous version: aget_object_or_404()

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Index

… - quarter - field lookup type - query_pk_and_slug (django.views.generic.detail.SingleObjectMixin attribute) - query_string (django.views.generic.base.RedirectView attribute) - QueryDict (class in django.http) - queryset | - QuerySet (class in django.db.models.query) - queryset (django.views.generic.detail.SingleObjectMixin attribute) - (django.views.generic.list.MultipleObjectMixin attribute) - (ModelChoiceField attribute) - (ModelMultipleChoiceField attribute) …

Internals Django Deprecation Timeline

Calling QuerySet.values_list() with flat=True and no field name will raise TypeError. The use of None when querying a JSONField top-level value will compile to SQL IS NULL. Use JSONNull to query for a JSON null value instead.

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Reference Settings

Default: False Set this to True if you want to disable the use of server-side cursors with QuerySet.iterator(). Transaction pooling and server-side cursors describes the use case. This is a PostgreSQL-specific setting.

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Topic guide Aggregation

Ordinarily, annotations are generated on a per-object basis - an annotated QuerySet will return one result for each object in the original QuerySet.

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Topic guide

Article.objects.filter(publications__title__startswith="Science").distinct() <QuerySet [<Article: NASA uses Python>]> Reverse m2m queries are supported (i.e., starting at the table that doesn’t have a ManyToManyField): Excluding a related item works as you would expect, too (although the SQL involved is a little complex): If …

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Topic guide Database access optimization

When you have a lot of objects, the caching behavior of the QuerySet can cause a large amount of memory to be used. In this case, iterator() may help.

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Topic guide Making queries

To retrieve objects from your database, construct a QuerySet via a Manager on your model class. A QuerySet represents a collection of objects from your database. It can have zero, one or many filters.

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Topic guide Making queries

Sometimes you want to set a field to a particular value for all the objects in a QuerySet. You can do this with the update() method. For example: You can only set non-relation fields and ForeignKey fields using this method.

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Reference Settings Core SettingsDATABASES

Default: False Set this to True if you want to disable the use of server-side cursors with QuerySet.iterator(). Transaction pooling and server-side cursors describes the use case. This is a PostgreSQL-specific setting.

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Topic guide

Article.objects.filter(publications__title__startswith="Science").distinct() <QuerySet [<Article: NASA uses Python>]> Reverse m2m queries are supported (i.e., starting at the table that doesn’t have a ManyToManyField): Excluding a related item works as you would expect, too (although the SQL involved is a little complex): If …

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