Reference The sitemap framework

Here’s an example of a URLconf using GenericSitemap:

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Reference Django exceptions

exceptionObjectDoesNotExist[source] : The base class for Model.DoesNotExist exceptions. A try/except for ObjectDoesNotExist will catch DoesNotExist exceptions for all models.

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Reference Django exceptions

exceptionMultipleObjectsReturned[source] : The base class for Model.MultipleObjectsReturned exceptions. A try/except for MultipleObjectsReturned will catch MultipleObjectsReturned exceptions for all models.

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Reference Form fields

Two fields are available for representing relationships between models: ModelChoiceField and ModelMultipleChoiceField. Both of these fields require a single queryset parameter that is used to create the choices for the field.

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Reference Form fields

classModelChoiceField(**kwargs)[source] : - Default widget: Select - Empty value: None - Normalizes to: A model instance. - Validates that the given id exists in the queryset. - Error message keys: required, invalid_choice

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Reference Form fields

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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Reference Form fields

classModelChoiceIterator(field)[source] : The default class assigned to the iterator attribute of ModelChoiceField and ModelMultipleChoiceField. An iterable that yields 2-tuple choices from the queryset.

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Reference Form fields

classModelChoiceIteratorValue(value,instance)[source] : Two arguments are required:

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Reference Model class reference

exceptionModel.DoesNotExist : This exception is raised by the ORM when an expected object is not found. For example, QuerySet.get() will raise it when no object is found for the given lookups.

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Reference Conditional Expressions

classWhen(condition=None,then=None,**lookups)[source] A When() object is used to encapsulate a condition and its result for use in the conditional expression. Using a When() object is similar to using the filter() method.

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Reference Conditional Expressions

Let’s say we want to change the account_type for our clients to match their registration dates. We can do this using a conditional expression and the update() method:

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Reference Query Expressions

… directly: or they can be used to build a library of database functions: But both cases will result in a queryset where each model is annotated with an extra attribute field_lower produced, roughly, from the following SQL: See Database Functions …

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Reference Query Expressions

This is useful for specifying a value to be returned other than None when the queryset (or grouping) contains no entries. The **extra kwargs are key=value pairs that can be interpolated into the template attribute.

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Reference Query Expressions

To prevent a subquery from returning multiple rows, a slice ([:1]) of the queryset is used: In this case, the subquery must only return a single column and a single row: the email address of the most recently created comment.

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Reference Query Expressions

… returns a boolean value and Exists() may be used as a condition in When expressions, or to directly filter a queryset: This will ensure that the subquery will not be added to the SELECT columns, which may result in a …

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Reference Query Expressions

values('post') aggregates comments by Post. Finally, annotate(...) performs the aggregation. The order in which these queryset methods are applied is important. In this case, since the subquery must be limited to a single column, values('total') is required.

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Reference Model instance reference

If you delete a field from a model instance, accessing it again reloads the value from the database: Model.refresh_from_db(using=None,fields=None,from_queryset=None)[source] Model.arefresh_from_db(using=None,fields=None,from_queryset=None) Asynchronous version: arefresh_from_db() If you need to reload a model’s values from the database, you can use the refresh_from_db() method.

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Reference Signals

django.db.models.signals.pre_delete Sent at the beginning of a model’s delete() method and a queryset’s delete() method. Arguments sent with this signal: sender The model class. instance The actual instance being deleted. using The database alias being used.

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Reference Signals

django.db.models.signals.post_delete Like pre_delete, but sent at the end of a model’s delete() method and a queryset’s delete() method. Arguments sent with this signal: sender : The model class. instance : The actual instance being deleted.

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Topic guide Asynchronous support

With some exceptions, Django can run ORM queries asynchronously: Detailed notes can be found in Asynchronous queries, but in short: All QuerySet methods that cause an SQL query to occur have an a-prefixed asynchronous variant.

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