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Mastering Django: Core

You're reading from   Mastering Django: Core The Complete Guide to Django 1.8 LTS

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Product type Paperback
Published in Dec 2016
Publisher
ISBN-13 9781787281141
Length 694 pages
Edition 1st Edition
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Tools
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Author (1):
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Nigel George Nigel George
Author Profile Icon Nigel George
Nigel George
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Table of Contents (33) Chapters Close

Mastering Django: Core
Credits
About the Author
www.PacktPub.com
Preface
1. Introduction to Django and Getting Started FREE CHAPTER 2. Views and URLconfs 3. Templates 4. Models 5. The Django Admin Site 6. Forms 7. Advanced Views and URLconfs 8. Advanced Templates 9. Advanced Models 10. Generic Views 11. User Authentication in Django 12. Testing in Django 13. Deploying Django 14. Generating Non-HTML Content 15. Django Sessions 16. Djangos Cache Framework 17. Django Middleware 18. Internationalization 19. Security in Django 20. More on Installing Django 21. Advanced Database Management Model Definition Reference Database API Reference Generic View Reference Settings Built-in Template Tags and Filters Request and Response Objects Developing Django with Visual Studio

Deleting objects


The delete method, conveniently, is named delete(). This method immediately deletes the object and has no return value. Example:

e.delete() 

You can also delete objects in bulk. Every QuerySet has a delete() method, which deletes all members of that QuerySet.

For example, this deletes all Entry objects with a pub_date year of 2005:

Entry.objects.filter(pub_date__year=2005).delete() 

Keep in mind that this will, whenever possible, be executed purely in SQL, and so the delete() methods of individual object instances will not necessarily be called during the process. If you've provided a custom delete() method on a model class and want to ensure that it is called, you will need to manually delete instances of that model (for example, by iterating over a QuerySet and calling delete() on each object individually) rather than using the bulk delete() method of a QuerySet.

When Django deletes an object, by default it emulates the behavior of the SQL constraint ON DELETE CASCADE-in other words, any objects which had foreign keys pointing at the object to be deleted will be deleted along with it. For example:

b = Blog.objects.get(pk=1) 
# This will delete the Blog and all of its Entry objects. 
b.delete() 

This cascade behavior is customizable via the on_delete argument to the ForeignKey.

Note that delete() is the only QuerySet method that is not exposed on a Manager itself. This is a safety mechanism to prevent you from accidentally requesting Entry.objects.delete(), and deleting all the entries. If you do want to delete all the objects, then you have to explicitly request a complete query set:

Entry.objects.all().delete() 
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