The Django Book - Chapter 5: Models slides for http://django-book.readthedocs.org/en/latest/index.html

1. The Django Book—Models
Sharre Chen
http://django-book.readthedocs.org/en/latest/index.html

2. The “Dumb” Way to Do Database Queries
in Views

3. Django’s database API

4. MVC
M(Model): data access logic, is handled by
Django’s database layer
V(View): business logic, is handled by views and
templates.
C(Controller): presentation logic, is handled by the
framework itself by following your URLconf and
calling the appropriate Python function.

5. MTV
M(Model): data access layer.
T(Template): the presentation layer.
V(View): business logic layer.

6. Configuring the Database
• In settings.py:
Example for MySQL:
DATABASE_ENGINE = 'mysql'
DATABASE_NAME = 'mydb'
DATABASE_USER= 'user'
DATABASE_PASSWORD = 'password'
DATABASE_HOST = ‘/var/run/mysql'
!
Try if setting is correct:
$ python manage.py shell
>>> from django.db import connection
>>> cursor = connection.cursor()

7. What’s the difference between a project and
an app?
• A project is an instance of a certain set of Django
apps, plus the configuration for those apps.
• An app is a portable set of Django functionality,
usually including models and views, that lives
together in a single Python package.
★if you’re using Django’s database layer (models),
you must create a Django app.

8. Create an app
create a books app:
$ python manage.py startapp books
file structure will look like:

9. Data access with Django

10. Installing the Model
Edit setting.py file again:
!
!
!
!

11. Check models’ syntax
checks whether your models’ syntax and logic are
correct:
$ python manage.py validate

12. check create table sql
If your models are valid, run the following command
for Django to generate CREATE TABLE statements
for your models in the books app (before migration):
$ python manage.py sqlall books

13. commit the SQL to database
$ python manage.py syncdb
!
!
★ Note that syncdb does not sync changes
in models or deletions of models.

14. Basic data access
Try it out:
$ python manage.py shell

15. Basic data access
If you want to create an object and save it to
the database in a single step, use the
objects.create() method.

16. Adding Model String Representations
it difficult to tell the Publisher objects apart:

17. Inserting and Updating Data
update name:
will result in:

18. Selecting Objects
if you type command:
This roughly translates to this SQL:
!
✦ Zen of Python: “Explicit is better than
implicit.”

19. Filtering Data
filter data:
This roughly translates to this SQL:
!

20. Filtering Data: LIKE
filter data:
!
here, the __contains part gets translated by
Django into a SQL LIKE statement:
!

21. Retrieving Single Objects
get single data:
will result in:
!
!
you may write:

22. Ordering Data
get ordered data:
SQL will be:
!
To order by multiple fields:
!
specify reverse ordering:

23. Ordering Data
Specify a default ordering in model:

24. Chaining Lookups
get filtered and ordered data:
!
As SQL:

25. Slicing Data
get first ordered data:
!
As SQL:

26. Slicing Data
but can not do:
!
!
you can do in another way:

27. Updating Multiple Objects in One Statement
update a filed:
!
!
update will return success updated object number:

28. Deleting Objects
delete a data:
!
!
delete all matched data:

29. Q&A
Thank You ~ :)