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Two Scoops of Django / Model
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tim
November 28, 2013
2
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Two Scoops of Django / Model
this is my presentation about two scoops of django's chapter 6
tim
November 28, 2013
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Transcript
django model
Recap class SafeUser(models.Model): ! user = models.OneToOneField(User,related_name='safe_user') display_name = models.CharField(null=True,
blank=True, max_length=1024) ! def __unicode__(self): return self.user.username + ' ' + self.display_name
Outline • Good Packages • Model Inheritance • South Experiences
• secret behind fields’ parameter
recommended package • south • django-model-util • django extension
South • Existing Database need another command to alter the
table • South do it for you. • https://docs.djangoproject.com/en/dev/releases/ 1.7/ <— syncdb will be deprecated
shell_plus • command from djagno extension
django-model-util • STATUS model • Field Tracker ( previous value
of your model)
Basic • How much Model in an app is appropriate
• Can I write raw SQL? • Can I add index?
Model Inheritance
Situations of Inheritance • Share Common Parts • Reuse Table
• Add Extra Ability
share Common Part ! • Base Class will not be
a table • share common fields between table class CommonInfo(models.Model): name = models.CharField(max_length=100) age = models.PositiveIntegerField() ! class Meta: abstract = True
multi-table inheritance • Just inherit • will create two table
• implicitly using foreign key from django.db import models ! class Place(models.Model): name = models.CharField(max_length=50) address = models.CharField(max_length=80) ! class Restaurant(Place): serves_hot_dogs = models.BooleanField() serves_pizza = models.BooleanField()
Proxy Model • No Extra Table • add more function
class Person(models.Model): first_name = models.CharField(max_length=30) last_name = models.CharField(max_length=30) ! class MyPerson(Person): class Meta: proxy = True ! def do_something(self): # ... pass
South Issue • After you finish your first version of
django app • python manage.py schemamigration app — initial • add migration test if possible
normalize? • denormalized carefully
Concern Cache • Concern Cache first. than the De-normalize •
CH20 discuss more about reducing bottle neck
Fields • Blank is logical, for validation • null is
related to how database save empty value • any field without null=True specified in the model needs to have a value set (from Malcolm)
None
Manager • Looking very good • More Readable
You have two choice
the reason • First manager will be used by django
Summary • Start normalized • Don’t forget to use indexes.
• Watch out for the “gotchas” when using the null=True and blank=True • model inheritance