1. Advanced Models
「The Django Book」 Chapter 10
Spin Lai
July 23, 2013
2013年7月24日星期三

2. 賴司平 (Spin)
資拓宏宇 氣象科技事業處
PHP、Javascript、Python
About me
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3. Related objects
Update database schema
Model methods
Managers
Execute raw SQL queries
More about Managers
Today’s topics
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4. Related objects
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5. Recalling the
Chapter 5 ...
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6. Publisher
id
name
address
city
state_province
country
website
AutoField
CharField
CharField
CharField
CharField
CharField
URLField
Book
id
title
authors
publisher
publication_date
AutoField
CharField
ManyToManyField
ForeignKey
DateField
Author
id
first_name
last_name
email
AutoField
CharField
CharField
EmailField
N:1N:M
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7. class Publisher(models.Model):
name = models.CharField(max_length=30)
address = models.CharField(max_length=50)
city = models.CharField(max_length=60)
state_province = models.CharField(max_length=30)
country = models.CharField(max_length=50)
website = models.URLField()
def __unicode__(self):
return self.name
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8. class Author(models.Model):
first_name = models.CharField(max_length=30)
last_name = models.CharField(max_length=40)
email = models.EmailField()
def __unicode__(self):
return u'%s %s' % (self.first_name,
self.last_name)
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9. class Book(models.Model):
title = models.CharField(max_length=100)
authors = models.ManyToManyField(Author)
publisher = models.ForeignKey(Publisher)
publication_date = models.DateField()
def __unicode__(self):
return self.title
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10. class Book(models.Model):
title = models.CharField(max_length=100)
authors = models.ManyToManyField(Author)
publisher = models.ForeignKey(Publisher)
publication_date = models.DateField()
def __unicode__(self):
return self.title
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11. Foreign Key Value
Publisher
id
name
address
city
state_province
country
website
AutoField
CharField
CharField
CharField
CharField
CharField
URLField
Book
id
title
authors
publisher
AutoField
CharField
ManyToManyField
ForeignKey
>>> b = Book.objects.get(id=50)
>>> b.publisher
<Publisher: Apress Publishing>
>>> b.publisher.website
u'http://www.apress.com/'
<Publisher: Apress Publishing>
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12. Foreign Key Value
Publisher
id
name
address
city
state_province
country
website
AutoField
CharField
CharField
CharField
CharField
CharField
URLField
Book
id
title
authors
publisher
AutoField
CharField
ManyToManyField
ForeignKey
>>> p = Publisher.objects.get(name='Apress
Publishing')
>>> p.book_set.all()
[<Book: The Django Book>, <Book: Dive Into
Python>, ...]
>>> p.book_set.filter(name__icontains='django')
[<Book: The Django Book>, <Book: Pro Django>]
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13. Foreign Key Value
Publisher
id
name
address
city
state_province
country
website
AutoField
CharField
CharField
CharField
CharField
CharField
URLField
Book
id
title
authors
publisher
AutoField
CharField
ManyToManyField
ForeignKey
>>> p = Publisher.objects.get(name='Apress
Publishing')
>>> p.book_set.all()
[<Book: The Django Book>, <Book: Dive Into
Python>, ...]
>>> p.book_set.filter(name__icontains='django')
[<Book: The Django Book>, <Book: Pro Django>]
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14. class Book(models.Model):
title = models.CharField(max_length=100)
authors = models.ManyToManyField(Author)
publisher = models.ForeignKey(Publisher)
publication_date = models.DateField()
def __unicode__(self):
return self.title
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15. class Book(models.Model):
title = models.CharField(max_length=100)
authors = models.ManyToManyField(Author)
publisher = models.ForeignKey(Publisher)
publication_date = models.DateField()
def __unicode__(self):
return self.title
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16. Many-to-Many Values
Author
id
first_name
last_name
email
AutoField
CharField
CharField
EmailField
Book
id
title
authors
publisher
AutoField
CharField
ManyToManyField
ForeignKey
>>> b = Book.objects.get(id=50)
>>> b.authors.all()
[<Author: Adrian Holovaty>, <Author:
Jacob Kaplan-Moss>]
>>> b.authors.filter
(first_name='Adrian')
[<Author: Adrian Holovaty>]
>>> b.authors.filter
(first_name='Adam')
[]
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17. Many-to-Many Values
Author
id
first_name
last_name
email
AutoField
CharField
CharField
EmailField
Book
id
title
authors
publisher
AutoField
CharField
ManyToManyField
ForeignKey
>>> a = Author.objects.get(first_name='Adrian',
last_name='Holovaty')
>>> a.book_set.all()
[<Book: The Django Book>, <Book: Adrian's Other
Book>]'
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18. Many-to-Many Values
Author
id
first_name
last_name
email
AutoField
CharField
CharField
EmailField
Book
id
title
authors
publisher
AutoField
CharField
ManyToManyField
ForeignKey
>>> a = Author.objects.get(first_name='Adrian',
last_name='Holovaty')
>>> a.book_set.all()
[<Book: The Django Book>, <Book: Adrian's Other
Book>]'
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19. Update database
schema
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20. First of all
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21. Does not care extra DB table columns
Does not care extra DB tables
Complains if model contains fields that
has not yet been created in the DB table
Django
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22. `syncdb` only create
tables for models which
have not yet been
installed.
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23. Add model fields
Remove model fields
Remove models
Update database schema
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24. Add model fields
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25. Add model fields
Add fields to the model
Check the column definitions for new fields
Add new columns to the DB table
Verify new fields was added properly
In development environments ...
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26. Add model fields
Add fields to the model
Check the column definitions for new fields
Add new columns to the DB table
Verify new fields was added properly
In development environments ...
class Book(models.Model):
title = models.CharField(max_length=100)
authors = models.ManyToManyField(Author)
publisher = models.ForeignKey(Publisher)
publication_date = models.DateField()
num_pages = models.IntegerField(blank=True, null=True)
def __unicode__(self):
return self.title
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27. Add model fields
Add fields to the model
Check the column definitions for new fields
Add new columns to the DB table
Verify new fields was added properly
In development environments ...
CREATE TABLE "books_book" (
"id" serial NOT NULL PRIMARY KEY,
"title" varchar(100) NOT NULL,
"publisher_id" integer NOT NULL REFERENCES "books_publisher" ("id"),
"publication_date" date NOT NULL,
"num_pages" integer NULL
);
$ python manage.py sqlall books
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28. Add model fields
Add fields to the model
Check the column definitions for new fields
Add new columns to the DB table
Verify new fields was added properly
In development environments ...
ALTER TABLE books_book ADD COLUMN num_pages integer;
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29. Add model fields
Add fields to the model
Check the column definitions for new fields
Add new columns to the DB table
Verify new fields was added properly
In development environments ...
>>> from mysite.books.models import Book
>>> Book.objects.all()[:5]
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30. Add model fields
Add new columns to the DB table
Add fields to the model
Restart the web server
In production environments ...
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31. Remove model fields
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32. Add model fields
Remove fields from the model
Restart the web server
Remove columns from the DB table
Remove Normal fields ...
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33. Add model fields
Remove fields from the model
Restart the web server
Remove columns from the DB table
Remove Normal fields ...
ALTER TABLE books_book DROP COLUMN num_pages;
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34. Add model fields
Remove Many-to-Many fields from the model
Restart the web server
Remove Many-to-Many table from the DB
Remove Many-to-Many fields ...
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35. Add model fields
Remove Many-to-Many fields from the model
Restart the web server
Remove Many-to-Many table from the DB
Remove Many-to-Many fields ...
DROP TABLE books_book_authors;
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36. Remove models
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37. Remove model from the models.py
Restart the web server
Remove dependent tables from the DB
Remove the target table from the DB
Remove models
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38. Remove model from the `models.py`
Restart the web server
Remove dependent tables from the DB
Remove the target table from the DB
Remove models
DROP TABLE books_book;
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39. Model methods
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40. class Person(models.Model):
first_name = models.CharField(max_length=50)
last_name = models.CharField(max_length=50)
birth_date = models.DateField()
address = models.CharField(max_length=100)
city = models.CharField(max_length=50)
state = USStateField() # Yes, this is U.S.-centric...
def baby_boomer_status(self):
"Returns the person's baby-boomer status."
import datetime
if datetime.date(1945, 8, 1) <= self.birth_date <= datetime.date(1964, 12, 31):
return "Baby boomer"
if self.birth_date < datetime.date(1945, 8, 1):
return "Pre-boomer"
return "Post-boomer"
def is_midwestern(self):
"Returns True if this person is from the Midwest."
return self.state in ('IL', 'WI', 'MI', 'IN', 'OH', 'IA', 'MO')
def _get_full_name(self):
"Returns the person's full name."
return u'%s %s' % (self.first_name, self.last_name)
full_name = property(_get_full_name)
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41. class Person(models.Model):
first_name = models.CharField(max_length=50)
last_name = models.CharField(max_length=50)
birth_date = models.DateField()
address = models.CharField(max_length=100)
city = models.CharField(max_length=50)
state = USStateField() # Yes, this is U.S.-centric...
def baby_boomer_status(self):
"Returns the person's baby-boomer status."
import datetime
if datetime.date(1945, 8, 1) <= self.birth_date <= datetime.date(1964, 12, 31):
return "Baby boomer"
if self.birth_date < datetime.date(1945, 8, 1):
return "Pre-boomer"
return "Post-boomer"
def is_midwestern(self):
"Returns True if this person is from the Midwest."
return self.state in ('IL', 'WI', 'MI', 'IN', 'OH', 'IA', 'MO')
def _get_full_name(self):
"Returns the person's full name."
return u'%s %s' % (self.first_name, self.last_name)
full_name = property(_get_full_name)
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42. Model methods
>>> p = Person.objects.get(first_name='Barack', last_name='Obama')
>>> p.birth_date
datetime.date(1961, 8, 4)
>>> p.baby_boomer_status()
'Baby boomer'
>>> p.is_midwestern()
True
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43. class Person(models.Model):
first_name = models.CharField(max_length=50)
last_name = models.CharField(max_length=50)
birth_date = models.DateField()
address = models.CharField(max_length=100)
city = models.CharField(max_length=50)
state = USStateField() # Yes, this is U.S.-centric...
def baby_boomer_status(self):
"Returns the person's baby-boomer status."
import datetime
if datetime.date(1945, 8, 1) <= self.birth_date <= datetime.date(1964, 12, 31):
return "Baby boomer"
if self.birth_date < datetime.date(1945, 8, 1):
return "Pre-boomer"
return "Post-boomer"
def is_midwestern(self):
"Returns True if this person is from the Midwest."
return self.state in ('IL', 'WI', 'MI', 'IN', 'OH', 'IA', 'MO')
def _get_full_name(self):
"Returns the person's full name."
return u'%s %s' % (self.first_name, self.last_name)
full_name = property(_get_full_name)
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44. Property methods
>>> p = Person.objects.get(first_name='Barack', last_name='Obama')
>>> p.full_name # Note this isn't a method
u'Barack Obama'
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45. Managers
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46. What is Manager?
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47. Manager
Book.objects.all()
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48. Manager
Book.objects.all()
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49. Manager
“ The interface through which database
query operations are provided to
Django models. ”
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50. Why do we need a
custom Manager?
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51. Add extra Manager methods
Modify initial Manager QuerySets
Custom Mangers
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52. Add extra Manager
methods
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53. Add extra Manager methods
# Get the number of books that have a title ‘Django’
>>> Book.objects.filter(title__icontains='Django')
# Get the number of books that have a title ‘Python’
>>> Book.objects.filter(title__icontains='Python')
# Get the number of books that have a title ‘xxx’
....
# Get the number of books that have a title ‘yyy’
....
.....
.......
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54. Add extra Manager methods
# takes a keyword and returns the number of books
>>> Book.objects.title_count('django')
>>> Book.objects.title_count('python')
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55. # models.py
from django.db import models
# ... Author and Publisher models here ...
class BookManager(models.Manager):
def title_count(self, keyword):
return self.filter(title__icontains=keyword).count()
class Book(models.Model):
title = models.CharField(max_length=100)
authors = models.ManyToManyField(Author)
publisher = models.ForeignKey(Publisher)
publication_date = models.DateField()
num_pages = models.IntegerField(blank=True, null=True)
objects = BookManager()
def __unicode__(self):
return self.title
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56. # models.py
from django.db import models
# ... Author and Publisher models here ...
class BookManager(models.Manager):
def title_count(self, keyword):
return self.filter(title__icontains=keyword).count()
class Book(models.Model):
title = models.CharField(max_length=100)
authors = models.ManyToManyField(Author)
publisher = models.ForeignKey(Publisher)
publication_date = models.DateField()
num_pages = models.IntegerField(blank=True, null=True)
objects = BookManager()
def __unicode__(self):
return self.title
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57. Modify initial Manager
QuerySets
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58. Modify initial Manager QuerySets
Default Manager return all the records
Override Manager’s base QuerySets
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59. Modify initial Manager QuerySets
Default Manager return all the records
Override Manager’s base QuerySets
# returns all books in the book database
>>> Book.objects.all()
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60. Modify initial Manager QuerySets
Default Manager return all the records
Override Manager’s base QuerySets
By overriding the Manager.get_query_set()
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61. Modify initial Manager QuerySets
from django.db import models
# First, define the Manager subclass.
class DahlBookManager(models.Manager):
def get_query_set(self):
return super(DahlBookManager, self).get_query_set()
.filter(author='Roald Dahl')
# Then hook it into the Book model explicitly.
class Book(models.Model):
title = models.CharField(max_length=100)
author = models.CharField(max_length=50)
# ...
objects = models.Manager() # The default manager.
dahl_objects = DahlBookManager() # The Dahl-specific manager.
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62. Modify initial Manager QuerySets
from django.db import models
# First, define the Manager subclass.
class DahlBookManager(models.Manager):
def get_query_set(self):
return super(DahlBookManager, self).get_query_set()
.filter(author='Roald Dahl')
# Then hook it into the Book model explicitly.
class Book(models.Model):
title = models.CharField(max_length=100)
author = models.CharField(max_length=50)
# ...
objects = models.Manager() # The default manager.
dahl_objects = DahlBookManager() # The Dahl-specific manager.
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63. Modify initial Manager QuerySets
>>> Book.dahl_objects.all()
>>> Book.dahl_objects.filter(title='Matilda')
>>> Book.dahl_objects.count()
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64. Another example
class MaleManager(models.Manager):
def get_query_set(self):
return super(MaleManager, self).get_query_set().filter(sex='M')
class FemaleManager(models.Manager):
def get_query_set(self):
return super(FemaleManager, self).get_query_set().filter(sex='F')
class Person(models.Model):
first_name = models.CharField(max_length=50)
last_name = models.CharField(max_length=50)
sex = models.CharField(max_length=1, choices=(('M', 'Male'), ('F', 'Female')))
people = models.Manager()
men = MaleManager()
women = FemaleManager()
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65. Another example
class MaleManager(models.Manager):
def get_query_set(self):
return super(MaleManager, self).get_query_set().filter(sex='M')
class FemaleManager(models.Manager):
def get_query_set(self):
return super(FemaleManager, self).get_query_set().filter(sex='F')
class Person(models.Model):
first_name = models.CharField(max_length=50)
last_name = models.CharField(max_length=50)
sex = models.CharField(max_length=1, choices=(('M', 'Male'), ('F', 'Female')))
people = models.Manager()
men = MaleManager()
women = FemaleManager()
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66. Modify initial Manager QuerySets
>>> Person.men.all()
>>> Person.women.all()
>>> Person.people.all()
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67. Execute raw SQL
queries
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68. Django DB objects
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69. connection object
cursor object
cursor.execute()
cursor.fetchone() / cursor.fetchall()
Implement the Python DB-API (PEP-0249)
Django DB objects
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70. Execute raw SQL queries
>>> from django.db import connection
>>> cursor = connection.cursor()
>>> cursor.execute("""
... SELECT DISTINCT first_name
... FROM people_person
... WHERE last_name = %s""", ['Lennon'])
>>> row = cursor.fetchone()
>>> print row
['John']
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71. Execute raw SQL queries
class PersonManager(models.Manager):
def first_names(self, last_name):
cursor = connection.cursor()
cursor.execute("""
SELECT DISTINCT first_name
FROM people_person
WHERE last_name = %s""", [last_name])
return [row[0] for row in cursor.fetchone()]
class Person(models.Model):
first_name = models.CharField(max_length=50)
last_name = models.CharField(max_length=50)
objects = PersonManager()
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72. Execute raw SQL queries
class PersonManager(models.Manager):
def first_names(self, last_name):
cursor = connection.cursor()
cursor.execute("""
SELECT DISTINCT first_name
FROM people_person
WHERE last_name = %s""", [last_name])
return [row[0] for row in cursor.fetchone()]
class Person(models.Model):
first_name = models.CharField(max_length=50)
last_name = models.CharField(max_length=50)
objects = PersonManager()
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73. Execute raw SQL queries
class PersonManager(models.Manager):
def first_names(self, last_name):
cursor = connection.cursor()
cursor.execute("""
SELECT DISTINCT first_name
FROM people_person
WHERE last_name = %s""", [last_name])
return [row[0] for row in cursor.fetchone()]
class Person(models.Model):
first_name = models.CharField(max_length=50)
last_name = models.CharField(max_length=50)
objects = PersonManager()
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74. Execute raw SQL queries
>>> Person.objects.first_names('Lennon')
['John', 'Cynthia']
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75. More about
Managers
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76. As mentioned previously...
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77. Business logic encapsulation
Add custom Managers
Override default Manager with custom
methods
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78. Add custom Managers
class IncompleteTodoManager(models.Manager):
def get_query_set(self):
return super(TodoManager, self).get_query_set().filter(is_done=False)
class HighPriorityTodoManager(models.Manager):
def get_query_set(self):
return super(TodoManager, self).get_query_set().filter(priority=1)
class Todo(models.Model):
content = models.CharField(max_length=100)
# other fields go here..
objects = models.Manager() # the default manager
# attach our custom managers:
incomplete = models.IncompleteTodoManager()
high_priority = models.HighPriorityTodoManager()
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79. Add custom Managers
class IncompleteTodoManager(models.Manager):
def get_query_set(self):
return super(TodoManager, self).get_query_set().filter(is_done=False)
class HighPriorityTodoManager(models.Manager):
def get_query_set(self):
return super(TodoManager, self).get_query_set().filter(priority=1)
class Todo(models.Model):
content = models.CharField(max_length=100)
# other fields go here..
objects = models.Manager() # the default manager
# attach our custom managers:
incomplete = models.IncompleteTodoManager()
high_priority = models.HighPriorityTodoManager()
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80. Add custom Managers
>>> Todo.incomplete.all()
>>> Todo.high_priority.all()
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81. But
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82. Drawbacks
Verbose Managers
Cluttered model namespace
Not chainable
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83. Custom Manager methods
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84. Custom Manager methods
class TodoManager(models.Manager):
def incomplete(self):
return self.filter(is_done=False)
def high_priority(self):
return self.filter(priority=1)
class Todo(models.Model):
content = models.CharField(max_length=100)
# other fields go here..
objects = TodoManager()
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85. Custom Manager methods
>>> Todo.objects.incomplete()
>>> Todo.objects.high_priority()
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86. But
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87. Drawbacks
Not chainable between custom methods.
# It didn’t work !
>>> Todo.objects.incomplete().high_priority()
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88. Custom QuerySets
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89. Custom QuerySets
class TodoQuerySet(models.query.QuerySet):
def incomplete(self):
return self.filter(is_done=False)
def high_priority(self):
return self.filter(priority=1)
class TodoManager(models.Manager):
def get_query_set(self):
return TodoQuerySet(self.model, using=self._db)
class Todo(models.Model):
content = models.CharField(max_length=100)
# other fields go here..
objects = TodoManager()
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90. Custom QuerySets
class TodoQuerySet(models.query.QuerySet):
def incomplete(self):
return self.filter(is_done=False)
def high_priority(self):
return self.filter(priority=1)
class TodoManager(models.Manager):
def get_query_set(self):
return TodoQuerySet(self.model, using=self._db)
class Todo(models.Model):
content = models.CharField(max_length=100)
# other fields go here..
objects = TodoManager()
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91. Custom QuerySets
>>> Todo.objects.get_query_set().incomplete()
>>> Todo.objects.get_query_set().high_priority()
>>> # (or)
>>> Todo.objects.all().incomplete()
>>> Todo.objects.all().high_priority()
>>> # Chainable !!!
>>> Todo.objects.all().incomplete().high_priority()
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92. But
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93. Custom QuerySets
>>> Todo.objects.get_query_set().incomplete()
>>> Todo.objects.get_query_set().high_priority()
>>> # (or)
>>> Todo.objects.all().incomplete()
>>> Todo.objects.all().high_priority()
>>> # Chainable !!!
>>> Todo.objects.all().incomplete().high_priority()
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94. Custom QuerySets
>>> Todo.objects.get_query_set().incomplete()
>>> Todo.objects.get_query_set().high_priority()
>>> # (or)
>>> Todo.objects.all().incomplete()
>>> Todo.objects.all().high_priority()
>>> # Chainable !!!
>>> Todo.objects.all().incomplete().high_priority()
Ug==Ugly !!
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95. Proxy everything !!
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96. Proxy everything !!
class TodoQuerySet(models.query.QuerySet):
def incomplete(self):
return self.filter(is_done=False)
def high_priority(self):
return self.filter(priority=1)
class TodoManager(models.Manager):
def get_query_set(self):
return TodoQuerySet(self.model, using=self._db)
def incomplete(self):
return self.get_query_set().incomplete()
def high_priority(self):
return self.get_query_set().high_priority()
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97. Proxy everything !!
class TodoQuerySet(models.query.QuerySet):
def incomplete(self):
return self.filter(is_done=False)
def high_priority(self):
return self.filter(priority=1)
class TodoManager(models.Manager):
def get_query_set(self):
return TodoQuerySet(self.model, using=self._db)
def incomplete(self):
return self.get_query_set().incomplete()
def high_priority(self):
return self.get_query_set().high_priority()
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98. Proxy everything !!
>>> Todo.objects.incomplete().high_priority() # Perfect !!
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99. Thank you
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