The django book - Chap10 : Advanced Models

Advanced Models

「The Django Book」 Chapter 10

Spin Lai

July 23, 20132013年7月24日星期三

賴司平 (Spin)

資拓宏宇氣象科技事業處

PHP、Javascript、Python

About me

2013年7月24日星期三

Related objects Update database schema Model methods Managers Execute raw SQL queries More about Managers

Today’s topics

Related objects

Recalling the Chapter 5 ...

Publisheridnameaddresscitystate_provincecountrywebsite

AutoFieldCharFieldCharFieldCharFieldCharFieldCharFieldURLField

Bookidtitleauthorspublisherpublication_date

AutoFieldCharFieldManyToManyFieldForeignKeyDateField

Authoridfirst_namelast_nameemail

AutoFieldCharFieldCharFieldEmailField

N:1N:M

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

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)

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

Foreign Key Value

Bookidtitleauthorspublisher

AutoFieldCharFieldManyToManyFieldForeignKey

>>> b = Book.objects.get(id=50)>>> b.publisher<Publisher: Apress Publishing>>>> b.publisher.websiteu'http://www.apress.com/'<Publisher: Apress Publishing>

Foreign Key Value

>>> 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>]

Foreign Key Value

>>> 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>]

Many-to-Many Values

>>> 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')[]

Many-to-Many Values

>>> a = Author.objects.get(first_name='Adrian', last_name='Holovaty')>>> a.book_set.all()[<Book: The Django Book>, <Book: Adrian's Other Book>]'

Many-to-Many Values

>>> a = Author.objects.get(first_name='Adrian', last_name='Holovaty')>>> a.book_set.all()[<Book: The Django Book>, <Book: Adrian's Other Book>]'

Update database schema

First of all

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

`syncdb` only create tables for models which

have not yet been installed.

Add model fields Remove model fields Remove models

Update database schema

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 ...

Add model fields

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)

Add model fields

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

Add model fields

ALTER TABLE books_book ADD COLUMN num_pages integer;

Add model fields

>>> from mysite.books.models import Book>>> Book.objects.all()[:5]

Add model fields

Add new columns to the DB table Add fields to the model Restart the web server

In production environments ...

Remove model fields

Add model fields

Remove fields from the model Restart the web server Remove columns from the DB table

Remove Normal fields ...

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;

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 ...

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;

Remove models

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

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;

Model methods

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)

Model methods

>>> p = Person.objects.get(first_name='Barack', last_name='Obama')>>> p.birth_datedatetime.date(1961, 8, 4)>>> p.baby_boomer_status()'Baby boomer'>>> p.is_midwestern()True

Property methods

>>> p = Person.objects.get(first_name='Barack', last_name='Obama')>>> p.full_name # Note this isn't a method u'Barack Obama'

Managers

What is Manager?

Manager

Book.objects.all()

Manager

Book.objects.all()

Manager

“ The interface through which database query operations are provided to Django models. ”

Why do we need a custom Manager?

Add extra Manager methods Modify initial Manager QuerySets

Custom Mangers

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’ .... ..... .......

# takes a keyword and returns the number of books>>> Book.objects.title_count('django')

>>> Book.objects.title_count('python')

# models.pyfrom 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()

# models.pyfrom 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()

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()

By overriding the Manager.get_query_set()

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.

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.

>>> Book.dahl_objects.all()>>> Book.dahl_objects.filter(title='Matilda')>>> Book.dahl_objects.count()

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()

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()

>>> Person.men.all()>>> Person.women.all()>>> Person.people.all()

Execute raw SQL queries

Django DB objects

connection object cursor object cursor.execute() cursor.fetchone() / cursor.fetchall() Implement the Python DB-API (PEP-0249)

Django DB objects

>>> 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']

Execute raw SQL queriesclass 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()

>>> Person.objects.first_names('Lennon')['John', 'Cynthia']

More about Managers

As mentioned previously...

Business logic encapsulation

Add custom Managers Override default Manager with custom

methods

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()

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)

objects = models.Manager() # the default manager

# attach our custom managers: incomplete = models.IncompleteTodoManager() high_priority = models.HighPriorityTodoManager()

Add custom Managers

>>> Todo.incomplete.all()>>> Todo.high_priority.all()

Drawbacks

Verbose Managers Cluttered model namespace Not chainable

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)

objects = TodoManager()

>>> Todo.objects.incomplete()>>> Todo.objects.high_priority()

Drawbacks

Not chainable between custom methods.

# It didn’t work !>>> Todo.objects.incomplete().high_priority()

Custom QuerySets

class TodoQuerySet(models.query.QuerySet): def incomplete(self): return self.filter(is_done=False)

class TodoManager(models.Manager): def get_query_set(self): return TodoQuerySet(self.model, using=self._db)

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()

Custom QuerySets

Ug==Ugly !!

Proxy everything !!

def incomplete(self): return self.get_query_set().incomplete()

def high_priority(self): return self.get_query_set().high_priority()

Proxy everything !!

def incomplete(self): return self.get_query_set().incomplete()

def high_priority(self): return self.get_query_set().high_priority()

Proxy everything !!

>>> Todo.objects.incomplete().high_priority() # Perfect !!

Thank you

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