The django book - Chap10 : Advanced Models

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Advanced Models The Django Book Chapter 10 4QJO -BJ +VMZ ϋ˜˚݋ಂɧ

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፠̡̻ 4QJO ༟ן҃ρ ं൥߅Ҧԫุஈ 1)1e+BWBTDSJQUe1ZUIPO About me ϋ˜˚݋ಂɧ

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3FMBUFE PCKFDUT 6QEBUF EBUBCBTF TDIFNB .PEFM NFUIPET .BOBHFST &YFDVUF SBX 42- RVFSJFT .PSF BCPVU .BOBHFST Today’s topics ϋ˜˚݋ಂɧ

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Related objects ϋ˜˚݋ಂɧ

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Recalling the Chapter 5 ... ϋ˜˚݋ಂɧ

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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:1 N:M ϋ˜˚݋ಂɧ

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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 ϋ˜˚݋ಂɧ

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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) ϋ˜˚݋ಂɧ

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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 ϋ˜˚݋ಂɧ

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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 >>> b.publisher.website u'http://www.apress.com/' ϋ˜˚݋ಂɧ

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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() [, , ...] >>> p.book_set.filter(name__icontains='django') [, ] ϋ˜˚݋ಂɧ

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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() [, , ...] >>> p.book_set.filter(name__icontains='django') [, ] ϋ˜˚݋ಂɧ

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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() [, ] >>> b.authors.filter (first_name='Adrian') [] >>> b.authors.filter (first_name='Adam') [] ϋ˜˚݋ಂɧ

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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() [, ]' ϋ˜˚݋ಂɧ

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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() [, ]' ϋ˜˚݋ಂɧ

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Update database schema ϋ˜˚݋ಂɧ

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First of all ϋ˜˚݋ಂɧ

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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 ϋ˜˚݋ಂɧ

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`syncdb` only create tables for models which have not yet been installed. ϋ˜˚݋ಂɧ

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"EE NPEFM GJFMET 3FNPWF NPEFM GJFMET 3FNPWF NPEFMT Update database schema ϋ˜˚݋ಂɧ

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Add model ﬁelds ϋ˜˚݋ಂɧ

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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 ... ϋ˜˚݋ಂɧ

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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 ϋ˜˚݋ಂɧ

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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 ϋ˜˚݋ಂɧ

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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; ϋ˜˚݋ಂɧ

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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] ϋ˜˚݋ಂɧ

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Add model ﬁelds Add new columns to the DB table Add ﬁelds to the model Restart the web server In production environments ... ϋ˜˚݋ಂɧ

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Remove model ﬁelds ϋ˜˚݋ಂɧ

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Add model fields Remove fields from the model Restart the web server Remove columns from the DB table Remove Normal fields ... ϋ˜˚݋ಂɧ

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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; ϋ˜˚݋ಂɧ

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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 ... ϋ˜˚݋ಂɧ

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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; ϋ˜˚݋ಂɧ

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Remove models ϋ˜˚݋ಂɧ

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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 ϋ˜˚݋ಂɧ

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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; ϋ˜˚݋ಂɧ

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Model methods ϋ˜˚݋ಂɧ

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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) ϋ˜˚݋ಂɧ

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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 ϋ˜˚݋ಂɧ

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Property methods >>> p = Person.objects.get(first_name='Barack', last_name='Obama') >>> p.full_name # Note this isn't a method u'Barack Obama' ϋ˜˚݋ಂɧ

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Managers ϋ˜˚݋ಂɧ

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What is Manager? ϋ˜˚݋ಂɧ

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Manager Book.objects.all() ϋ˜˚݋ಂɧ

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Manager Book.objects.all() ϋ˜˚݋ಂɧ

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Manager “ The interface through which database query operations are provided to Django models. ” ϋ˜˚݋ಂɧ

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Why do we need a custom Manager? ϋ˜˚݋ಂɧ

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"EE FYUSB .BOBHFS NFUIPET .PEJGZ JOJUJBM .BOBHFS 2VFSZ4FUT Custom Mangers ϋ˜˚݋ಂɧ

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Add extra Manager methods ϋ˜˚݋ಂɧ

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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’ .... ..... ....... ϋ˜˚݋ಂɧ

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Add extra Manager methods # takes a keyword and returns the number of books >>> Book.objects.title_count('django') >>> Book.objects.title_count('python') ϋ˜˚݋ಂɧ

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# 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 ϋ˜˚݋ಂɧ

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Modify initial Manager QuerySets ϋ˜˚݋ಂɧ

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Modify initial Manager QuerySets Default Manager return all the records Override Manager’s base QuerySets ϋ˜˚݋ಂɧ

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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() ϋ˜˚݋ಂɧ

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Modify initial Manager QuerySets Default Manager return all the records Override Manager’s base QuerySets By overriding the Manager.get_query_set() ϋ˜˚݋ಂɧ

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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. ϋ˜˚݋ಂɧ

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Modify initial Manager QuerySets >>> Book.dahl_objects.all() >>> Book.dahl_objects.filter(title='Matilda') >>> Book.dahl_objects.count() ϋ˜˚݋ಂɧ

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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() ϋ˜˚݋ಂɧ

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Modify initial Manager QuerySets >>> Person.men.all() >>> Person.women.all() >>> Person.people.all() ϋ˜˚݋ಂɧ

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Execute raw SQL queries ϋ˜˚݋ಂɧ

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Django DB objects ϋ˜˚݋ಂɧ

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connection object cursor object cursor.execute() cursor.fetchone() / cursor.fetchall() Implement the Python DB-API (PEP-0249) Django DB objects ϋ˜˚݋ಂɧ

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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'] ϋ˜˚݋ಂɧ

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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() ϋ˜˚݋ಂɧ

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Execute raw SQL queries >>> Person.objects.first_names('Lennon') ['John', 'Cynthia'] ϋ˜˚݋ಂɧ

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More about Managers ϋ˜˚݋ಂɧ

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As mentioned previously... ϋ˜˚݋ಂɧ

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Business logic encapsulation Add custom Managers Override default Manager with custom methods ϋ˜˚݋ಂɧ

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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() ϋ˜˚݋ಂɧ

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Add custom Managers >>> Todo.incomplete.all() >>> Todo.high_priority.all() ϋ˜˚݋ಂɧ

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But ϋ˜˚݋ಂɧ

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Drawbacks Verbose Managers Cluttered model namespace Not chainable ϋ˜˚݋ಂɧ

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Custom Manager methods ϋ˜˚݋ಂɧ

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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() ϋ˜˚݋ಂɧ

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Custom Manager methods >>> Todo.objects.incomplete() >>> Todo.objects.high_priority() ϋ˜˚݋ಂɧ

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But ϋ˜˚݋ಂɧ

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Drawbacks Not chainable between custom methods. # It didn’t work ! >>> Todo.objects.incomplete().high_priority() ϋ˜˚݋ಂɧ

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Custom QuerySets ϋ˜˚݋ಂɧ

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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() ϋ˜˚݋ಂɧ

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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() ϋ˜˚݋ಂɧ

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But ϋ˜˚݋ಂɧ

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Proxy everything !! ϋ˜˚݋ಂɧ

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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() ϋ˜˚݋ಂɧ

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Proxy everything !! >>> Todo.objects.incomplete().high_priority() # Perfect !! ϋ˜˚݋ಂɧ

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Thank you ϋ˜˚݋ಂɧ