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# -*- coding: utf-8 -*-
"""
42. Serialization
``django.core.serializers`` provides interfaces to converting Django
``QuerySet`` objects to and from "flat" data (i.e. strings).
"""
from decimal import Decimal
from django.db import models
class Category(models.Model):
name = models.CharField(max_length=20)
class Meta:
ordering = ('name',)
def __unicode__(self):
return self.name
class Author(models.Model):
name = models.CharField(max_length=20)
class Meta:
ordering = ('name',)
def __unicode__(self):
return self.name
class Article(models.Model):
author = models.ForeignKey(Author)
headline = models.CharField(max_length=50)
pub_date = models.DateTimeField()
categories = models.ManyToManyField(Category)
class Meta:
ordering = ('pub_date',)
def __unicode__(self):
return self.headline
class AuthorProfile(models.Model):
author = models.OneToOneField(Author, primary_key=True)
date_of_birth = models.DateField()
def __unicode__(self):
return u"Profile of %s" % self.author
class Actor(models.Model):
name = models.CharField(max_length=20, primary_key=True)
class Meta:
ordering = ('name',)
def __unicode__(self):
return self.name
class Movie(models.Model):
actor = models.ForeignKey(Actor)
title = models.CharField(max_length=50)
price = models.DecimalField(max_digits=6, decimal_places=2, default=Decimal('0.00'))
class Meta:
ordering = ('title',)
def __unicode__(self):
return self.title
class Score(models.Model):
score = models.FloatField()
class Team(object):
def __init__(self, title):
self.title = title
def __unicode__(self):
raise NotImplementedError("Not so simple")
def __str__(self):
raise NotImplementedError("Not so simple")
def to_string(self):
return "%s" % self.title
class TeamField(models.CharField):
__metaclass__ = models.SubfieldBase
def __init__(self):
super(TeamField, self).__init__(max_length=100)
def get_db_prep_save(self, value):
return unicode(value.title)
def to_python(self, value):
if isinstance(value, Team):
return value
return Team(value)
def value_to_string(self, obj):
return self._get_val_from_obj(obj).to_string()
class Player(models.Model):
name = models.CharField(max_length=50)
rank = models.IntegerField()
team = TeamField()
def __unicode__(self):
return u'%s (%d) playing for %s' % (self.name, self.rank, self.team.to_string())
__test__ = {'API_TESTS':"""
# Create some data:
>>> from datetime import datetime
>>> sports = Category(name="Sports")
>>> music = Category(name="Music")
>>> op_ed = Category(name="Op-Ed")
>>> sports.save(); music.save(); op_ed.save()
>>> joe = Author(name="Joe")
>>> jane = Author(name="Jane")
>>> joe.save(); jane.save()
>>> a1 = Article(
... author = jane,
... headline = "Poker has no place on ESPN",
... pub_date = datetime(2006, 6, 16, 11, 00))
>>> a2 = Article(
... author = joe,
... headline = "Time to reform copyright",
... pub_date = datetime(2006, 6, 16, 13, 00, 11, 345))
>>> a1.save(); a2.save()
>>> a1.categories = [sports, op_ed]
>>> a2.categories = [music, op_ed]
# Serialize a queryset to XML
>>> from django.core import serializers
>>> xml = serializers.serialize("xml", Article.objects.all())
# The output is valid XML
>>> from xml.dom import minidom
>>> dom = minidom.parseString(xml)
# Deserializing has a similar interface, except that special DeserializedObject
# instances are returned. This is because data might have changed in the
# database since the data was serialized (we'll simulate that below).
>>> for obj in serializers.deserialize("xml", xml):
... print obj
<DeserializedObject: serializers.Article(pk=1)>
<DeserializedObject: serializers.Article(pk=2)>
# Deserializing data with different field values doesn't change anything in the
# database until we call save():
>>> xml = xml.replace("Poker has no place on ESPN", "Poker has no place on television")
>>> objs = list(serializers.deserialize("xml", xml))
# Even those I deserialized, the database hasn't been touched
>>> Article.objects.all()
[<Article: Poker has no place on ESPN>, <Article: Time to reform copyright>]
# But when I save, the data changes as you might except.
>>> objs[0].save()
>>> Article.objects.all()
[<Article: Poker has no place on television>, <Article: Time to reform copyright>]
# Django also ships with a built-in JSON serializers
>>> json = serializers.serialize("json", Category.objects.filter(pk=2))
>>> json
'[{"pk": 2, "model": "serializers.category", "fields": {"name": "Music"}}]'
# You can easily create new objects by deserializing data with an empty PK
# (It's easier to demo this with JSON...)
>>> new_author_json = '[{"pk": null, "model": "serializers.author", "fields": {"name": "Bill"}}]'
>>> for obj in serializers.deserialize("json", new_author_json):
... obj.save()
>>> Author.objects.all()
[<Author: Bill>, <Author: Jane>, <Author: Joe>]
# All the serializers work the same
>>> json = serializers.serialize("json", Article.objects.all())
>>> for obj in serializers.deserialize("json", json):
... print obj
<DeserializedObject: serializers.Article(pk=1)>
<DeserializedObject: serializers.Article(pk=2)>
>>> json = json.replace("Poker has no place on television", "Just kidding; I love TV poker")
>>> for obj in serializers.deserialize("json", json):
... obj.save()
>>> Article.objects.all()
[<Article: Just kidding; I love TV poker>, <Article: Time to reform copyright>]
# If you use your own primary key field (such as a OneToOneField),
# it doesn't appear in the serialized field list - it replaces the
# pk identifier.
>>> profile = AuthorProfile(author=joe, date_of_birth=datetime(1970,1,1))
>>> profile.save()
>>> json = serializers.serialize("json", AuthorProfile.objects.all())
>>> json
'[{"pk": 1, "model": "serializers.authorprofile", "fields": {"date_of_birth": "1970-01-01"}}]'
>>> for obj in serializers.deserialize("json", json):
... print obj
<DeserializedObject: serializers.AuthorProfile(pk=1)>
# Objects ids can be referenced before they are defined in the serialization data
# However, the deserialization process will need to be contained within a transaction
>>> json = '[{"pk": 3, "model": "serializers.article", "fields": {"headline": "Forward references pose no problem", "pub_date": "2006-06-16 15:00:00", "categories": [4, 1], "author": 4}}, {"pk": 4, "model": "serializers.category", "fields": {"name": "Reference"}}, {"pk": 4, "model": "serializers.author", "fields": {"name": "Agnes"}}]'
>>> from django.db import transaction
>>> transaction.enter_transaction_management()
>>> transaction.managed(True)
>>> for obj in serializers.deserialize("json", json):
... obj.save()
>>> transaction.commit()
>>> transaction.leave_transaction_management()
>>> article = Article.objects.get(pk=3)
>>> article
<Article: Forward references pose no problem>
>>> article.categories.all()
[<Category: Reference>, <Category: Sports>]
>>> article.author
<Author: Agnes>
# Serializer output can be restricted to a subset of fields
>>> print serializers.serialize("json", Article.objects.all(), fields=('headline','pub_date'))
[{"pk": 1, "model": "serializers.article", "fields": {"headline": "Just kidding; I love TV poker", "pub_date": "2006-06-16 11:00:00"}}, {"pk": 2, "model": "serializers.article", "fields": {"headline": "Time to reform copyright", "pub_date": "2006-06-16 13:00:11"}}, {"pk": 3, "model": "serializers.article", "fields": {"headline": "Forward references pose no problem", "pub_date": "2006-06-16 15:00:00"}}]
# Every string is serialized as a unicode object, also primary key
# which is 'varchar'
>>> ac = Actor(name="Zażółć")
>>> mv = Movie(title="Gęślą jaźń", actor=ac)
>>> ac.save(); mv.save()
# Let's serialize our movie
>>> print serializers.serialize("json", [mv])
[{"pk": 1, "model": "serializers.movie", "fields": {"price": "0.00", "actor": "Za\u017c\u00f3\u0142\u0107", "title": "G\u0119\u015bl\u0105 ja\u017a\u0144"}}]
# Deserialization of movie
>>> list(serializers.deserialize('json', serializers.serialize('json', [mv])))[0].object.title
u'G\u0119\u015bl\u0105 ja\u017a\u0144'
# None is null after serialization to json
# Primary key is None in case of not saved model
>>> mv2 = Movie(title="Movie 2", actor=ac)
>>> print serializers.serialize("json", [mv2])
[{"pk": null, "model": "serializers.movie", "fields": {"price": "0.00", "actor": "Za\u017c\u00f3\u0142\u0107", "title": "Movie 2"}}]
# Deserialization of null returns None for pk
>>> print list(serializers.deserialize('json', serializers.serialize('json', [mv2])))[0].object.id
None
# Serialization and deserialization of floats:
>>> sc = Score(score=3.4)
>>> print serializers.serialize("json", [sc])
[{"pk": null, "model": "serializers.score", "fields": {"score": 3.4}}]
>>> print list(serializers.deserialize('json', serializers.serialize('json', [sc])))[0].object.score
3.4
# Custom field with non trivial to string convertion value
>>> player = Player()
>>> player.name = "Soslan Djanaev"
>>> player.rank = 1
>>> player.team = Team("Spartak Moskva")
>>> player.save()
>>> serialized = serializers.serialize("json", Player.objects.all())
>>> print serialized
[{"pk": 1, "model": "serializers.player", "fields": {"name": "Soslan Djanaev", "rank": 1, "team": "Spartak Moskva"}}]
>>> obj = list(serializers.deserialize("json", serialized))[0]
>>> print obj
<DeserializedObject: serializers.Player(pk=1)>
# Regression for #12524 -- dates before 1000AD get prefixed 0's on the year
>>> a = Article.objects.create(
... pk=4,
... author = jane,
... headline = "Nobody remembers the early years",
... pub_date = datetime(1, 2, 3, 4, 5, 6))
>>> serialized = serializers.serialize("json", [a])
>>> print serialized
[{"pk": 4, "model": "serializers.article", "fields": {"headline": "Nobody remembers the early years", "pub_date": "0001-02-03 04:05:06", "categories": [], "author": 2}}]
>>> obj = list(serializers.deserialize("json", serialized))[0]
>>> print obj.object.pub_date
0001-02-03 04:05:06
"""}
try:
import yaml
__test__['YAML'] = """
# Create some data:
>>> articles = Article.objects.all().order_by("id")[:2]
>>> from django.core import serializers
# test if serial
>>> serialized = serializers.serialize("yaml", articles)
>>> print serialized
- fields:
author: 2
categories: [3, 1]
headline: Just kidding; I love TV poker
pub_date: 2006-06-16 11:00:00
model: serializers.article
pk: 1
- fields:
author: 1
categories: [2, 3]
headline: Time to reform copyright
pub_date: 2006-06-16 13:00:11
model: serializers.article
pk: 2
<BLANKLINE>
>>> obs = list(serializers.deserialize("yaml", serialized))
>>> for i in obs:
... print i
<DeserializedObject: serializers.Article(pk=1)>
<DeserializedObject: serializers.Article(pk=2)>
# Custom field with non trivial to string convertion value with YAML serializer
>>> print serializers.serialize("yaml", Player.objects.all())
- fields: {name: Soslan Djanaev, rank: 1, team: Spartak Moskva}
model: serializers.player
pk: 1
<BLANKLINE>
>>> serialized = serializers.serialize("yaml", Player.objects.all())
>>> obj = list(serializers.deserialize("yaml", serialized))[0]
>>> print obj
<DeserializedObject: serializers.Player(pk=1)>
"""
except ImportError:
pass
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