334 lines
11 KiB
Python
334 lines
11 KiB
Python
# -*- coding: utf-8 -*-
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"""
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42. Serialization
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``django.core.serializers`` provides interfaces to converting Django
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``QuerySet`` objects to and from "flat" data (i.e. strings).
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"""
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try:
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from decimal import Decimal
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except ImportError:
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from django.utils._decimal import Decimal # Python 2.3 fallback
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from django.db import models
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class Category(models.Model):
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name = models.CharField(max_length=20)
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class Meta:
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ordering = ('name',)
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def __unicode__(self):
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return self.name
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class Author(models.Model):
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name = models.CharField(max_length=20)
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class Meta:
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ordering = ('name',)
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def __unicode__(self):
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return self.name
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class Article(models.Model):
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author = models.ForeignKey(Author)
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headline = models.CharField(max_length=50)
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pub_date = models.DateTimeField()
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categories = models.ManyToManyField(Category)
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class Meta:
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ordering = ('pub_date',)
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def __unicode__(self):
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return self.headline
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class AuthorProfile(models.Model):
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author = models.OneToOneField(Author, primary_key=True)
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date_of_birth = models.DateField()
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def __unicode__(self):
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return u"Profile of %s" % self.author
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class Actor(models.Model):
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name = models.CharField(max_length=20, primary_key=True)
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class Meta:
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ordering = ('name',)
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def __unicode__(self):
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return self.name
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class Movie(models.Model):
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actor = models.ForeignKey(Actor)
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title = models.CharField(max_length=50)
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price = models.DecimalField(max_digits=6, decimal_places=2, default=Decimal('0.00'))
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class Meta:
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ordering = ('title',)
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def __unicode__(self):
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return self.title
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class Score(models.Model):
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score = models.FloatField()
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class Team(object):
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def __init__(self, title):
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self.title = title
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def __unicode__(self):
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raise NotImplementedError("Not so simple")
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def __str__(self):
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raise NotImplementedError("Not so simple")
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def to_string(self):
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return "%s" % self.title
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class TeamField(models.CharField):
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__metaclass__ = models.SubfieldBase
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def __init__(self):
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super(TeamField, self).__init__(max_length=100)
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def get_db_prep_save(self, value):
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return unicode(value.title)
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def to_python(self, value):
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if isinstance(value, Team):
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return value
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return Team(value)
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def value_to_string(self, obj):
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return self._get_val_from_obj(obj).to_string()
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class Player(models.Model):
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name = models.CharField(max_length=50)
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rank = models.IntegerField()
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team = TeamField()
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def __unicode__(self):
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return u'%s (%d) playing for %s' % (self.name, self.rank, self.team.to_string())
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__test__ = {'API_TESTS':"""
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# Create some data:
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>>> from datetime import datetime
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>>> sports = Category(name="Sports")
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>>> music = Category(name="Music")
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>>> op_ed = Category(name="Op-Ed")
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>>> sports.save(); music.save(); op_ed.save()
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>>> joe = Author(name="Joe")
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>>> jane = Author(name="Jane")
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>>> joe.save(); jane.save()
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>>> a1 = Article(
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... author = jane,
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... headline = "Poker has no place on ESPN",
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... pub_date = datetime(2006, 6, 16, 11, 00))
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>>> a2 = Article(
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... author = joe,
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... headline = "Time to reform copyright",
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... pub_date = datetime(2006, 6, 16, 13, 00, 11, 345))
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>>> a1.save(); a2.save()
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>>> a1.categories = [sports, op_ed]
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>>> a2.categories = [music, op_ed]
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# Serialize a queryset to XML
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>>> from django.core import serializers
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>>> xml = serializers.serialize("xml", Article.objects.all())
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# The output is valid XML
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>>> from xml.dom import minidom
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>>> dom = minidom.parseString(xml)
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# Deserializing has a similar interface, except that special DeserializedObject
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# instances are returned. This is because data might have changed in the
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# database since the data was serialized (we'll simulate that below).
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>>> for obj in serializers.deserialize("xml", xml):
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... print obj
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<DeserializedObject: Poker has no place on ESPN>
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<DeserializedObject: Time to reform copyright>
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# Deserializing data with different field values doesn't change anything in the
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# database until we call save():
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>>> xml = xml.replace("Poker has no place on ESPN", "Poker has no place on television")
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>>> objs = list(serializers.deserialize("xml", xml))
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# Even those I deserialized, the database hasn't been touched
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>>> Article.objects.all()
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[<Article: Poker has no place on ESPN>, <Article: Time to reform copyright>]
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# But when I save, the data changes as you might except.
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>>> objs[0].save()
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>>> Article.objects.all()
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[<Article: Poker has no place on television>, <Article: Time to reform copyright>]
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# Django also ships with a built-in JSON serializers
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>>> json = serializers.serialize("json", Category.objects.filter(pk=2))
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>>> json
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'[{"pk": 2, "model": "serializers.category", "fields": {"name": "Music"}}]'
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# You can easily create new objects by deserializing data with an empty PK
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# (It's easier to demo this with JSON...)
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>>> new_author_json = '[{"pk": null, "model": "serializers.author", "fields": {"name": "Bill"}}]'
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>>> for obj in serializers.deserialize("json", new_author_json):
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... obj.save()
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>>> Author.objects.all()
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[<Author: Bill>, <Author: Jane>, <Author: Joe>]
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# All the serializers work the same
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>>> json = serializers.serialize("json", Article.objects.all())
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>>> for obj in serializers.deserialize("json", json):
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... print obj
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<DeserializedObject: Poker has no place on television>
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<DeserializedObject: Time to reform copyright>
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>>> json = json.replace("Poker has no place on television", "Just kidding; I love TV poker")
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>>> for obj in serializers.deserialize("json", json):
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... obj.save()
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>>> Article.objects.all()
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[<Article: Just kidding; I love TV poker>, <Article: Time to reform copyright>]
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# If you use your own primary key field (such as a OneToOneField),
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# it doesn't appear in the serialized field list - it replaces the
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# pk identifier.
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>>> profile = AuthorProfile(author=joe, date_of_birth=datetime(1970,1,1))
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>>> profile.save()
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>>> json = serializers.serialize("json", AuthorProfile.objects.all())
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>>> json
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'[{"pk": 1, "model": "serializers.authorprofile", "fields": {"date_of_birth": "1970-01-01"}}]'
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>>> for obj in serializers.deserialize("json", json):
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... print obj
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<DeserializedObject: Profile of Joe>
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# Objects ids can be referenced before they are defined in the serialization data
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# However, the deserialization process will need to be contained within a transaction
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>>> 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"}}]'
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>>> from django.db import transaction
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>>> transaction.enter_transaction_management()
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>>> transaction.managed(True)
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>>> for obj in serializers.deserialize("json", json):
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... obj.save()
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>>> transaction.commit()
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>>> transaction.leave_transaction_management()
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>>> article = Article.objects.get(pk=3)
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>>> article
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<Article: Forward references pose no problem>
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>>> article.categories.all()
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[<Category: Reference>, <Category: Sports>]
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>>> article.author
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<Author: Agnes>
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# Serializer output can be restricted to a subset of fields
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>>> print serializers.serialize("json", Article.objects.all(), fields=('headline','pub_date'))
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[{"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"}}]
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# Every string is serialized as a unicode object, also primary key
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# which is 'varchar'
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>>> ac = Actor(name="Zażółć")
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>>> mv = Movie(title="Gęślą jaźń", actor=ac)
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>>> ac.save(); mv.save()
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# Let's serialize our movie
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>>> print serializers.serialize("json", [mv])
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[{"pk": 1, "model": "serializers.movie", "fields": {"price": "0.00", "actor": "Za\u017c\u00f3\u0142\u0107", "title": "G\u0119\u015bl\u0105 ja\u017a\u0144"}}]
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# Deserialization of movie
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>>> list(serializers.deserialize('json', serializers.serialize('json', [mv])))[0].object.title
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u'G\u0119\u015bl\u0105 ja\u017a\u0144'
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# None is null after serialization to json
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# Primary key is None in case of not saved model
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>>> mv2 = Movie(title="Movie 2", actor=ac)
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>>> print serializers.serialize("json", [mv2])
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[{"pk": null, "model": "serializers.movie", "fields": {"price": "0.00", "actor": "Za\u017c\u00f3\u0142\u0107", "title": "Movie 2"}}]
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# Deserialization of null returns None for pk
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>>> print list(serializers.deserialize('json', serializers.serialize('json', [mv2])))[0].object.id
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None
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# Serialization and deserialization of floats:
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>>> sc = Score(score=3.4)
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>>> print serializers.serialize("json", [sc])
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[{"pk": null, "model": "serializers.score", "fields": {"score": 3.4}}]
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>>> print list(serializers.deserialize('json', serializers.serialize('json', [sc])))[0].object.score
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3.4
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# Custom field with non trivial to string convertion value
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>>> player = Player()
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>>> player.name = "Soslan Djanaev"
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>>> player.rank = 1
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>>> player.team = Team("Spartak Moskva")
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>>> player.save()
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>>> serialized = serializers.serialize("json", Player.objects.all())
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>>> print serialized
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[{"pk": 1, "model": "serializers.player", "fields": {"name": "Soslan Djanaev", "rank": 1, "team": "Spartak Moskva"}}]
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>>> obj = list(serializers.deserialize("json", serialized))[0]
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>>> print obj
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<DeserializedObject: Soslan Djanaev (1) playing for Spartak Moskva>
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"""}
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try:
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import yaml
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__test__['YAML'] = """
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# Create some data:
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>>> articles = Article.objects.all().order_by("id")[:2]
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>>> from django.core import serializers
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# test if serial
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>>> serialized = serializers.serialize("yaml", articles)
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>>> print serialized
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- fields:
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author: 2
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categories: [3, 1]
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headline: Just kidding; I love TV poker
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pub_date: 2006-06-16 11:00:00
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model: serializers.article
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pk: 1
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- fields:
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author: 1
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categories: [2, 3]
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headline: Time to reform copyright
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pub_date: 2006-06-16 13:00:11
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model: serializers.article
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pk: 2
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<BLANKLINE>
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>>> obs = list(serializers.deserialize("yaml", serialized))
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>>> for i in obs:
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... print i
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<DeserializedObject: Just kidding; I love TV poker>
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<DeserializedObject: Time to reform copyright>
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# Custom field with non trivial to string convertion value with YAML serializer
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>>> print serializers.serialize("yaml", Player.objects.all())
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- fields: {name: Soslan Djanaev, rank: 1, team: Spartak Moskva}
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model: serializers.player
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pk: 1
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<BLANKLINE>
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>>> serialized = serializers.serialize("yaml", Player.objects.all())
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>>> obj = list(serializers.deserialize("yaml", serialized))[0]
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>>> print obj
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<DeserializedObject: Soslan Djanaev (1) playing for Spartak Moskva>
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"""
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except ImportError:
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pass
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