1 """

     2 41. Serialization

     3 

     4 ``django.core.serializers`` provides interfaces to converting Django querysets

     5 to and from "flat" data (i.e. strings).

     6 """

     7 

     8 from django.db import models

     9 

    10 class Category(models.Model):

    11     name = models.CharField(maxlength=20)

    12 

    13     class Meta:

    14        ordering = ('name',)

    15 

    16     def __str__(self):

    17         return self.name

    18 

    19 class Author(models.Model):

    20     name = models.CharField(maxlength=20)

    21 

    22     class Meta:

    23         ordering = ('name',)

    24     

    25     def __str__(self):

    26         return self.name

    27 

    28 class Article(models.Model):

    29     author = models.ForeignKey(Author)

    30     headline = models.CharField(maxlength=50)

    31     pub_date = models.DateTimeField()

    32     categories = models.ManyToManyField(Category)

    33 

    34     class Meta:

    35        ordering = ('pub_date',)

    36 

    37     def __str__(self):

    38         return self.headline

    39 

    40 class AuthorProfile(models.Model):

    41     author = models.OneToOneField(Author)

    42     date_of_birth = models.DateField()

    43     

    44     def __str__(self):

    45         return "Profile of %s" % self.author

    46 

    47 __test__ = {'API_TESTS':"""

    48 # Create some data:

    49 >>> from datetime import datetime

    50 >>> sports = Category(name="Sports")

    51 >>> music = Category(name="Music")

    52 >>> op_ed = Category(name="Op-Ed")

    53 >>> sports.save(); music.save(); op_ed.save()

    54 

    55 >>> joe = Author(name="Joe")

    56 >>> jane = Author(name="Jane")

    57 >>> joe.save(); jane.save()

    58 

    59 >>> a1 = Article(

    60 ...     author = jane,

    61 ...     headline = "Poker has no place on ESPN",

    62 ...     pub_date = datetime(2006, 6, 16, 11, 00))

    63 >>> a2 = Article(

    64 ...     author = joe,

    65 ...     headline = "Time to reform copyright",

    66 ...     pub_date = datetime(2006, 6, 16, 13, 00))

    67 >>> a1.save(); a2.save()

    68 >>> a1.categories = [sports, op_ed]

    69 >>> a2.categories = [music, op_ed]

    70 

    71 # Serialize a queryset to XML

    72 >>> from django.core import serializers

    73 >>> xml = serializers.serialize("xml", Article.objects.all())

    74 

    75 # The output is valid XML

    76 >>> from xml.dom import minidom

    77 >>> dom = minidom.parseString(xml)

    78 

    79 # Deserializing has a similar interface, except that special DeserializedObject

    80 # instances are returned.  This is because data might have changed in the 

    81 # database since the data was serialized (we'll simulate that below).

    82 >>> for obj in serializers.deserialize("xml", xml):

    83 ...     print obj

    84 <DeserializedObject: Poker has no place on ESPN>

    85 <DeserializedObject: Time to reform copyright>

    86 

    87 # Deserializing data with different field values doesn't change anything in the

    88 # database until we call save():

    89 >>> xml = xml.replace("Poker has no place on ESPN", "Poker has no place on television")

    90 >>> objs = list(serializers.deserialize("xml", xml))

    91 

    92 # Even those I deserialized, the database hasn't been touched

    93 >>> Article.objects.all()

    94 [<Article: Poker has no place on ESPN>, <Article: Time to reform copyright>]

    95 

    96 # But when I save, the data changes as you might except.

    97 >>> objs[0].save()

    98 >>> Article.objects.all()

    99 [<Article: Poker has no place on television>, <Article: Time to reform copyright>]

   100 

   101 # Django also ships with a built-in JSON serializers

   102 >>> json = serializers.serialize("json", Category.objects.filter(pk=2))

   103 >>> json

   104 '[{"pk": "2", "model": "serializers.category", "fields": {"name": "Music"}}]'

   105 

   106 # You can easily create new objects by deserializing data with an empty PK

   107 # (It's easier to demo this with JSON...)

   108 >>> new_author_json = '[{"pk": null, "model": "serializers.author", "fields": {"name": "Bill"}}]'

   109 >>> for obj in serializers.deserialize("json", new_author_json):

   110 ...     obj.save()

   111 >>> Author.objects.all()

   112 [<Author: Bill>, <Author: Jane>, <Author: Joe>]

   113 

   114 # All the serializers work the same

   115 >>> json = serializers.serialize("json", Article.objects.all())

   116 >>> for obj in serializers.deserialize("json", json):

   117 ...     print obj

   118 <DeserializedObject: Poker has no place on television>

   119 <DeserializedObject: Time to reform copyright>

   120 

   121 >>> json = json.replace("Poker has no place on television", "Just kidding; I love TV poker")

   122 >>> for obj in serializers.deserialize("json", json):

   123 ...     obj.save()

   124 

   125 >>> Article.objects.all()

   126 [<Article: Just kidding; I love TV poker>, <Article: Time to reform copyright>]

   127 

   128 # If you use your own primary key field (such as a OneToOneField), 

   129 # it doesn't appear in the serialized field list - it replaces the

   130 # pk identifier.

   131 >>> profile = AuthorProfile(author=joe, date_of_birth=datetime(1970,1,1))

   132 >>> profile.save()

   133 

   134 >>> json = serializers.serialize("json", AuthorProfile.objects.all())

   135 >>> json

   136 '[{"pk": "1", "model": "serializers.authorprofile", "fields": {"date_of_birth": "1970-01-01"}}]'

   137 

   138 >>> for obj in serializers.deserialize("json", json):

   139 ...     print obj

   140 <DeserializedObject: Profile of Joe>

   141 

   142 # Objects ids can be referenced before they are defined in the serialization data

   143 # However, the deserialization process will need to be contained within a transaction

   144 >>> 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"}}]'

   145 >>> from django.db import transaction

   146 >>> transaction.enter_transaction_management()

   147 >>> transaction.managed(True)

   148 >>> for obj in serializers.deserialize("json", json):

   149 ...     obj.save()

   150 

   151 >>> transaction.commit()

   152 >>> transaction.leave_transaction_management()

   153 

   154 >>> article = Article.objects.get(pk=3)

   155 >>> article

   156 <Article: Forward references pose no problem>

   157 >>> article.categories.all()

   158 [<Category: Reference>, <Category: Sports>]

   159 >>> article.author

   160 <Author: Agnes>

   161 

   162 """}