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"""
Module for abstract serializer/unserializer base classes.
"""
try:
from cStringIO import StringIO
except ImportError:
from StringIO import StringIO
from django.db import models
class SerializationError(Exception):
"""Something bad happened during serialization."""
pass
class DeserializationError(Exception):
"""Something bad happened during deserialization."""
pass
class Serializer(object):
"""
Abstract serializer base class.
"""
def serialize(self, queryset, **options):
"""
Serialize a queryset.
"""
self.options = options
self.stream = options.get("stream", StringIO())
self.selected_fields = options.get("fields")
self.start_serialization()
for obj in queryset:
self.start_object(obj)
for field in obj._meta.fields:
if field.serialize:
if field.rel is None:
if self.selected_fields is None or field.attname in self.selected_fields:
self.handle_field(obj, field)
else:
if self.selected_fields is None or field.attname[:-3] in self.selected_fields:
self.handle_fk_field(obj, field)
for field in obj._meta.many_to_many:
if field.serialize:
if self.selected_fields is None or field.attname in self.selected_fields:
self.handle_m2m_field(obj, field)
self.end_object(obj)
self.end_serialization()
return self.getvalue()
def get_string_value(self, obj, field):
"""
Convert a field's value to a string.
"""
if isinstance(field, models.DateTimeField):
value = getattr(obj, field.name).strftime("%Y-%m-%d %H:%M:%S")
elif isinstance(field, models.FileField):
value = getattr(obj, "get_%s_url" % field.name, lambda: None)()
else:
value = field.flatten_data(follow=None, obj=obj).get(field.name, "")
return str(value)
def start_serialization(self):
"""
Called when serializing of the queryset starts.
"""
raise NotImplementedError
def end_serialization(self):
"""
Called when serializing of the queryset ends.
"""
pass
def start_object(self, obj):
"""
Called when serializing of an object starts.
"""
raise NotImplementedError
def end_object(self, obj):
"""
Called when serializing of an object ends.
"""
pass
def handle_field(self, obj, field):
"""
Called to handle each individual (non-relational) field on an object.
"""
raise NotImplementedError
def handle_fk_field(self, obj, field):
"""
Called to handle a ForeignKey field.
"""
raise NotImplementedError
def handle_m2m_field(self, obj, field):
"""
Called to handle a ManyToManyField.
"""
raise NotImplementedError
def getvalue(self):
"""
Return the fully serialized queryset.
"""
return self.stream.getvalue()
class Deserializer(object):
"""
Abstract base deserializer class.
"""
def __init__(self, stream_or_string, **options):
"""
Init this serializer given a stream or a string
"""
self.options = options
if isinstance(stream_or_string, basestring):
self.stream = StringIO(stream_or_string)
else:
self.stream = stream_or_string
# hack to make sure that the models have all been loaded before
# deserialization starts (otherwise subclass calls to get_model()
# and friends might fail...)
models.get_apps()
def __iter__(self):
return self
def next(self):
"""Iteration iterface -- return the next item in the stream"""
raise NotImplementedError
class DeserializedObject(object):
"""
A deserialized model.
Basically a container for holding the pre-saved deserialized data along
with the many-to-many data saved with the object.
Call ``save()`` to save the object (with the many-to-many data) to the
database; call ``save(save_m2m=False)`` to save just the object fields
(and not touch the many-to-many stuff.)
"""
def __init__(self, obj, m2m_data=None):
self.object = obj
self.m2m_data = m2m_data
def __repr__(self):
return "<DeserializedObject: %s>" % str(self.object)
def save(self, save_m2m=True):
self.object.save()
if self.m2m_data and save_m2m:
for accessor_name, object_list in self.m2m_data.items():
setattr(self.object, accessor_name, object_list)
# prevent a second (possibly accidental) call to save() from saving
# the m2m data twice.
self.m2m_data = None
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