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