""" Module for abstract serializer/unserializer base classes. """ from io import StringIO from django.db import models class SerializerDoesNotExist(KeyError): """The requested serializer was not found.""" pass class SerializationError(Exception): """Something bad happened during serialization.""" pass class DeserializationError(Exception): """Something bad happened during deserialization.""" @classmethod def WithData(cls, original_exc, model, fk, field_value): """ Factory method for creating a deserialization error which has a more explanatory message. """ return cls("%s: (%s:pk=%s) field_value was '%s'" % (original_exc, model, fk, field_value)) class ProgressBar(object): progress_width = 75 def __init__(self, output, total_count): self.output = output self.total_count = total_count self.prev_done = 0 def update(self, count): if not self.output: return perc = count * 100 // self.total_count done = perc * self.progress_width // 100 if self.prev_done >= done: return self.prev_done = done cr = '' if self.total_count == 1 else '\r' self.output.write(cr + '[' + '.' * done + ' ' * (self.progress_width - done) + ']') if done == self.progress_width: self.output.write('\n') self.output.flush() class Serializer(object): """ Abstract serializer base class. """ # Indicates if the implemented serializer is only available for # internal Django use. internal_use_only = False progress_class = ProgressBar stream_class = StringIO def serialize(self, queryset, **options): """ Serialize a queryset. """ self.options = options self.stream = options.pop("stream", self.stream_class()) self.selected_fields = options.pop("fields", None) self.use_natural_foreign_keys = options.pop('use_natural_foreign_keys', False) self.use_natural_primary_keys = options.pop('use_natural_primary_keys', False) progress_bar = self.progress_class( options.pop('progress_output', None), options.pop('object_count', 0) ) self.start_serialization() self.first = True for count, obj in enumerate(queryset, start=1): self.start_object(obj) # Use the concrete parent class' _meta instead of the object's _meta # This is to avoid local_fields problems for proxy models. Refs #17717. concrete_model = obj._meta.concrete_model for field in concrete_model._meta.local_fields: if field.serialize: if field.remote_field is None: if self.selected_fields is None or field.attname in self.selected_fields: self.handle_field(obj, field) else: if self.field_is_selected(field) and self.output_pk_field(obj, field): self.handle_fk_field(obj, field) for field in concrete_model._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) progress_bar.update(count) if self.first: self.first = False self.end_serialization() return self.getvalue() def field_is_selected(self, field): return self.selected_fields is None or field.attname[:-3] in self.selected_fields def output_pk_field(self, obj, pk_field): return self.use_natural_primary_keys or pk_field != obj._meta.pk def start_serialization(self): """ Called when serializing of the queryset starts. """ raise NotImplementedError('subclasses of Serializer must provide a start_serialization() method') 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('subclasses of Serializer must provide a start_object() method') 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('subclasses of Serializer must provide an handle_field() method') def handle_fk_field(self, obj, field): """ Called to handle a ForeignKey field. """ raise NotImplementedError('subclasses of Serializer must provide an handle_fk_field() method') def handle_m2m_field(self, obj, field): """ Called to handle a ManyToManyField. """ raise NotImplementedError('subclasses of Serializer must provide an handle_m2m_field() method') def getvalue(self): """ Return the fully serialized queryset (or None if the output stream is not seekable). """ if callable(getattr(self.stream, 'getvalue', None)): return self.stream.getvalue() class Deserializer: """ 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, str): self.stream = StringIO(stream_or_string) else: self.stream = stream_or_string def __iter__(self): return self def __next__(self): """Iteration iterface -- return the next item in the stream""" raise NotImplementedError('subclasses of Deserializer must provide a __next__() method') 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 "<%s: %s(pk=%s)>" % ( self.__class__.__name__, self.object._meta.label, self.object.pk, ) def save(self, save_m2m=True, using=None, **kwargs): # Call save on the Model baseclass directly. This bypasses any # model-defined save. The save is also forced to be raw. # raw=True is passed to any pre/post_save signals. models.Model.save_base(self.object, using=using, raw=True, **kwargs) if self.m2m_data and save_m2m: for accessor_name, object_list in self.m2m_data.items(): getattr(self.object, accessor_name).set(object_list) # prevent a second (possibly accidental) call to save() from saving # the m2m data twice. self.m2m_data = None def build_instance(Model, data, db): """ Build a model instance. If the model instance doesn't have a primary key and the model supports natural keys, try to retrieve it from the database. """ obj = Model(**data) if (obj.pk is None and hasattr(Model, 'natural_key') and hasattr(Model._default_manager, 'get_by_natural_key')): natural_key = obj.natural_key() try: obj.pk = Model._default_manager.db_manager(db).get_by_natural_key(*natural_key).pk except Model.DoesNotExist: pass return obj