django rest framework 反序列化过程剖析
前天写了序列化过程，今天就水一篇反序列化过程吧。
反序列化一般都在create,update方法中被使用，如：
class CreateModelMixin: """ Create a model instance. """ def create(self, request, *args, **kwargs): serializer = self.get_serializer(data=request.data) serializer.is_valid(raise_exception=True) self.perform_create(serializer) headers = self.get_success_headers(serializer.data) return Response(serializer.data, status=status.HTTP_201_CREATED, headers=headers) def perform_create(self, serializer): serializer.save() def get_success_headers(self, data): try: return {'Location': str(data[api_settings.URL_FIELD_NAME])} except (TypeError, KeyError): return {}
根据前天所述的继承关系这里serializer.is_valid()调用的就是rest_framework.serilizers.BaseSerializer的is_valid方法，用该方法去反序列化去检查输入的数据是不是符合serilizer类中定义的数据格式
class BaseSerializer(Field): def is_valid(self, raise_exception=False): assert not hasattr(self, 'restore_object'), ( 'Serializer `%s.%s` has old-style version 2 `.restore_object()` ' 'that is no longer compatible with REST framework 3. ' 'Use the new-style `.create()` and `.update()` methods instead.' % (self.__class__.__module__, self.__class__.__name__) ) assert hasattr(self, 'initial_data'), ( 'Cannot call `.is_valid()` as no `data=` keyword argument was ' 'passed when instantiating the serializer instance.' ) if not hasattr(self, '_validated_data'): try: self._validated_data = self.run_validation(self.initial_data) except ValidationError as exc: self._validated_data = {} self._errors = exc.detail else: self._errors = {} if self._errors and raise_exception: raise ValidationError(self.errors) return not bool(self._errors)
run_validation方法在rest_framework.serilizers.Serializer类中被定义
class Serializer(BaseSerializer, metaclass=SerializerMetaclass): def run_validation(self, data=empty): """ We override the default `run_validation`, because the validation performed by validators and the `.validate()` method should be coerced into an error dictionary with a 'non_fields_error' key. """ (is_empty_value, data) = self.validate_empty_values(data) if is_empty_value: return data value = self.to_internal_value(data) try: self.run_validators(value) value = self.validate(value) assert value is not None, '.validate() should return the validated data' except (ValidationError, DjangoValidationError) as exc: raise ValidationError(detail=as_serializer_error(exc)) return value def run_validators(self, value): """ Add read_only fields with defaults to value before running validators. """ if isinstance(value, dict): to_validate = self._read_only_defaults() to_validate.update(value) else: to_validate = value super().run_validators(to_validate) def to_internal_value(self, data): """ Dict of native values <- Dict of primitive datatypes. """ if not isinstance(data, Mapping): message = self.error_messages['invalid'].format( datatype=type(data).__name__ ) raise ValidationError({ api_settings.NON_FIELD_ERRORS_KEY: [message] }, code='invalid') ret = OrderedDict() errors = OrderedDict() fields = self._writable_fields for field in fields: validate_method = getattr(self, 'validate_' + field.field_name, None) primitive_value = field.get_value(data) try: validated_value = field.run_validation(primitive_value) if validate_method is not None: validated_value = validate_method(validated_value) except ValidationError as exc: errors[field.field_name] = exc.detail except DjangoValidationError as exc: errors[field.field_name] = get_error_detail(exc) except SkipField: pass else: set_value(ret, field.source_attrs, validated_value) if errors: raise ValidationError(errors) return ret
在to_internal_value中对字段做反序列化校验，然后在run_validators中对serilizers类中定义的validators规则做校验
校验通过后使用serializer.save保存数据，serializer.save()调用的就是rest_framework.serilizers.BaseSerializer的save方法
class BaseSerializer(Field): def save(self, **kwargs): assert not hasattr(self, 'save_object'), ( 'Serializer `%s.%s` has old-style version 2 `.save_object()` ' 'that is no longer compatible with REST framework 3. ' 'Use the new-style `.create()` and `.update()` methods instead.' % (self.__class__.__module__, self.__class__.__name__) ) assert hasattr(self, '_errors'), ( 'You must call `.is_valid()` before calling `.save()`.' ) assert not self.errors, ( 'You cannot call `.save()` on a serializer with invalid data.' ) # Guard against incorrect use of `serializer.save(commit=False)` assert 'commit' not in kwargs, ( "'commit' is not a valid keyword argument to the 'save()' method. " "If you need to access data before committing to the database then " "inspect 'serializer.validated_data' instead. " "You can also pass additional keyword arguments to 'save()' if you " "need to set extra attributes on the saved model instance. " "For example: 'serializer.save(owner=request.user)'.'" ) assert not hasattr(self, '_data'), ( "You cannot call `.save()` after accessing `serializer.data`." "If you need to access data before committing to the database then " "inspect 'serializer.validated_data' instead. " ) validated_data = dict( list(self.validated_data.items()) + list(kwargs.items()) ) if self.instance is not None: self.instance = self.update(self.instance, validated_data) assert self.instance is not None, ( '`update()` did not return an object instance.' ) else: self.instance = self.create(validated_data) assert self.instance is not None, ( '`create()` did not return an object instance.' ) return self.instance
在这里用self.instance判断是不是创建还是更新（即是create还是update）所以也会调用相应的方法，就拿create来说
在这里调用的就是rest_framework.serilizers.ModelSerializer类的create方法（update时也是同理）
class ModelSerializer(Serializer): def create(self, validated_data): """ We have a bit of extra checking around this in order to provide descriptive messages when something goes wrong, but this method is essentially just: return ExampleModel.objects.create(**validated_data) If there are many to many fields present on the instance then they cannot be set until the model is instantiated, in which case the implementation is like so: example_relationship = validated_data.pop('example_relationship') instance = ExampleModel.objects.create(**validated_data) instance.example_relationship = example_relationship return instance The default implementation also does not handle nested relationships. If you want to support writable nested relationships you'll need to write an explicit `.create()` method. """ raise_errors_on_nested_writes('create', self, validated_data) ModelClass = self.Meta.model # Remove many-to-many relationships from validated_data. # They are not valid arguments to the default `.create()` method, # as they require that the instance has already been saved. info = model_meta.get_field_info(ModelClass) many_to_many = {} for field_name, relation_info in info.relations.items(): if relation_info.to_many and (field_name in validated_data): many_to_many[field_name] = validated_data.pop(field_name) try: instance = ModelClass._default_manager.create(**validated_data) except TypeError: tb = traceback.format_exc() msg = ( 'Got a `TypeError` when calling `%s.%s.create()`. ' 'This may be because you have a writable field on the ' 'serializer class that is not a valid argument to ' '`%s.%s.create()`. You may need to make the field ' 'read-only, or override the %s.create() method to handle ' 'this correctly.\nOriginal exception was:\n %s' % ( ModelClass.__name__, ModelClass._default_manager.name, ModelClass.__name__, ModelClass._default_manager.name, self.__class__.__name__, tb ) ) raise TypeError(msg) # Save many-to-many relationships after the instance is created. if many_to_many: for field_name, value in many_to_many.items(): field = getattr(instance, field_name) field.set(value) return instance def update(self, instance, validated_data): raise_errors_on_nested_writes('update', self, validated_data) info = model_meta.get_field_info(instance) # Simply set each attribute on the instance, and then save it. # Note that unlike `.create()` we don't need to treat many-to-many # relationships as being a special case. During updates we already # have an instance pk for the relationships to be associated with. m2m_fields = [] for attr, value in validated_data.items(): if attr in info.relations and info.relations[attr].to_many: m2m_fields.append((attr, value)) else: setattr(instance, attr, value) instance.save() # Note that many-to-many fields are set after updating instance. # Setting m2m fields triggers signals which could potentially change # updated instance and we do not want it to collide with .update() for attr, value in m2m_fields: field = getattr(instance, attr) field.set(value) return instance
注意了这里self.Meta.model是在serilizer类中定义了的数据库模型类
这里调用_default_manager.create去将数据保存到数据库
