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""" Customizable serialization. """ from django.db import models from django.db.models.query import QuerySet from django.db.models.fields.related import RelatedField from django.utils.encoding import smart_unicode, is_protected_type import decimal import inspect import types # We register serializer classes, so that we can refer to them by their # class names, if there are cyclical serialization heirachys. _serializers = {} def _field_to_tuple(field): """ Convert an item in the `fields` attribute into a 2-tuple. """ if isinstance(field, (tuple, list)): return (field[0], field[1]) return (field, None) def _fields_to_list(fields): """ Return a list of field names. """ return [_field_to_tuple(field)[0] for field in fields or ()] def _fields_to_dict(fields): """ Return a `dict` of field name -> None, or tuple of fields, or Serializer class """ return dict([_field_to_tuple(field) for field in fields or ()]) class _SkipField(Exception): """ Signals that a serialized field should be ignored. We use this mechanism as the default behavior for ensuring that we don't infinitely recurse when dealing with nested data. """ pass class _RegisterSerializer(type): """ Metaclass to register serializers. """ def __new__(cls, name, bases, attrs): # Build the class and register it. ret = super(_RegisterSerializer, cls).__new__(cls, name, bases, attrs) _serializers[name] = ret return ret class Serializer(object): """ Converts python objects into plain old native types suitable for serialization. In particular it handles models and querysets. The output format is specified by setting a number of attributes on the class. You may also override any of the serialization methods, to provide for more flexible behavior. Valid output types include anything that may be directly rendered into json, xml etc... """ __metaclass__ = _RegisterSerializer fields = () """ Specify the fields to be serialized on a model or dict. Overrides `include` and `exclude`. """ include = () """ Fields to add to the default set to be serialized on a model/dict. """ exclude = () """ Fields to remove from the default set to be serialized on a model/dict. """ rename = {} """ A dict of key->name to use for the field keys. """ related_serializer = None """ The default serializer class to use for any related models. """ depth = None """ The maximum depth to serialize to, or `None`. """ def __init__(self, depth=None, stack=[], **kwargs): self.depth = depth or self.depth self.stack = stack def get_fields(self, obj): """ Return the set of field names/keys to use for a model instance/dict. """ fields = self.fields # If `fields` is not set, we use the default fields and modify # them with `include` and `exclude` if not fields: default = self.get_default_fields(obj) include = self.include or () exclude = self.exclude or () fields = set(default + list(include)) - set(exclude) else: fields = _fields_to_list(self.fields) return fields def get_default_fields(self, obj): """ Return the default list of field names/keys for a model instance/dict. These are used if `fields` is not given. """ if isinstance(obj, models.Model): opts = obj._meta return [field.name for field in opts.fields + opts.many_to_many] else: return obj.keys() def get_related_serializer(self, key): info = _fields_to_dict(self.fields).get(key, None) # If an element in `fields` is a 2-tuple of (str, tuple) # then the second element of the tuple is the fields to # set on the related serializer if isinstance(info, (list, tuple)): class OnTheFlySerializer(Serializer): fields = info return OnTheFlySerializer # If an element in `fields` is a 2-tuple of (str, Serializer) # then the second element of the tuple is the Serializer # class to use for that field. elif isinstance(info, type) and issubclass(info, Serializer): return info # If an element in `fields` is a 2-tuple of (str, str) # then the second element of the tuple is the name of the Serializer # class to use for that field. # # Black magic to deal with cyclical Serializer dependancies. # Similar to what Django does for cyclically related models. elif isinstance(info, str) and info in _serializers: return _serializers[info] # Otherwise use `related_serializer` or fall back to `Serializer` return getattr(self, 'related_serializer') or Serializer def serialize_key(self, key): """ Keys serialize to their string value, unless they exist in the `rename` dict. """ return getattr(self.rename, key, key) def serialize_val(self, key, obj): """ Convert a model field or dict value into a serializable representation. """ related_serializer = self.get_related_serializer(key) if self.depth is None: depth = None elif self.depth <= 0: return self.serialize_max_depth(obj) else: depth = self.depth - 1 if any([obj is elem for elem in self.stack]): return self.serialize_recursion(obj) else: stack = self.stack[:] stack.append(obj) return related_serializer(depth=depth, stack=stack).serialize(obj) def serialize_max_depth(self, obj): """ Determine how objects should be serialized once `depth` is exceeded. The default behavior is to ignore the field. """ raise _SkipField def serialize_recursion(self, obj): """ Determine how objects should be serialized if recursion occurs. The default behavior is to ignore the field. """ raise _SkipField def serialize_model(self, instance): """ Given a model instance or dict, serialize it to a dict.. """ data = {} fields = self.get_fields(instance) # serialize each required field for fname in fields: if hasattr(self, fname): # check for a method 'fname' on self first meth = getattr(self, fname) if inspect.ismethod(meth) and len(inspect.getargspec(meth)[0]) == 2: obj = meth(instance) elif hasattr(instance, fname): # now check for an attribute 'fname' on the instance obj = getattr(instance, fname) elif fname in instance: # finally check for a key 'fname' on the instance obj = instance[fname] else: continue try: key = self.serialize_key(fname) val = self.serialize_val(fname, obj) data[key] = val except _SkipField: pass return data def serialize_iter(self, obj): """ Convert iterables into a serializable representation. """ return [self.serialize(item) for item in obj] def serialize_func(self, obj): """ Convert no-arg methods and functions into a serializable representation. """ return self.serialize(obj()) def serialize_manager(self, obj): """ Convert a model manager into a serializable representation. """ return self.serialize_iter(obj.all()) def serialize_fallback(self, obj): """ Convert any unhandled object into a serializable representation. """ return smart_unicode(obj, strings_only=True) def serialize(self, obj): """ Convert any object into a serializable representation. """ if isinstance(obj, (dict, models.Model)): # Model instances & dictionaries return self.serialize_model(obj) elif isinstance(obj, (tuple, list, set, QuerySet, types.GeneratorType)): # basic iterables return self.serialize_iter(obj) elif isinstance(obj, models.Manager): # Manager objects return self.serialize_manager(obj) elif inspect.isfunction(obj) and not inspect.getargspec(obj)[0]: # function with no args return self.serialize_func(obj) elif inspect.ismethod(obj) and len(inspect.getargspec(obj)[0]) <= 1: # bound method return self.serialize_func(obj) # Protected types are passed through as is. # (i.e. Primitives like None, numbers, dates, and Decimals.) if is_protected_type(obj): return obj # All other values are converted to string. return self.serialize_fallback(obj)


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