fields.py

from django.db import models

try:
	import cPickle as pickle
except ImportError:
	import pickle

import base64

class PickledObject(str):
	"""A subclass of string so it can be told whether a string is
	   a pickled object or not (if the object is an instance of this class
	   then it must [well, should] be a pickled one)."""
	pass

class PickledObjectField(models.Field):
	__metaclass__ = models.SubfieldBase
	
	def to_python(self, value):
		if isinstance(value, PickledObject):
			# If the value is a definite pickle; and an error is raised in de-pickling
			# it should be allowed to propogate.
			return pickle.loads(str(value))
		else:
			try:
				return pickle.loads(str(value))
			except:
				# If an error was raised, just return the plain value
				return value
	
	def get_db_prep_save(self, value):
		if value is not None and not isinstance(value, PickledObject):
			value = PickledObject(pickle.dumps(value))
		return value
	
	def get_internal_type(self): 
		return 'TextField'
	
	def get_db_prep_lookup(self, lookup_type, value):
		if lookup_type == 'exact':
			value = self.get_db_prep_save(value)
			return super(PickledObjectField, self).get_db_prep_lookup(lookup_type, value)
		elif lookup_type == 'in':
			value = [self.get_db_prep_save(v) for v in value]
			return super(PickledObjectField, self).get_db_prep_lookup(lookup_type, value)
		else:
			raise TypeError('Lookup type %s is not supported.' % lookup_type)

class DictionaryField(models.Field):
	# Django seems to do some funky stuff prohibiting this class from inheriting from
	# PickledObjectField which I can't be bothered to explore. This is quicker, but not DRY :-(
	__metaclass__ = models.SubfieldBase
	
	def to_python(self, value):
		if isinstance(value, dict):
			return value
		else:
			if not value:
				return value
			return pickle.loads(str(value))
	
	def get_db_prep_save(self, value):
		if value is not None and not isinstance(value, basestring):
			if isinstance(value, dict):
				value = pickle.dumps(value)
			else:
				raise TypeError('This field can only store dictionaries. Use PickledObjectField to store a wide(r) range of data types.')
		return value
	
	def get_internal_type(self): 
		return 'TextField'
	
	def get_db_prep_lookup(self, lookup_type, value):
		if lookup_type == 'exact':
			value = self.get_db_prep_save(value)
			return super(DictionaryField, self).get_db_prep_lookup(lookup_type, value)
		elif lookup_type == 'in':
			value = [self.get_db_prep_save(v) for v in value]
			return super(DictionaryField, self).get_db_prep_lookup(lookup_type, value)
		else:
			raise TypeError('Lookup type %s is not supported.' % lookup_type)

class ListField(models.Field):
	"""A field for storing a list (or tuple) in the database."""
	__metaclass__ = models.SubfieldBase
	
	def to_python(self, value):
		if isinstance(value, (list, tuple)):
			return value
		else:
			if not value:
				return value
			try:
				return base64.b64decode(pickle.loads(str(value)))
			except:
				return []
	
	def get_db_prep_save(self, value):
		if value is not None and not isinstance(value, basestring):
			if isinstance(value, (list, tuple)):
				value = base64.b64encode(pickle.dumps(value))
			else:
				raise TypeError('This field can only store lists or tuples. Use PickledObjectField to store a wide(r) range of data types.')
		return value
	
	def get_internal_type(self): 
		return 'TextField'
	
	def get_db_prep_lookup(self, lookup_type, value):
		if lookup_type == 'exact':
			value = self.get_db_prep_save(value)
			return super(DictionaryField, self).get_db_prep_lookup(lookup_type, value)
		elif lookup_type == 'in':
			value = [self.get_db_prep_save(v) for v in value]
			return super(DictionaryField, self).get_db_prep_lookup(lookup_type, value)
		else:
			raise TypeError('Lookup type %s is not supported.' % lookup_type)