contrib/cowell/fields.py

   1 """
   2 The Attributes defined in this file can be assigned as fields on a
   3 subclass of philo.models.Entity. They act like any other model fields,
   4 but instead of saving their data to the database, they save it to
   5 attributes related to a model instance. Additionally, a new attribute will
   6 be created for an instance if and only if the field's value has been set.
   7 This is relevant i.e. for passthroughs, where the value of the field may
   8 be defined by some other instance's attributes.
   9
  10 Example::
  11
  12         class Thing(Entity):
  13                 numbers = models.PositiveIntegerField()
  14
  15         class ThingProxy(Thing):
  16                 improvised = JSONAttribute(models.BooleanField)
  17 """
  18 from itertools import tee
  19 from django import forms
  20 from django.core.exceptions import FieldError
  21 from django.db import models
  22 from django.db.models.fields import NOT_PROVIDED
  23 from django.utils.text import capfirst
  24 from philo.signals import entity_class_prepared
  25 from philo.models import ManyToManyValue, JSONValue, ForeignKeyValue, Attribute, Entity
  26
  27
  28 __all__ = ('JSONAttribute', 'ForeignKeyAttribute', 'ManyToManyAttribute')
  29
  30
  31 ATTRIBUTE_REGISTRY = '_attribute_registry'
  32
  33
  34 class EntityProxyField(object):
  35         def __init__(self, verbose_name=None, help_text=None, default=NOT_PROVIDED, editable=True, choices=None, *args, **kwargs):
  36                 self.verbose_name = verbose_name
  37                 self.help_text = help_text
  38                 self.default = default
  39                 self.editable = editable
  40                 self._choices = choices or []
  41
  42         def actually_contribute_to_class(self, sender, **kwargs):
  43                 sender._entity_meta.add_proxy_field(self)
  44
  45         def contribute_to_class(self, cls, name):
  46                 if issubclass(cls, Entity):
  47                         self.name = self.attname = name
  48                         self.model = cls
  49                         if self.verbose_name is None and name:
  50                                 self.verbose_name = name.replace('_', ' ')
  51                         entity_class_prepared.connect(self.actually_contribute_to_class, sender=cls)
  52                 else:
  53                         raise FieldError('%s instances can only be declared on Entity subclasses.' % self.__class__.__name__)
  54
  55         def formfield(self, form_class=forms.CharField, **kwargs):
  56                 defaults = {
  57                         'required': False,
  58                         'label': capfirst(self.verbose_name),
  59                         'help_text': self.help_text
  60                 }
  61                 if self.has_default():
  62                         defaults['initial'] = self.default
  63                 defaults.update(kwargs)
  64                 return form_class(**defaults)
  65
  66         def value_from_object(self, obj):
  67                 """The return value of this method will be used by the EntityForm as
  68                 this field's initial value."""
  69                 return getattr(obj, self.name)
  70
  71         def has_default(self):
  72                 return self.default is not NOT_PROVIDED
  73
  74         def _get_choices(self):
  75                 if hasattr(self._choices, 'next'):
  76                         choices, self._choices = tee(self._choices)
  77                         return choices
  78                 else:
  79                         return self._choices
  80         choices = property(_get_choices)
  81
  82
  83 class AttributeFieldDescriptor(object):
  84         def __init__(self, field):
  85                 self.field = field
  86
  87         def get_registry(self, instance):
  88                 if ATTRIBUTE_REGISTRY not in instance.__dict__:
  89                         instance.__dict__[ATTRIBUTE_REGISTRY] = {'added': set(), 'removed': set()}
  90                 return instance.__dict__[ATTRIBUTE_REGISTRY]
  91
  92         def __get__(self, instance, owner):
  93                 if instance is None:
  94                         return self
  95
  96                 if self.field.name not in instance.__dict__:
  97                         instance.__dict__[self.field.name] = instance.attributes.get(self.field.attribute_key, None)
  98
  99                 return instance.__dict__[self.field.name]
 100
 101         def __set__(self, instance, value):
 102                 if instance is None:
 103                         raise AttributeError("%s must be accessed via instance" % self.field.name)
 104
 105                 self.field.validate_value(value)
 106                 instance.__dict__[self.field.name] = value
 107
 108                 registry = self.get_registry(instance)
 109                 registry['added'].add(self.field)
 110                 registry['removed'].discard(self.field)
 111
 112         def __delete__(self, instance):
 113                 del instance.__dict__[self.field.name]
 114
 115                 registry = self.get_registry(instance)
 116                 registry['added'].discard(self.field)
 117                 registry['removed'].add(self.field)
 118
 119
 120 def process_attribute_fields(sender, instance, created, **kwargs):
 121         if ATTRIBUTE_REGISTRY in instance.__dict__:
 122                 registry = instance.__dict__[ATTRIBUTE_REGISTRY]
 123                 instance.attribute_set.filter(key__in=[field.attribute_key for field in registry['removed']]).delete()
 124
 125                 for field in registry['added']:
 126                         try:
 127                                 attribute = instance.attribute_set.get(key=field.attribute_key)
 128                         except Attribute.DoesNotExist:
 129                                 attribute = Attribute()
 130                                 attribute.entity = instance
 131                                 attribute.key = field.attribute_key
 132
 133                         value_class = field.value_class
 134                         if isinstance(attribute.value, value_class):
 135                                 value = attribute.value
 136                         else:
 137                                 if isinstance(attribute.value, models.Model):
 138                                         attribute.value.delete()
 139                                 value = value_class()
 140
 141                         value.set_value(getattr(instance, field.name, None))
 142                         value.save()
 143
 144                         attribute.value = value
 145                         attribute.save()
 146                 del instance.__dict__[ATTRIBUTE_REGISTRY]
 147
 148
 149 class AttributeField(EntityProxyField):
 150         def __init__(self, attribute_key=None, **kwargs):
 151                 self.attribute_key = attribute_key
 152                 super(AttributeField, self).__init__(**kwargs)
 153
 154         def actually_contribute_to_class(self, sender, **kwargs):
 155                 super(AttributeField, self).actually_contribute_to_class(sender, **kwargs)
 156                 setattr(sender, self.name, AttributeFieldDescriptor(self))
 157                 opts = sender._entity_meta
 158                 if not hasattr(opts, '_has_attribute_fields'):
 159                         opts._has_attribute_fields = True
 160                         models.signals.post_save.connect(process_attribute_fields, sender=sender)
 161
 162
 163         def contribute_to_class(self, cls, name):
 164                 if self.attribute_key is None:
 165                         self.attribute_key = name
 166                 super(AttributeField, self).contribute_to_class(cls, name)
 167
 168         def validate_value(self, value):
 169                 "Confirm that the value is valid or raise an appropriate error."
 170                 raise NotImplementedError("validate_value must be implemented by AttributeField subclasses.")
 171
 172         @property
 173         def value_class(self):
 174                 raise AttributeError("value_class must be defined on AttributeField subclasses.")
 175
 176
 177 class JSONAttribute(AttributeField):
 178         value_class = JSONValue
 179
 180         def __init__(self, field_template=None, **kwargs):
 181                 super(JSONAttribute, self).__init__(**kwargs)
 182                 if field_template is None:
 183                         field_template = models.CharField(max_length=255)
 184                 self.field_template = field_template
 185
 186         def validate_value(self, value):
 187                 pass
 188
 189         def formfield(self, **kwargs):
 190                 defaults = {
 191                         'required': False,
 192                         'label': capfirst(self.verbose_name),
 193                         'help_text': self.help_text
 194                 }
 195                 if self.has_default():
 196                         defaults['initial'] = self.default
 197                 defaults.update(kwargs)
 198                 return self.field_template.formfield(**defaults)
 199
 200
 201 class ForeignKeyAttribute(AttributeField):
 202         value_class = ForeignKeyValue
 203
 204         def __init__(self, model, limit_choices_to=None, **kwargs):
 205                 super(ForeignKeyAttribute, self).__init__(**kwargs)
 206                 self.model = model
 207                 if limit_choices_to is None:
 208                         limit_choices_to = {}
 209                 self.limit_choices_to = limit_choices_to
 210
 211         def validate_value(self, value):
 212                 if value is not None and not isinstance(value, self.model) :
 213                         raise TypeError("The '%s' attribute can only be set to an instance of %s or None." % (self.name, self.model.__name__))
 214
 215         def formfield(self, form_class=forms.ModelChoiceField, **kwargs):
 216                 defaults = {
 217                         'queryset': self.model._default_manager.complex_filter(self.limit_choices_to)
 218                 }
 219                 defaults.update(kwargs)
 220                 return super(ForeignKeyAttribute, self).formfield(form_class=form_class, **defaults)
 221
 222         def value_from_object(self, obj):
 223                 relobj = super(ForeignKeyAttribute, self).value_from_object(obj)
 224                 return getattr(relobj, 'pk', None)
 225
 226         @property
 227         def to(self):
 228                 """Spoof being a rel from a ForeignKey."""
 229                 return self.model
 230
 231         def get_related_field(self):
 232                 """Again, spoof being a rel from a ForeignKey."""
 233                 return self.model._meta.pk
 234
 235
 236 class ManyToManyAttribute(ForeignKeyAttribute):
 237         value_class = ManyToManyValue
 238
 239         def validate_value(self, value):
 240                 if not isinstance(value, models.query.QuerySet) or value.model != self.model:
 241                         raise TypeError("The '%s' attribute can only be set to a %s QuerySet." % (self.name, self.model.__name__))
 242
 243         def formfield(self, form_class=forms.ModelMultipleChoiceField, **kwargs):
 244                 return super(ManyToManyAttribute, self).formfield(form_class=form_class, **kwargs)
 245
 246         def value_from_object(self, obj):
 247                 qs = super(ForeignKeyAttribute, self).value_from_object(obj)
 248                 try:
 249                         return qs.values_list('pk', flat=True)
 250                 except:
 251                         return []