philo/models/fields/entities.py

   1 """
   2 EntityProxyFields can be assigned as fields on a subclass of philo.models.Entity. They act like any other model fields, but instead of saving their data to the model's table, they save it to attributes related to a model instance. Additionally, a new attribute will be created for an instance if and only if the field's value has been set. This is relevant i.e. for :class:`QuerySetMapper` passthroughs, where even an Attribute with a value of ``None`` must prevent a passthrough.
   3
   4 Example::
   5
   6         class Thing(Entity):
   7                 numbers = models.PositiveIntegerField()
   8                 improvised = JSONAttribute(models.BooleanField)
   9 """
  10 import datetime
  11 from itertools import tee
  12
  13 from django import forms
  14 from django.core.exceptions import FieldError
  15 from django.db import models
  16 from django.db.models.fields import NOT_PROVIDED
  17 from django.utils.text import capfirst
  18
  19 from philo.models import ManyToManyValue, JSONValue, ForeignKeyValue, Attribute, Entity
  20 from philo.signals import entity_class_prepared
  21
  22
  23 __all__ = ('JSONAttribute', 'ForeignKeyAttribute', 'ManyToManyAttribute')
  24
  25
  26 ATTRIBUTE_REGISTRY = '_attribute_registry'
  27
  28
  29 class EntityProxyField(object):
  30         def __init__(self, verbose_name=None, help_text=None, default=NOT_PROVIDED, editable=True, choices=None, *args, **kwargs):
  31                 self.verbose_name = verbose_name
  32                 self.help_text = help_text
  33                 self.default = default
  34                 self.editable = editable
  35                 self._choices = choices or []
  36
  37         def actually_contribute_to_class(self, sender, **kwargs):
  38                 sender._entity_meta.add_proxy_field(self)
  39
  40         def contribute_to_class(self, cls, name):
  41                 if issubclass(cls, Entity):
  42                         self.name = self.attname = name
  43                         self.model = cls
  44                         if self.verbose_name is None and name:
  45                                 self.verbose_name = name.replace('_', ' ')
  46                         entity_class_prepared.connect(self.actually_contribute_to_class, sender=cls)
  47                 else:
  48                         raise FieldError('%s instances can only be declared on Entity subclasses.' % self.__class__.__name__)
  49
  50         def formfield(self, form_class=forms.CharField, **kwargs):
  51                 defaults = {
  52                         'required': False,
  53                         'label': capfirst(self.verbose_name),
  54                         'help_text': self.help_text
  55                 }
  56                 if self.has_default():
  57                         defaults['initial'] = self.default
  58                 defaults.update(kwargs)
  59                 return form_class(**defaults)
  60
  61         def value_from_object(self, obj):
  62                 """The return value of this method will be used by the EntityForm as
  63                 this field's initial value."""
  64                 return getattr(obj, self.name)
  65
  66         def get_storage_value(self, value):
  67                 """Final conversion of `value` before it gets stored on an Entity instance.
  68                 This step is performed by the ProxyFieldForm."""
  69                 return value
  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         """This function is attached to each :class:`Entity` subclass's post_save signal. Any :class:`Attribute`\ s managed by EntityProxyFields which have been removed will be deleted, and any new attributes will be created """
 122         if ATTRIBUTE_REGISTRY in instance.__dict__:
 123                 registry = instance.__dict__[ATTRIBUTE_REGISTRY]
 124                 instance.attribute_set.filter(key__in=[field.attribute_key for field in registry['removed']]).delete()
 125
 126                 for field in registry['added']:
 127                         try:
 128                                 attribute = instance.attribute_set.get(key=field.attribute_key)
 129                         except Attribute.DoesNotExist:
 130                                 attribute = Attribute()
 131                                 attribute.entity = instance
 132                                 attribute.key = field.attribute_key
 133                         attribute.set_value(value=getattr(instance, field.name, None), value_class=field.value_class)
 134                 del instance.__dict__[ATTRIBUTE_REGISTRY]
 135
 136
 137 class AttributeField(EntityProxyField):
 138         def __init__(self, attribute_key=None, **kwargs):
 139                 self.attribute_key = attribute_key
 140                 super(AttributeField, self).__init__(**kwargs)
 141
 142         def actually_contribute_to_class(self, sender, **kwargs):
 143                 super(AttributeField, self).actually_contribute_to_class(sender, **kwargs)
 144                 setattr(sender, self.name, AttributeFieldDescriptor(self))
 145                 opts = sender._entity_meta
 146                 if not hasattr(opts, '_has_attribute_fields'):
 147                         opts._has_attribute_fields = True
 148                         models.signals.post_save.connect(process_attribute_fields, sender=sender)
 149
 150         def contribute_to_class(self, cls, name):
 151                 if self.attribute_key is None:
 152                         self.attribute_key = name
 153                 super(AttributeField, self).contribute_to_class(cls, name)
 154
 155         def validate_value(self, value):
 156                 "Confirm that the value is valid or raise an appropriate error."
 157                 pass
 158
 159         @property
 160         def value_class(self):
 161                 raise AttributeError("value_class must be defined on AttributeField subclasses.")
 162
 163
 164 class JSONAttribute(AttributeField):
 165         """Handles an :class:`Attribute` with a :class:`JSONValue`."""
 166
 167         value_class = JSONValue
 168
 169         def __init__(self, field_template=None, **kwargs):
 170                 super(JSONAttribute, self).__init__(**kwargs)
 171                 if field_template is None:
 172                         field_template = models.CharField(max_length=255)
 173                 self.field_template = field_template
 174
 175         def formfield(self, **kwargs):
 176                 defaults = {
 177                         'required': False,
 178                         'label': capfirst(self.verbose_name),
 179                         'help_text': self.help_text
 180                 }
 181                 if self.has_default():
 182                         defaults['initial'] = self.default
 183                 defaults.update(kwargs)
 184                 return self.field_template.formfield(**defaults)
 185
 186         def value_from_object(self, obj):
 187                 value = super(JSONAttribute, self).value_from_object(obj)
 188                 if isinstance(self.field_template, (models.DateField, models.DateTimeField)):
 189                         value = self.field_template.to_python(value)
 190                 return value
 191
 192         def get_storage_value(self, value):
 193                 if isinstance(value, datetime.datetime):
 194                         return value.strftime("%Y-%m-%d %H:%M:%S")
 195                 if isinstance(value, datetime.date):
 196                         return value.strftime("%Y-%m-%d")
 197                 return value
 198
 199
 200 class ForeignKeyAttribute(AttributeField):
 201         """Handles an :class:`Attribute` with a :class:`ForeignKeyValue`."""
 202         value_class = ForeignKeyValue
 203
 204         def __init__(self, model, limit_choices_to=None, **kwargs):
 205                 super(ForeignKeyAttribute, self).__init__(**kwargs)
 206                 self.to = 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.to) :
 213                         raise TypeError("The '%s' attribute can only be set to an instance of %s or None." % (self.name, self.to.__name__))
 214
 215         def formfield(self, form_class=forms.ModelChoiceField, **kwargs):
 216                 defaults = {
 217                         'queryset': self.to._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         def get_related_field(self):
 227                 """Spoof being a rel from a ForeignKey."""
 228                 return self.to._meta.pk
 229
 230
 231 class ManyToManyAttribute(ForeignKeyAttribute):
 232         value_class = ManyToManyValue
 233
 234         def validate_value(self, value):
 235                 if not isinstance(value, models.query.QuerySet) or value.model != self.to:
 236                         raise TypeError("The '%s' attribute can only be set to a %s QuerySet." % (self.name, self.to.__name__))
 237
 238         def formfield(self, form_class=forms.ModelMultipleChoiceField, **kwargs):
 239                 return super(ManyToManyAttribute, self).formfield(form_class=form_class, **kwargs)
 240
 241         def value_from_object(self, obj):
 242                 qs = super(ForeignKeyAttribute, self).value_from_object(obj)
 243                 try:
 244                         return qs.values_list('pk', flat=True)
 245                 except:
 246                         return []