models/fields/entities.py

   1 """
   2 The EntityProxyFields defined in this file can be assigned as fields on
   3 a subclass of philo.models.Entity. They act like any other model
   4 fields, but instead of saving their data to the database, they save it
   5 to attributes related to a model instance. Additionally, a new
   6 attribute will be created for an instance if and only if the field's
   7 value has been set. This is relevant i.e. for passthroughs, where the
   8 value of the field may 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 import datetime
  27
  28
  29 __all__ = ('JSONAttribute', 'ForeignKeyAttribute', 'ManyToManyAttribute')
  30
  31
  32 ATTRIBUTE_REGISTRY = '_attribute_registry'
  33
  34
  35 class EntityProxyField(object):
  36         def __init__(self, verbose_name=None, help_text=None, default=NOT_PROVIDED, editable=True, choices=None, *args, **kwargs):
  37                 self.verbose_name = verbose_name
  38                 self.help_text = help_text
  39                 self.default = default
  40                 self.editable = editable
  41                 self._choices = choices or []
  42
  43         def actually_contribute_to_class(self, sender, **kwargs):
  44                 sender._entity_meta.add_proxy_field(self)
  45
  46         def contribute_to_class(self, cls, name):
  47                 if issubclass(cls, Entity):
  48                         self.name = self.attname = name
  49                         self.model = cls
  50                         if self.verbose_name is None and name:
  51                                 self.verbose_name = name.replace('_', ' ')
  52                         entity_class_prepared.connect(self.actually_contribute_to_class, sender=cls)
  53                 else:
  54                         raise FieldError('%s instances can only be declared on Entity subclasses.' % self.__class__.__name__)
  55
  56         def formfield(self, form_class=forms.CharField, **kwargs):
  57                 defaults = {
  58                         'required': False,
  59                         'label': capfirst(self.verbose_name),
  60                         'help_text': self.help_text
  61                 }
  62                 if self.has_default():
  63                         defaults['initial'] = self.default
  64                 defaults.update(kwargs)
  65                 return form_class(**defaults)
  66
  67         def value_from_object(self, obj):
  68                 """The return value of this method will be used by the EntityForm as
  69                 this field's initial value."""
  70                 return getattr(obj, self.name)
  71
  72         def get_storage_value(self, value):
  73                 """Final conversion of `value` before it gets stored on an Entity instance.
  74                 This step is performed by the ProxyFieldForm."""
  75                 return value
  76
  77         def has_default(self):
  78                 return self.default is not NOT_PROVIDED
  79
  80         def _get_choices(self):
  81                 if hasattr(self._choices, 'next'):
  82                         choices, self._choices = tee(self._choices)
  83                         return choices
  84                 else:
  85                         return self._choices
  86         choices = property(_get_choices)
  87
  88
  89 class AttributeFieldDescriptor(object):
  90         def __init__(self, field):
  91                 self.field = field
  92
  93         def get_registry(self, instance):
  94                 if ATTRIBUTE_REGISTRY not in instance.__dict__:
  95                         instance.__dict__[ATTRIBUTE_REGISTRY] = {'added': set(), 'removed': set()}
  96                 return instance.__dict__[ATTRIBUTE_REGISTRY]
  97
  98         def __get__(self, instance, owner):
  99                 if instance is None:
 100                         return self
 101
 102                 if self.field.name not in instance.__dict__:
 103                         instance.__dict__[self.field.name] = instance.attributes.get(self.field.attribute_key, None)
 104
 105                 return instance.__dict__[self.field.name]
 106
 107         def __set__(self, instance, value):
 108                 if instance is None:
 109                         raise AttributeError("%s must be accessed via instance" % self.field.name)
 110
 111                 self.field.validate_value(value)
 112                 instance.__dict__[self.field.name] = value
 113
 114                 registry = self.get_registry(instance)
 115                 registry['added'].add(self.field)
 116                 registry['removed'].discard(self.field)
 117
 118         def __delete__(self, instance):
 119                 del instance.__dict__[self.field.name]
 120
 121                 registry = self.get_registry(instance)
 122                 registry['added'].discard(self.field)
 123                 registry['removed'].add(self.field)
 124
 125
 126 def process_attribute_fields(sender, instance, created, **kwargs):
 127         if ATTRIBUTE_REGISTRY in instance.__dict__:
 128                 registry = instance.__dict__[ATTRIBUTE_REGISTRY]
 129                 instance.attribute_set.filter(key__in=[field.attribute_key for field in registry['removed']]).delete()
 130
 131                 for field in registry['added']:
 132                         try:
 133                                 attribute = instance.attribute_set.get(key=field.attribute_key)
 134                         except Attribute.DoesNotExist:
 135                                 attribute = Attribute()
 136                                 attribute.entity = instance
 137                                 attribute.key = field.attribute_key
 138
 139                         value_class = field.value_class
 140                         if isinstance(attribute.value, value_class):
 141                                 value = attribute.value
 142                         else:
 143                                 if isinstance(attribute.value, models.Model):
 144                                         attribute.value.delete()
 145                                 value = value_class()
 146
 147                         value.set_value(getattr(instance, field.name, None))
 148                         value.save()
 149
 150                         attribute.value = value
 151                         attribute.save()
 152                 del instance.__dict__[ATTRIBUTE_REGISTRY]
 153
 154
 155 class AttributeField(EntityProxyField):
 156         def __init__(self, attribute_key=None, **kwargs):
 157                 self.attribute_key = attribute_key
 158                 super(AttributeField, self).__init__(**kwargs)
 159
 160         def actually_contribute_to_class(self, sender, **kwargs):
 161                 super(AttributeField, self).actually_contribute_to_class(sender, **kwargs)
 162                 setattr(sender, self.name, AttributeFieldDescriptor(self))
 163                 opts = sender._entity_meta
 164                 if not hasattr(opts, '_has_attribute_fields'):
 165                         opts._has_attribute_fields = True
 166                         models.signals.post_save.connect(process_attribute_fields, sender=sender)
 167
 168         def contribute_to_class(self, cls, name):
 169                 if self.attribute_key is None:
 170                         self.attribute_key = name
 171                 super(AttributeField, self).contribute_to_class(cls, name)
 172
 173         def validate_value(self, value):
 174                 "Confirm that the value is valid or raise an appropriate error."
 175                 pass
 176
 177         @property
 178         def value_class(self):
 179                 raise AttributeError("value_class must be defined on AttributeField subclasses.")
 180
 181
 182 class JSONAttribute(AttributeField):
 183         value_class = JSONValue
 184
 185         def __init__(self, field_template=None, **kwargs):
 186                 super(JSONAttribute, self).__init__(**kwargs)
 187                 if field_template is None:
 188                         field_template = models.CharField(max_length=255)
 189                 self.field_template = field_template
 190
 191         def formfield(self, **kwargs):
 192                 defaults = {
 193                         'required': False,
 194                         'label': capfirst(self.verbose_name),
 195                         'help_text': self.help_text
 196                 }
 197                 if self.has_default():
 198                         defaults['initial'] = self.default
 199                 defaults.update(kwargs)
 200                 return self.field_template.formfield(**defaults)
 201
 202         def value_from_object(self, obj):
 203                 value = super(JSONAttribute, self).value_from_object(obj)
 204                 if isinstance(self.field_template, (models.DateField, models.DateTimeField)):
 205                         value = self.field_template.to_python(value)
 206                 return value
 207
 208         def get_storage_value(self, value):
 209                 if isinstance(value, datetime.datetime):
 210                         return value.strftime("%Y-%m-%d %H:%M:%S")
 211                 if isinstance(value, datetime.date):
 212                         return value.strftime("%Y-%m-%d")
 213                 return value
 214
 215
 216 class ForeignKeyAttribute(AttributeField):
 217         value_class = ForeignKeyValue
 218
 219         def __init__(self, model, limit_choices_to=None, **kwargs):
 220                 super(ForeignKeyAttribute, self).__init__(**kwargs)
 221                 self.to = model
 222                 if limit_choices_to is None:
 223                         limit_choices_to = {}
 224                 self.limit_choices_to = limit_choices_to
 225
 226         def validate_value(self, value):
 227                 if value is not None and not isinstance(value, self.to) :
 228                         raise TypeError("The '%s' attribute can only be set to an instance of %s or None." % (self.name, self.to.__name__))
 229
 230         def formfield(self, form_class=forms.ModelChoiceField, **kwargs):
 231                 defaults = {
 232                         'queryset': self.to._default_manager.complex_filter(self.limit_choices_to)
 233                 }
 234                 defaults.update(kwargs)
 235                 return super(ForeignKeyAttribute, self).formfield(form_class=form_class, **defaults)
 236
 237         def value_from_object(self, obj):
 238                 relobj = super(ForeignKeyAttribute, self).value_from_object(obj)
 239                 return getattr(relobj, 'pk', None)
 240
 241         def get_related_field(self):
 242                 """Spoof being a rel from a ForeignKey."""
 243                 return self.to._meta.pk
 244
 245
 246 class ManyToManyAttribute(ForeignKeyAttribute):
 247         value_class = ManyToManyValue
 248
 249         def validate_value(self, value):
 250                 if not isinstance(value, models.query.QuerySet) or value.model != self.to:
 251                         raise TypeError("The '%s' attribute can only be set to a %s QuerySet." % (self.name, self.to.__name__))
 252
 253         def formfield(self, form_class=forms.ModelMultipleChoiceField, **kwargs):
 254                 return super(ManyToManyAttribute, self).formfield(form_class=form_class, **kwargs)
 255
 256         def value_from_object(self, obj):
 257                 qs = super(ForeignKeyAttribute, self).value_from_object(obj)
 258                 try:
 259                         return qs.values_list('pk', flat=True)
 260                 except:
 261                         return []