contrib/cowell/fields.py

   1 """
   2 The Attributes defined in this file can be assigned as fields on a proxy of
   3 a 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                 class Meta:
  19                         proxy = True
  20 """
  21 from django import forms
  22 from django.core.exceptions import FieldError
  23 from django.db import models
  24 from django.db.models.fields import NOT_PROVIDED
  25 from django.utils.text import capfirst
  26 from philo.signals import entity_class_prepared
  27 from philo.models import ManyToManyValue, JSONValue, ForeignKeyValue, Attribute, Entity
  28
  29
  30 __all__ = ('JSONAttribute', 'ForeignKeyAttribute', 'ManyToManyAttribute')
  31
  32
  33 ATTRIBUTE_REGISTRY = '_attribute_registry'
  34
  35
  36 class EntityProxyField(object):
  37         def __init__(self, verbose_name=None, help_text=None, default=NOT_PROVIDED, editable=True, *args, **kwargs):
  38                 self.verbose_name = verbose_name
  39                 self.help_text = help_text
  40                 self.default = default
  41                 self.editable = editable
  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 has_default(self):
  73                 return self.default is not NOT_PROVIDED
  74
  75
  76 class AttributeFieldDescriptor(object):
  77         def __init__(self, field):
  78                 self.field = field
  79
  80         def get_registry(self, instance):
  81                 if ATTRIBUTE_REGISTRY not in instance.__dict__:
  82                         instance.__dict__[ATTRIBUTE_REGISTRY] = {'added': set(), 'removed': set()}
  83                 return instance.__dict__[ATTRIBUTE_REGISTRY]
  84
  85         def __get__(self, instance, owner):
  86                 if instance is None:
  87                         return self
  88
  89                 if self.field.name not in instance.__dict__:
  90                         instance.__dict__[self.field.name] = instance.attributes.get(self.field.attribute_key, None)
  91
  92                 return instance.__dict__[self.field.name]
  93
  94         def __set__(self, instance, value):
  95                 if instance is None:
  96                         raise AttributeError("%s must be accessed via instance" % self.field.name)
  97
  98                 self.field.validate_value(value)
  99                 instance.__dict__[self.field.name] = value
 100
 101                 registry = self.get_registry(instance)
 102                 registry['added'].add(self.field)
 103                 registry['removed'].discard(self.field)
 104
 105         def __delete__(self, instance):
 106                 del instance.__dict__[self.field.name]
 107
 108                 registry = self.get_registry(instance)
 109                 registry['added'].discard(self.field)
 110                 registry['removed'].add(self.field)
 111
 112
 113 def process_attribute_fields(sender, instance, created, **kwargs):
 114         if ATTRIBUTE_REGISTRY in instance.__dict__:
 115                 registry = instance.__dict__[ATTRIBUTE_REGISTRY]
 116                 instance.attribute_set.filter(key__in=[field.attribute_key for field in registry['removed']]).delete()
 117
 118                 for field in registry['added']:
 119                         try:
 120                                 attribute = instance.attribute_set.get(key=field.attribute_key)
 121                         except Attribute.DoesNotExist:
 122                                 attribute = Attribute()
 123                                 attribute.entity = instance
 124                                 attribute.key = field.attribute_key
 125
 126                         value_class = field.value_class
 127                         if isinstance(attribute.value, value_class):
 128                                 value = attribute.value
 129                         else:
 130                                 if isinstance(attribute.value, models.Model):
 131                                         attribute.value.delete()
 132                                 value = value_class()
 133
 134                         value.set_value(getattr(instance, field.name, None))
 135                         value.save()
 136
 137                         attribute.value = value
 138                         attribute.save()
 139                 del instance.__dict__[ATTRIBUTE_REGISTRY]
 140
 141
 142 class AttributeField(EntityProxyField):
 143         def __init__(self, attribute_key=None, **kwargs):
 144                 self.attribute_key = attribute_key
 145                 super(AttributeField, self).__init__(**kwargs)
 146
 147         def actually_contribute_to_class(self, sender, **kwargs):
 148                 super(AttributeField, self).actually_contribute_to_class(sender, **kwargs)
 149                 setattr(sender, self.name, AttributeFieldDescriptor(self))
 150                 opts = sender._entity_meta
 151                 if not hasattr(opts, '_has_attribute_fields'):
 152                         opts._has_attribute_fields = True
 153                         models.signals.post_save.connect(process_attribute_fields, sender=sender)
 154
 155
 156         def contribute_to_class(self, cls, name):
 157                 if self.attribute_key is None:
 158                         self.attribute_key = name
 159                 super(AttributeField, self).contribute_to_class(cls, name)
 160
 161         def validate_value(self, value):
 162                 "Confirm that the value is valid or raise an appropriate error."
 163                 raise NotImplementedError("validate_value must be implemented by AttributeField subclasses.")
 164
 165         @property
 166         def value_class(self):
 167                 raise AttributeError("value_class must be defined on AttributeField subclasses.")
 168
 169
 170 class JSONAttribute(AttributeField):
 171         value_class = JSONValue
 172
 173         def __init__(self, field_template=None, **kwargs):
 174                 super(JSONAttribute, self).__init__(**kwargs)
 175                 if field_template is None:
 176                         field_template = models.CharField(max_length=255)
 177                 self.field_template = field_template
 178
 179         def validate_value(self, value):
 180                 pass
 181
 182         def formfield(self, **kwargs):
 183                 defaults = {
 184                         'required': False,
 185                         'label': capfirst(self.verbose_name),
 186                         'help_text': self.help_text
 187                 }
 188                 if self.has_default():
 189                         defaults['initial'] = self.default
 190                 defaults.update(kwargs)
 191                 return self.field_template.formfield(**defaults)
 192
 193
 194 class ForeignKeyAttribute(AttributeField):
 195         value_class = ForeignKeyValue
 196
 197         def __init__(self, model, limit_choices_to=None, **kwargs):
 198                 super(ForeignKeyAttribute, self).__init__(**kwargs)
 199                 self.model = model
 200                 if limit_choices_to is None:
 201                         limit_choices_to = {}
 202                 self.limit_choices_to = limit_choices_to
 203
 204         def validate_value(self, value):
 205                 if value is not None and not isinstance(value, self.model) :
 206                         raise TypeError("The '%s' attribute can only be set to an instance of %s or None." % (self.name, self.model.__name__))
 207
 208         def formfield(self, form_class=forms.ModelChoiceField, **kwargs):
 209                 defaults = {
 210                         'queryset': self.model._default_manager.complex_filter(self.limit_choices_to)
 211                 }
 212                 defaults.update(kwargs)
 213                 return super(ForeignKeyAttribute, self).formfield(form_class=form_class, **defaults)
 214
 215         def value_from_object(self, obj):
 216                 relobj = super(ForeignKeyAttribute, self).value_from_object(obj)
 217                 return getattr(relobj, 'pk', None)
 218
 219
 220 class ManyToManyAttribute(ForeignKeyAttribute):
 221         value_class = ManyToManyValue
 222
 223         def validate_value(self, value):
 224                 if not isinstance(value, models.query.QuerySet) or value.model != self.model:
 225                         raise TypeError("The '%s' attribute can only be set to a %s QuerySet." % (self.name, self.model.__name__))
 226
 227         def formfield(self, form_class=forms.ModelMultipleChoiceField, **kwargs):
 228                 return super(ManyToManyAttribute, self).formfield(form_class=form_class, **kwargs)
 229
 230         def value_from_object(self, obj):
 231                 qs = super(ForeignKeyAttribute, self).value_from_object(obj)
 232                 try:
 233                         return qs.values_list('pk', flat=True)
 234                 except:
 235                         return []