models/fields.py

   1 from django.db import models
   2 from django.db.models import signals
   3 from django.core.exceptions import FieldError
   4 from philo.models.base import Entity
   5
   6
   7 __all__ = ('AttributeField', 'RelationshipField')
   8
   9
  10 class AttributeFieldDescriptor(object):
  11         def __init__(self, field):
  12                 self.field = field
  13
  14         def __get__(self, instance, owner):
  15                 if instance:
  16                         if self.field.key in instance._added_attribute_registry:
  17                                 return instance._added_attribute_registry[self.field.key]
  18                         if self.field.key in instance._removed_attribute_registry:
  19                                 return None
  20                         try:
  21                                 return instance.attributes[self.field.key]
  22                         except KeyError:
  23                                 return None
  24                 else:
  25                         raise AttributeError('The \'%s\' attribute can only be accessed from %s instances.' % (self.field.name, owner.__name__))
  26
  27         def __set__(self, instance, value):
  28                 if self.field.key in instance._removed_attribute_registry:
  29                         instance._removed_attribute_registry.remove(self.field.key)
  30                 instance._added_attribute_registry[self.field.key] = value
  31
  32         def __delete__(self, instance):
  33                 if self.field.key in instance._added_attribute_registry:
  34                         del instance._added_attribute_registry[self.field.key]
  35                 instance._removed_attribute_registry.append(self.field.key)
  36
  37
  38 class AttributeField(object):
  39         def __init__(self, key):
  40                 self.key = key
  41
  42         def actually_contribute_to_class(self, sender, **kwargs):
  43                 setattr(sender, self.name, AttributeFieldDescriptor(self))
  44
  45         def contribute_to_class(self, cls, name):
  46                 if issubclass(cls, Entity):
  47                         self.name = name
  48                         signals.class_prepared.connect(self.actually_contribute_to_class, sender=cls)
  49                 else:
  50                         raise FieldError('AttributeFields can only be declared on Entity subclasses.')
  51
  52
  53 class RelationshipFieldDescriptor(object):
  54         def __init__(self, field):
  55                 self.field = field
  56
  57         def __get__(self, instance, owner):
  58                 if instance:
  59                         if self.field.key in instance._added_relationship_registry:
  60                                 return instance._added_relationship_registry[self.field.key]
  61                         if self.field.key in instance._removed_relationship_registry:
  62                                 return None
  63                         try:
  64                                 return instance.relationships[self.field.key]
  65                         except KeyError:
  66                                 return None
  67                 else:
  68                         raise AttributeError('The \'%s\' attribute can only be accessed from %s instances.' % (self.field.name, owner.__name__))
  69
  70         def __set__(self, instance, value):
  71                 if isinstance(value, (models.Model, type(None))):
  72                         if self.field.key in instance._removed_relationship_registry:
  73                                 instance._removed_relationship_registry.remove(self.field.key)
  74                         instance._added_relationship_registry[self.field.key] = value
  75                 else:
  76                         raise AttributeError('The \'%s\' attribute can only be set using existing Model objects.' % self.field.name)
  77
  78         def __delete__(self, instance):
  79                 if self.field.key in instance._added_relationship_registry:
  80                         del instance._added_relationship_registry[self.field.key]
  81                 instance._removed_relationship_registry.append(self.field.key)
  82
  83
  84 class RelationshipField(object):
  85         def __init__(self, key):
  86                 self.key = key
  87
  88         def actually_contribute_to_class(self, sender, **kwargs):
  89                 setattr(sender, self.name, RelationshipFieldDescriptor(self))
  90
  91         def contribute_to_class(self, cls, name):
  92                 if issubclass(cls, Entity):
  93                         self.name = name
  94                         signals.class_prepared.connect(self.actually_contribute_to_class, sender=cls)
  95                 else:
  96                         raise FieldError('RelationshipFields can only be declared on Entity subclasses.')