Added the small changes necessary to make creating custom model fields easier.

Also includes some tests for this.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@6651 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/__init__.py

@@ -7,6 +7,7 @@ from django.db.models.query import Q
 from django.db.models.manager import Manager
 from django.db.models.base import Model, AdminOptions
 from django.db.models.fields import *
+from django.db.models.fields.subclassing import SubfieldBase
 from django.db.models.fields.related import ForeignKey, OneToOneField, ManyToManyField, ManyToOneRel, ManyToManyRel, OneToOneRel, TABULAR, STACKED
 from django.db.models import signals
 from django.utils.functional import curry

django/db/models/fields/__init__.py

@@ -147,6 +147,8 @@ class Field(object):
         # exactly which wacky database column type you want to use.
         data_types = get_creation_module().DATA_TYPES
         internal_type = self.get_internal_type()
+        if internal_type not in data_types:
+            return None
         return data_types[internal_type] % self.__dict__
 
     def validate_full(self, field_data, all_data):

django/db/models/fields/subclassing.py

@@ -0,0 +1,53 @@
+"""
+Convenience routines for creating non-trivial Field subclasses.
+
+Add SubfieldBase as the __metaclass__ for your Field subclass, implement
+to_python() and the other necessary methods and everything will work seamlessly.
+"""
+
+from django.utils.maxlength import LegacyMaxlength
+
+class SubfieldBase(LegacyMaxlength):
+    """
+    A metaclass for custom Field subclasses. This ensures the model's attribute
+    has the descriptor protocol attached to it.
+    """
+    def __new__(cls, base, name, attrs):
+        new_class = super(SubfieldBase, cls).__new__(cls, base, name, attrs)
+        new_class.contribute_to_class = make_contrib(
+                attrs.get('contribute_to_class'))
+        return new_class
+
+class Creator(object):
+    """
+    A placeholder class that provides a way to set the attribute on the model.
+    """
+    def __init__(self, field):
+        self.field = field
+
+    def __get__(self, obj, type=None):
+        if obj is None:
+            raise AttributeError('Can only be accessed via an instance.')
+        return self.value
+
+    def __set__(self, obj, value):
+        self.value = self.field.to_python(value)
+
+def make_contrib(func=None):
+    """
+    Returns a suitable contribute_to_class() method for the Field subclass.
+
+    If 'func' is passed in, it is the existing contribute_to_class() method on
+    the subclass and it is called before anything else. It is assumed in this
+    case that the existing contribute_to_class() calls all the necessary
+    superclass methods.
+    """
+    def contribute_to_class(self, cls, name):
+        if func:
+            func(self, cls, name)
+        else:
+            super(self.__class__, self).contribute_to_class(cls, name)
+        setattr(cls, self.name, Creator(self))
+
+    return contribute_to_class
+

tests/modeltests/field_subclassing/models.py

@@ -0,0 +1,106 @@
+"""
+Tests for field subclassing.
+"""
+
+from django.db import models
+from django.utils.encoding import force_unicode
+from django.core import serializers
+
+class Small(object):
+    """
+    A simple class to show that non-trivial Python objects can be used as
+    attributes.
+    """
+    def __init__(self, first, second):
+        self.first, self.second = first, second
+
+    def __unicode__(self):
+        return u'%s%s' % (force_unicode(self.first), force_unicode(self.second))
+
+    def __str__(self):
+        return unicode(self).encode('utf-8')
+
+class SmallField(models.Field):
+    """
+    Turns the "Small" class into a Django field. Because of the similarities
+    with normal character fields and the fact that Small.__unicode__ does
+    something sensible, we don't need to implement a lot here.
+    """
+    __metaclass__ = models.SubfieldBase
+
+    def __init__(self, *args, **kwargs):
+        kwargs['max_length'] = 2
+        super(SmallField, self).__init__(*args, **kwargs)
+
+    def get_internal_type(self):
+        return 'CharField'
+
+    def to_python(self, value):
+        if isinstance(value, Small):
+            return value
+        return Small(value[0], value[1])
+
+    def get_db_prep_save(self, value):
+        return unicode(value)
+
+    def get_db_prep_lookup(self, lookup_type, value):
+        if lookup_type == 'exact':
+            return force_unicode(value)
+        if lookup_type == 'in':
+            return [force_unicode(v) for v in value]
+        if lookup_type == 'isnull':
+            return []
+        raise TypeError('Invalid lookup type: %r' % lookup_type)
+
+    def flatten_data(self, follow, obj=None):
+        return {self.attname: force_unicode(self._get_val_from_obj(obj))}
+
+class MyModel(models.Model):
+    name = models.CharField(max_length=10)
+    data = SmallField('small field')
+
+    def __unicode__(self):
+        return force_unicode(self.name)
+
+__test__ = {'API_TESTS': ur"""
+# Creating a model with custom fields is done as per normal.
+>>> s = Small(1, 2)
+>>> print s
+12
+>>> m = MyModel(name='m', data=s)
+>>> m.save()
+
+# Custom fields still have normal field's attributes.
+>>> m._meta.get_field('data').verbose_name
+'small field'
+
+# The m.data attribute has been initialised correctly. It's a Small object.
+>>> m.data.first, m.data.second
+(1, 2)
+
+# The data loads back from the database correctly and 'data' has the right type.
+>>> m1 = MyModel.objects.get(pk=m.pk)
+>>> isinstance(m1.data, Small)
+True
+>>> print m1.data
+12
+
+# We can do normal filtering on the custom field (and will get an error when we
+# use a lookup type that does not make sense).
+>>> s1 = Small(1, 3)
+>>> s2 = Small('a', 'b')
+>>> MyModel.objects.filter(data__in=[s, s1, s2])
+[<MyModel: m>]
+>>> MyModel.objects.filter(data__lt=s)
+Traceback (most recent call last):
+...
+TypeError: Invalid lookup type: 'lt'
+
+# Serialization works, too.
+>>> stream = serializers.serialize("json", MyModel.objects.all())
+>>> stream
+'[{"pk": 1, "model": "field_subclassing.mymodel", "fields": {"data": "12", "name": "m"}}]'
+>>> obj = list(serializers.deserialize("json", stream))[0]
+>>> obj.object == m
+True
+"""}