diff -r 6641e941ef1e -r ff1a9aa48cfd app/django/forms/models.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/app/django/forms/models.py	Tue Oct 14 16:00:59 2008 +0000
@@ -0,0 +1,698 @@
+"""
+Helper functions for creating Form classes from Django models
+and database field objects.
+"""
+
+from django.utils.encoding import smart_unicode
+from django.utils.datastructures import SortedDict
+from django.utils.text import get_text_list, capfirst
+from django.utils.translation import ugettext_lazy as _
+
+from util import ValidationError, ErrorList
+from forms import BaseForm, get_declared_fields
+from fields import Field, ChoiceField, IntegerField, EMPTY_VALUES
+from widgets import Select, SelectMultiple, HiddenInput, MultipleHiddenInput
+from widgets import media_property
+from formsets import BaseFormSet, formset_factory, DELETION_FIELD_NAME
+
+try:
+    set
+except NameError:
+    from sets import Set as set     # Python 2.3 fallback
+
+__all__ = (
+    'ModelForm', 'BaseModelForm', 'model_to_dict', 'fields_for_model',
+    'save_instance', 'form_for_fields', 'ModelChoiceField',
+    'ModelMultipleChoiceField',
+)
+
+
+def save_instance(form, instance, fields=None, fail_message='saved',
+                  commit=True, exclude=None):
+    """
+    Saves bound Form ``form``'s cleaned_data into model instance ``instance``.
+
+    If commit=True, then the changes to ``instance`` will be saved to the
+    database. Returns ``instance``.
+    """
+    from django.db import models
+    opts = instance._meta
+    if form.errors:
+        raise ValueError("The %s could not be %s because the data didn't"
+                         " validate." % (opts.object_name, fail_message))
+    cleaned_data = form.cleaned_data
+    for f in opts.fields:
+        if not f.editable or isinstance(f, models.AutoField) \
+                or not f.name in cleaned_data:
+            continue
+        if fields and f.name not in fields:
+            continue
+        if exclude and f.name in exclude:
+            continue
+        f.save_form_data(instance, cleaned_data[f.name])
+    # Wrap up the saving of m2m data as a function.
+    def save_m2m():
+        opts = instance._meta
+        cleaned_data = form.cleaned_data
+        for f in opts.many_to_many:
+            if fields and f.name not in fields:
+                continue
+            if f.name in cleaned_data:
+                f.save_form_data(instance, cleaned_data[f.name])
+    if commit:
+        # If we are committing, save the instance and the m2m data immediately.
+        instance.save()
+        save_m2m()
+    else:
+        # We're not committing. Add a method to the form to allow deferred
+        # saving of m2m data.
+        form.save_m2m = save_m2m
+    return instance
+
+def make_model_save(model, fields, fail_message):
+    """Returns the save() method for a Form."""
+    def save(self, commit=True):
+        return save_instance(self, model(), fields, fail_message, commit)
+    return save
+
+def make_instance_save(instance, fields, fail_message):
+    """Returns the save() method for a Form."""
+    def save(self, commit=True):
+        return save_instance(self, instance, fields, fail_message, commit)
+    return save
+
+def form_for_fields(field_list):
+    """
+    Returns a Form class for the given list of Django database field instances.
+    """
+    fields = SortedDict([(f.name, f.formfield())
+                         for f in field_list if f.editable])
+    return type('FormForFields', (BaseForm,), {'base_fields': fields})
+
+
+# ModelForms #################################################################
+
+def model_to_dict(instance, fields=None, exclude=None):
+    """
+    Returns a dict containing the data in ``instance`` suitable for passing as
+    a Form's ``initial`` keyword argument.
+
+    ``fields`` is an optional list of field names. If provided, only the named
+    fields will be included in the returned dict.
+
+    ``exclude`` is an optional list of field names. If provided, the named
+    fields will be excluded from the returned dict, even if they are listed in
+    the ``fields`` argument.
+    """
+    # avoid a circular import
+    from django.db.models.fields.related import ManyToManyField, OneToOneField
+    opts = instance._meta
+    data = {}
+    for f in opts.fields + opts.many_to_many:
+        if not f.editable:
+            continue
+        if fields and not f.name in fields:
+            continue
+        if exclude and f.name in exclude:
+            continue
+        if isinstance(f, ManyToManyField):
+            # If the object doesn't have a primry key yet, just use an empty
+            # list for its m2m fields. Calling f.value_from_object will raise
+            # an exception.
+            if instance.pk is None:
+                data[f.name] = []
+            else:
+                # MultipleChoiceWidget needs a list of pks, not object instances.
+                data[f.name] = [obj.pk for obj in f.value_from_object(instance)]
+        else:
+            data[f.name] = f.value_from_object(instance)
+    return data
+
+def fields_for_model(model, fields=None, exclude=None, formfield_callback=lambda f: f.formfield()):
+    """
+    Returns a ``SortedDict`` containing form fields for the given model.
+
+    ``fields`` is an optional list of field names. If provided, only the named
+    fields will be included in the returned fields.
+
+    ``exclude`` is an optional list of field names. If provided, the named
+    fields will be excluded from the returned fields, even if they are listed
+    in the ``fields`` argument.
+    """
+    # TODO: if fields is provided, it would be nice to return fields in that order
+    field_list = []
+    opts = model._meta
+    for f in opts.fields + opts.many_to_many:
+        if not f.editable:
+            continue
+        if fields and not f.name in fields:
+            continue
+        if exclude and f.name in exclude:
+            continue
+        formfield = formfield_callback(f)
+        if formfield:
+            field_list.append((f.name, formfield))
+    return SortedDict(field_list)
+
+class ModelFormOptions(object):
+    def __init__(self, options=None):
+        self.model = getattr(options, 'model', None)
+        self.fields = getattr(options, 'fields', None)
+        self.exclude = getattr(options, 'exclude', None)
+
+
+class ModelFormMetaclass(type):
+    def __new__(cls, name, bases, attrs):
+        formfield_callback = attrs.pop('formfield_callback',
+                lambda f: f.formfield())
+        try:
+            parents = [b for b in bases if issubclass(b, ModelForm)]
+        except NameError:
+            # We are defining ModelForm itself.
+            parents = None
+        declared_fields = get_declared_fields(bases, attrs, False)
+        new_class = super(ModelFormMetaclass, cls).__new__(cls, name, bases,
+                attrs)
+        if not parents:
+            return new_class
+
+        if 'media' not in attrs:
+            new_class.media = media_property(new_class)
+        opts = new_class._meta = ModelFormOptions(getattr(new_class, 'Meta', None))
+        if opts.model:
+            # If a model is defined, extract form fields from it.
+            fields = fields_for_model(opts.model, opts.fields,
+                                      opts.exclude, formfield_callback)
+            # Override default model fields with any custom declared ones
+            # (plus, include all the other declared fields).
+            fields.update(declared_fields)
+        else:
+            fields = declared_fields
+        new_class.declared_fields = declared_fields
+        new_class.base_fields = fields
+        return new_class
+
+class BaseModelForm(BaseForm):
+    def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
+                 initial=None, error_class=ErrorList, label_suffix=':',
+                 empty_permitted=False, instance=None):
+        opts = self._meta
+        if instance is None:
+            # if we didn't get an instance, instantiate a new one
+            self.instance = opts.model()
+            object_data = {}
+        else:
+            self.instance = instance
+            object_data = model_to_dict(instance, opts.fields, opts.exclude)
+        # if initial was provided, it should override the values from instance
+        if initial is not None:
+            object_data.update(initial)
+        super(BaseModelForm, self).__init__(data, files, auto_id, prefix, object_data,
+                                            error_class, label_suffix, empty_permitted)
+    def clean(self):
+        self.validate_unique()
+        return self.cleaned_data
+
+    def validate_unique(self):
+        from django.db.models.fields import FieldDoesNotExist
+
+        # Gather a list of checks to perform. Since this is a ModelForm, some
+        # fields may have been excluded; we can't perform a unique check on a
+        # form that is missing fields involved in that check.
+        unique_checks = []
+        for check in self.instance._meta.unique_together[:]:
+            fields_on_form = [field for field in check if field in self.fields]
+            if len(fields_on_form) == len(check):
+                unique_checks.append(check)
+
+        form_errors = []
+
+        # Gather a list of checks for fields declared as unique and add them to
+        # the list of checks. Again, skip fields not on the form.
+        for name, field in self.fields.items():
+            try:
+                f = self.instance._meta.get_field_by_name(name)[0]
+            except FieldDoesNotExist:
+                # This is an extra field that's not on the ModelForm, ignore it
+                continue
+            # MySQL can't handle ... WHERE pk IS NULL, so make sure we
+            # don't generate queries of that form.
+            is_null_pk = f.primary_key and self.cleaned_data[name] is None
+            if name in self.cleaned_data and f.unique and not is_null_pk:
+                unique_checks.append((name,))
+
+        # Don't run unique checks on fields that already have an error.
+        unique_checks = [check for check in unique_checks if not [x in self._errors for x in check if x in self._errors]]
+
+        bad_fields = set()
+        for unique_check in unique_checks:
+            # Try to look up an existing object with the same values as this
+            # object's values for all the unique field.
+
+            lookup_kwargs = {}
+            for field_name in unique_check:
+                lookup_kwargs[field_name] = self.cleaned_data[field_name]
+
+            qs = self.instance.__class__._default_manager.filter(**lookup_kwargs)
+
+            # Exclude the current object from the query if we are editing an
+            # instance (as opposed to creating a new one)
+            if self.instance.pk is not None:
+                qs = qs.exclude(pk=self.instance.pk)
+
+            # This cute trick with extra/values is the most efficient way to
+            # tell if a particular query returns any results.
+            if qs.extra(select={'a': 1}).values('a').order_by():
+                model_name = capfirst(self.instance._meta.verbose_name)
+
+                # A unique field
+                if len(unique_check) == 1:
+                    field_name = unique_check[0]
+                    field_label = self.fields[field_name].label
+                    # Insert the error into the error dict, very sneaky
+                    self._errors[field_name] = ErrorList([
+                        _(u"%(model_name)s with this %(field_label)s already exists.") % \
+                        {'model_name': unicode(model_name),
+                         'field_label': unicode(field_label)}
+                    ])
+                # unique_together
+                else:
+                    field_labels = [self.fields[field_name].label for field_name in unique_check]
+                    field_labels = get_text_list(field_labels, _('and'))
+                    form_errors.append(
+                        _(u"%(model_name)s with this %(field_label)s already exists.") % \
+                        {'model_name': unicode(model_name),
+                         'field_label': unicode(field_labels)}
+                    )
+
+                # Mark these fields as needing to be removed from cleaned data
+                # later.
+                for field_name in unique_check:
+                    bad_fields.add(field_name)
+
+        for field_name in bad_fields:
+            del self.cleaned_data[field_name]
+        if form_errors:
+            # Raise the unique together errors since they are considered
+            # form-wide.
+            raise ValidationError(form_errors)
+
+    def save(self, commit=True):
+        """
+        Saves this ``form``'s cleaned_data into model instance
+        ``self.instance``.
+
+        If commit=True, then the changes to ``instance`` will be saved to the
+        database. Returns ``instance``.
+        """
+        if self.instance.pk is None:
+            fail_message = 'created'
+        else:
+            fail_message = 'changed'
+        return save_instance(self, self.instance, self._meta.fields, fail_message, commit)
+
+class ModelForm(BaseModelForm):
+    __metaclass__ = ModelFormMetaclass
+
+def modelform_factory(model, form=ModelForm, fields=None, exclude=None,
+                       formfield_callback=lambda f: f.formfield()):
+    # HACK: we should be able to construct a ModelForm without creating
+    # and passing in a temporary inner class
+    class Meta:
+        pass
+    setattr(Meta, 'model', model)
+    setattr(Meta, 'fields', fields)
+    setattr(Meta, 'exclude', exclude)
+    class_name = model.__name__ + 'Form'
+    return ModelFormMetaclass(class_name, (form,), {'Meta': Meta,
+                              'formfield_callback': formfield_callback})
+
+
+# ModelFormSets ##############################################################
+
+class BaseModelFormSet(BaseFormSet):
+    """
+    A ``FormSet`` for editing a queryset and/or adding new objects to it.
+    """
+    model = None
+
+    def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
+                 queryset=None, **kwargs):
+        self.queryset = queryset
+        defaults = {'data': data, 'files': files, 'auto_id': auto_id, 'prefix': prefix}
+        defaults['initial'] = [model_to_dict(obj) for obj in self.get_queryset()]
+        defaults.update(kwargs)
+        super(BaseModelFormSet, self).__init__(**defaults)
+
+    def _construct_form(self, i, **kwargs):
+        if i < self._initial_form_count:
+            kwargs['instance'] = self.get_queryset()[i]
+        return super(BaseModelFormSet, self)._construct_form(i, **kwargs)
+
+    def get_queryset(self):
+        if not hasattr(self, '_queryset'):
+            if self.queryset is not None:
+                qs = self.queryset
+            else:
+                qs = self.model._default_manager.get_query_set()
+            if self.max_num > 0:
+                self._queryset = qs[:self.max_num]
+            else:
+                self._queryset = qs
+        return self._queryset
+
+    def save_new(self, form, commit=True):
+        """Saves and returns a new model instance for the given form."""
+        return save_instance(form, self.model(), exclude=[self._pk_field.name], commit=commit)
+
+    def save_existing(self, form, instance, commit=True):
+        """Saves and returns an existing model instance for the given form."""
+        return save_instance(form, instance, exclude=[self._pk_field.name], commit=commit)
+
+    def save(self, commit=True):
+        """Saves model instances for every form, adding and changing instances
+        as necessary, and returns the list of instances.
+        """
+        if not commit:
+            self.saved_forms = []
+            def save_m2m():
+                for form in self.saved_forms:
+                    form.save_m2m()
+            self.save_m2m = save_m2m
+        return self.save_existing_objects(commit) + self.save_new_objects(commit)
+
+    def save_existing_objects(self, commit=True):
+        self.changed_objects = []
+        self.deleted_objects = []
+        if not self.get_queryset():
+            return []
+
+        # Put the objects from self.get_queryset into a dict so they are easy to lookup by pk
+        existing_objects = {}
+        for obj in self.get_queryset():
+            existing_objects[obj.pk] = obj
+        saved_instances = []
+        for form in self.initial_forms:
+            obj = existing_objects[form.cleaned_data[self._pk_field.name]]
+            if self.can_delete and form.cleaned_data[DELETION_FIELD_NAME]:
+                self.deleted_objects.append(obj)
+                obj.delete()
+            else:
+                if form.changed_data:
+                    self.changed_objects.append((obj, form.changed_data))
+                    saved_instances.append(self.save_existing(form, obj, commit=commit))
+                    if not commit:
+                        self.saved_forms.append(form)
+        return saved_instances
+
+    def save_new_objects(self, commit=True):
+        self.new_objects = []
+        for form in self.extra_forms:
+            if not form.has_changed():
+                continue
+            # If someone has marked an add form for deletion, don't save the
+            # object.
+            if self.can_delete and form.cleaned_data[DELETION_FIELD_NAME]:
+                continue
+            self.new_objects.append(self.save_new(form, commit=commit))
+            if not commit:
+                self.saved_forms.append(form)
+        return self.new_objects
+
+    def add_fields(self, form, index):
+        """Add a hidden field for the object's primary key."""
+        from django.db.models import AutoField
+        self._pk_field = pk = self.model._meta.pk
+        if pk.auto_created or isinstance(pk, AutoField):
+            form.fields[self._pk_field.name] = IntegerField(required=False, widget=HiddenInput)
+        super(BaseModelFormSet, self).add_fields(form, index)
+
+def modelformset_factory(model, form=ModelForm, formfield_callback=lambda f: f.formfield(),
+                         formset=BaseModelFormSet,
+                         extra=1, can_delete=False, can_order=False,
+                         max_num=0, fields=None, exclude=None):
+    """
+    Returns a FormSet class for the given Django model class.
+    """
+    form = modelform_factory(model, form=form, fields=fields, exclude=exclude,
+                             formfield_callback=formfield_callback)
+    FormSet = formset_factory(form, formset, extra=extra, max_num=max_num,
+                              can_order=can_order, can_delete=can_delete)
+    FormSet.model = model
+    return FormSet
+
+
+# InlineFormSets #############################################################
+
+class BaseInlineFormSet(BaseModelFormSet):
+    """A formset for child objects related to a parent."""
+    def __init__(self, data=None, files=None, instance=None,
+                 save_as_new=False, prefix=None):
+        from django.db.models.fields.related import RelatedObject
+        self.instance = instance
+        self.save_as_new = save_as_new
+        # is there a better way to get the object descriptor?
+        self.rel_name = RelatedObject(self.fk.rel.to, self.model, self.fk).get_accessor_name()
+        super(BaseInlineFormSet, self).__init__(data, files, prefix=prefix or self.rel_name)
+
+    def _construct_forms(self):
+        if self.save_as_new:
+            self._total_form_count = self._initial_form_count
+            self._initial_form_count = 0
+        super(BaseInlineFormSet, self)._construct_forms()
+
+    def _construct_form(self, i, **kwargs):
+        form = super(BaseInlineFormSet, self)._construct_form(i, **kwargs)
+        if self.save_as_new:
+            # Remove the primary key from the form's data, we are only
+            # creating new instances
+            form.data[form.add_prefix(self._pk_field.name)] = None
+        return form
+
+    def get_queryset(self):
+        """
+        Returns this FormSet's queryset, but restricted to children of
+        self.instance
+        """
+        kwargs = {self.fk.name: self.instance}
+        return self.model._default_manager.filter(**kwargs)
+
+    def save_new(self, form, commit=True):
+        kwargs = {self.fk.get_attname(): self.instance.pk}
+        new_obj = self.model(**kwargs)
+        return save_instance(form, new_obj, exclude=[self._pk_field.name], commit=commit)
+
+    def add_fields(self, form, index):
+        super(BaseInlineFormSet, self).add_fields(form, index)
+        if self._pk_field == self.fk:
+            form.fields[self._pk_field.name] = IntegerField(required=False, widget=HiddenInput)
+
+def _get_foreign_key(parent_model, model, fk_name=None):
+    """
+    Finds and returns the ForeignKey from model to parent if there is one.
+    If fk_name is provided, assume it is the name of the ForeignKey field.
+    """
+    # avoid circular import
+    from django.db.models import ForeignKey
+    opts = model._meta
+    if fk_name:
+        fks_to_parent = [f for f in opts.fields if f.name == fk_name]
+        if len(fks_to_parent) == 1:
+            fk = fks_to_parent[0]
+            if not isinstance(fk, ForeignKey) or \
+                    (fk.rel.to != parent_model and
+                     fk.rel.to not in parent_model._meta.get_parent_list()):
+                raise Exception("fk_name '%s' is not a ForeignKey to %s" % (fk_name, parent_model))
+        elif len(fks_to_parent) == 0:
+            raise Exception("%s has no field named '%s'" % (model, fk_name))
+    else:
+        # Try to discover what the ForeignKey from model to parent_model is
+        fks_to_parent = [
+            f for f in opts.fields
+            if isinstance(f, ForeignKey)
+            and (f.rel.to == parent_model
+                or f.rel.to in parent_model._meta.get_parent_list())
+        ]
+        if len(fks_to_parent) == 1:
+            fk = fks_to_parent[0]
+        elif len(fks_to_parent) == 0:
+            raise Exception("%s has no ForeignKey to %s" % (model, parent_model))
+        else:
+            raise Exception("%s has more than 1 ForeignKey to %s" % (model, parent_model))
+    return fk
+
+
+def inlineformset_factory(parent_model, model, form=ModelForm,
+                          formset=BaseInlineFormSet, fk_name=None,
+                          fields=None, exclude=None,
+                          extra=3, can_order=False, can_delete=True, max_num=0,
+                          formfield_callback=lambda f: f.formfield()):
+    """
+    Returns an ``InlineFormSet`` for the given kwargs.
+
+    You must provide ``fk_name`` if ``model`` has more than one ``ForeignKey``
+    to ``parent_model``.
+    """
+    fk = _get_foreign_key(parent_model, model, fk_name=fk_name)
+    # enforce a max_num=1 when the foreign key to the parent model is unique.
+    if fk.unique:
+        max_num = 1
+    if exclude is not None:
+        exclude = list(exclude)
+        exclude.append(fk.name)
+    else:
+        exclude = [fk.name]
+    kwargs = {
+        'form': form,
+        'formfield_callback': formfield_callback,
+        'formset': formset,
+        'extra': extra,
+        'can_delete': can_delete,
+        'can_order': can_order,
+        'fields': fields,
+        'exclude': exclude,
+        'max_num': max_num,
+    }
+    FormSet = modelformset_factory(model, **kwargs)
+    FormSet.fk = fk
+    return FormSet
+
+
+# Fields #####################################################################
+
+class ModelChoiceIterator(object):
+    def __init__(self, field):
+        self.field = field
+        self.queryset = field.queryset
+
+    def __iter__(self):
+        if self.field.empty_label is not None:
+            yield (u"", self.field.empty_label)
+        if self.field.cache_choices:
+            if self.field.choice_cache is None:
+                self.field.choice_cache = [
+                    self.choice(obj) for obj in self.queryset.all()
+                ]
+            for choice in self.field.choice_cache:
+                yield choice
+        else:
+            for obj in self.queryset.all():
+                yield self.choice(obj)
+
+    def choice(self, obj):
+        if self.field.to_field_name:
+            # FIXME: The try..except shouldn't be necessary here. But this is
+            # going in just before 1.0, so I want to be careful. Will check it
+            # out later.
+            try:
+                key = getattr(obj, self.field.to_field_name).pk
+            except AttributeError:
+                key = getattr(obj, self.field.to_field_name)
+        else:
+            key = obj.pk
+        return (key, self.field.label_from_instance(obj))
+
+
+class ModelChoiceField(ChoiceField):
+    """A ChoiceField whose choices are a model QuerySet."""
+    # This class is a subclass of ChoiceField for purity, but it doesn't
+    # actually use any of ChoiceField's implementation.
+    default_error_messages = {
+        'invalid_choice': _(u'Select a valid choice. That choice is not one of'
+                            u' the available choices.'),
+    }
+
+    def __init__(self, queryset, empty_label=u"---------", cache_choices=False,
+                 required=True, widget=None, label=None, initial=None,
+                 help_text=None, to_field_name=None, *args, **kwargs):
+        self.empty_label = empty_label
+        self.cache_choices = cache_choices
+
+        # Call Field instead of ChoiceField __init__() because we don't need
+        # ChoiceField.__init__().
+        Field.__init__(self, required, widget, label, initial, help_text,
+                       *args, **kwargs)
+        self.queryset = queryset
+        self.choice_cache = None
+        self.to_field_name = to_field_name
+
+    def _get_queryset(self):
+        return self._queryset
+
+    def _set_queryset(self, queryset):
+        self._queryset = queryset
+        self.widget.choices = self.choices
+
+    queryset = property(_get_queryset, _set_queryset)
+
+    # this method will be used to create object labels by the QuerySetIterator.
+    # Override it to customize the label.
+    def label_from_instance(self, obj):
+        """
+        This method is used to convert objects into strings; it's used to
+        generate the labels for the choices presented by this object. Subclasses
+        can override this method to customize the display of the choices.
+        """
+        return smart_unicode(obj)
+
+    def _get_choices(self):
+        # If self._choices is set, then somebody must have manually set
+        # the property self.choices. In this case, just return self._choices.
+        if hasattr(self, '_choices'):
+            return self._choices
+
+        # Otherwise, execute the QuerySet in self.queryset to determine the
+        # choices dynamically. Return a fresh QuerySetIterator that has not been
+        # consumed. Note that we're instantiating a new QuerySetIterator *each*
+        # time _get_choices() is called (and, thus, each time self.choices is
+        # accessed) so that we can ensure the QuerySet has not been consumed. This
+        # construct might look complicated but it allows for lazy evaluation of
+        # the queryset.
+        return ModelChoiceIterator(self)
+
+    choices = property(_get_choices, ChoiceField._set_choices)
+
+    def clean(self, value):
+        Field.clean(self, value)
+        if value in EMPTY_VALUES:
+            return None
+        try:
+            key = self.to_field_name or 'pk'
+            value = self.queryset.get(**{key: value})
+        except self.queryset.model.DoesNotExist:
+            raise ValidationError(self.error_messages['invalid_choice'])
+        return value
+
+class ModelMultipleChoiceField(ModelChoiceField):
+    """A MultipleChoiceField whose choices are a model QuerySet."""
+    widget = SelectMultiple
+    hidden_widget = MultipleHiddenInput
+    default_error_messages = {
+        'list': _(u'Enter a list of values.'),
+        'invalid_choice': _(u'Select a valid choice. %s is not one of the'
+                            u' available choices.'),
+    }
+
+    def __init__(self, queryset, cache_choices=False, required=True,
+                 widget=None, label=None, initial=None,
+                 help_text=None, *args, **kwargs):
+        super(ModelMultipleChoiceField, self).__init__(queryset, None,
+            cache_choices, required, widget, label, initial, help_text,
+            *args, **kwargs)
+
+    def clean(self, value):
+        if self.required and not value:
+            raise ValidationError(self.error_messages['required'])
+        elif not self.required and not value:
+            return []
+        if not isinstance(value, (list, tuple)):
+            raise ValidationError(self.error_messages['list'])
+        final_values = []
+        for val in value:
+            try:
+                obj = self.queryset.get(pk=val)
+            except self.queryset.model.DoesNotExist:
+                raise ValidationError(self.error_messages['invalid_choice'] % val)
+            else:
+                final_values.append(obj)
+        return final_values