Python django.db.models 模块，ManyToManyField() 实例源码

def _check_raw_id_fields_item(self, obj, model, field_name, label):
        """ Check an item of `raw_id_fields`, i.e. check that field named
        `field_name` exists in model `model` and is a ForeignKey or a
        ManyToManyField. """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E002')
        else:
            if not isinstance(field, (models.ForeignKey, models.ManyToManyField)):
                return must_be('a ForeignKey or ManyToManyField',
                               option=label, obj=obj, id='admin.E003')
            else:
                return []

def get_field_style(self, attrs, db_field, style, **kwargs):
        if style == 'm2m_transfer' and isinstance(db_field, ManyToManyField):
            return {'widget': widgets.SelectMultipleTransfer(db_field.verbose_name, False), 'help_text': ''}
        if style == 'm2m_dropdown' and isinstance(db_field, ManyToManyField):
            return {'widget': widgets.SelectMultipleDropdown, 'help_text': ''}
        if style == 'm2m_select' and isinstance(db_field, ManyToManyField):
            return {'widget': widgets.AdminSelectMultiple}

        if style == 'm2m_raw' and isinstance(db_field, ManyToManyField):
            db = kwargs.get('using')
            return {'widget': widgets.ManyToManyRawIdWidget(db_field.rel, self.admin_view, using=db), 'help_text': ''}
        if style == 'm2m_ajax' and isinstance(db_field, ManyToManyField):
            return {'widget': widgets.SelectMultipleAjax(db_field.rel, self.admin_view,False), 'help_text': ''}
        if style == 'm2m_ajax_multi' and isinstance(db_field, ManyToManyField):
            return {'widget': widgets.SelectMultipleAjax(db_field.rel, self.admin_view,True), 'help_text': ''}
        if style == 'm2m_select2' and isinstance(db_field, ManyToManyField):
            return {'widget': widgets.SelectMultipleDropselect, 'help_text': ''}
        return attrs

def _check_ignored_options(self, **kwargs):
        warnings = []

        if self.has_null_arg:
            warnings.append(
                checks.Warning(
                    'null has no effect on ManyToManyField.',
                    hint=None,
                    obj=self,
                    id='fields.W340',
                )
            )

        if len(self._validators) > 0:
            warnings.append(
                checks.Warning(
                    'ManyToManyField does not support validators.',
                    hint=None,
                    obj=self,
                    id='fields.W341',
                )
            )

        return warnings

def contribute_to_class(self, cls, name, **kwargs):
        # To support multiple relations to self, it's useful to have a non-None
        # related name on symmetrical relations for internal reasons. The
        # concept doesn't make a lot of sense externally ("you want me to
        # specify *what* on my non-reversible relation?!"), so we set it up
        # automatically. The funky name reduces the chance of an accidental
        # clash.
        if self.remote_field.symmetrical and (
                self.remote_field.model == "self" or self.remote_field.model == cls._meta.object_name):
            self.remote_field.related_name = "%s_rel_+" % name
        elif self.remote_field.is_hidden():
            # If the backwards relation is disabled, replace the original
            # related_name with one generated from the m2m field name. Django
            # still uses backwards relations internally and we need to avoid
            # clashes between multiple m2m fields with related_name == '+'.
            self.remote_field.related_name = "_%s_%s_+" % (cls.__name__.lower(), name)

        super(ManyToManyField, self).contribute_to_class(cls, name, **kwargs)

        # The intermediate m2m model is not auto created if:
        #  1) There is a manually specified intermediate, or
        #  2) The class owning the m2m field is abstract.
        #  3) The class owning the m2m field has been swapped out.
        if not cls._meta.abstract:
            if self.remote_field.through:
                def resolve_through_model(_, model, field):
                    field.remote_field.through = model
                lazy_related_operation(resolve_through_model, cls, self.remote_field.through, field=self)
            elif not cls._meta.swapped:
                self.remote_field.through = create_many_to_many_intermediary_model(self, cls)

        # Add the descriptor for the m2m relation.
        setattr(cls, self.name, ManyToManyDescriptor(self.remote_field, reverse=False))

        # Set up the accessor for the m2m table name for the relation.
        self.m2m_db_table = curry(self._get_m2m_db_table, cls._meta)

def _check_raw_id_fields_item(self, obj, model, field_name, label):
        """ Check an item of `raw_id_fields`, i.e. check that field named
        `field_name` exists in model `model` and is a ForeignKey or a
        ManyToManyField. """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E002')
        else:
            if not field.many_to_many and not isinstance(field, models.ForeignKey):
                return must_be('a foreign key or a many-to-many field',
                               option=label, obj=obj, id='admin.E003')
            else:
                return []

def _check_prepopulated_fields_key(self, obj, model, field_name, label):
        """ Check a key of `prepopulated_fields` dictionary, i.e. check that it
        is a name of existing field and the field is one of the allowed types.
        """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E027')
        else:
            if isinstance(field, (models.DateTimeField, models.ForeignKey, models.ManyToManyField)):
                return [
                    checks.Error(
                        "The value of '%s' refers to '%s', which must not be a DateTimeField, "
                        "a ForeignKey, or a ManyToManyField." % (label, field_name),
                        obj=obj.__class__,
                        id='admin.E028',
                    )
                ]
            else:
                return []

def _check_raw_id_fields_item(self, obj, model, field_name, label):
        """ Check an item of `raw_id_fields`, i.e. check that field named
        `field_name` exists in model `model` and is a ForeignKey or a
        ManyToManyField. """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E002')
        else:
            if not field.many_to_many and not isinstance(field, models.ForeignKey):
                return must_be('a foreign key or a many-to-many field',
                               option=label, obj=obj, id='admin.E003')
            else:
                return []

def _check_prepopulated_fields_key(self, obj, model, field_name, label):
        """ Check a key of `prepopulated_fields` dictionary, i.e. check that it
        is a name of existing field and the field is one of the allowed types.
        """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E027')
        else:
            if isinstance(field, (models.DateTimeField, models.ForeignKey, models.ManyToManyField)):
                return [
                    checks.Error(
                        "The value of '%s' refers to '%s', which must not be a DateTimeField, "
                        "a ForeignKey, a OneToOneField, or a ManyToManyField." % (label, field_name),
                        obj=obj.__class__,
                        id='admin.E028',
                    )
                ]
            else:
                return []

def _check_raw_id_fields_item(self, obj, model, field_name, label):
        """ Check an item of `raw_id_fields`, i.e. check that field named
        `field_name` exists in model `model` and is a ForeignKey or a
        ManyToManyField. """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E002')
        else:
            if not field.many_to_many and not isinstance(field, models.ForeignKey):
                return must_be('a foreign key or a many-to-many field',
                               option=label, obj=obj, id='admin.E003')
            else:
                return []

def _check_prepopulated_fields_key(self, obj, model, field_name, label):
        """ Check a key of `prepopulated_fields` dictionary, i.e. check that it
        is a name of existing field and the field is one of the allowed types.
        """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E027')
        else:
            if isinstance(field, (models.DateTimeField, models.ForeignKey, models.ManyToManyField)):
                return [
                    checks.Error(
                        "The value of '%s' refers to '%s', which must not be a DateTimeField, "
                        "a ForeignKey, or a ManyToManyField." % (label, field_name),
                        obj=obj.__class__,
                        id='admin.E028',
                    )
                ]
            else:
                return []

def validate_prepopulated_fields(self, cls, model):
        " Validate that prepopulated_fields if a dictionary  containing allowed field types. "
        # prepopulated_fields
        if hasattr(cls, 'prepopulated_fields'):
            check_isdict(cls, 'prepopulated_fields', cls.prepopulated_fields)
            for field, val in cls.prepopulated_fields.items():
                f = get_field(cls, model, 'prepopulated_fields', field)
                if isinstance(f, (models.DateTimeField, models.ForeignKey,
                        models.ManyToManyField)):
                    raise ImproperlyConfigured("'%s.prepopulated_fields['%s']' "
                            "is either a DateTimeField, ForeignKey or "
                            "ManyToManyField. This isn't allowed."
                            % (cls.__name__, field))
                check_isseq(cls, "prepopulated_fields['%s']" % field, val)
                for idx, f in enumerate(val):
                    get_field(cls, model, "prepopulated_fields['%s'][%d]" % (field, idx), f)

def validate_list_display(self, cls, model):
        " Validate that list_display only contains fields or usable attributes. "
        if hasattr(cls, 'list_display'):
            check_isseq(cls, 'list_display', cls.list_display)
            for idx, field in enumerate(cls.list_display):
                if not callable(field):
                    if not hasattr(cls, field):
                        if not hasattr(model, field):
                            try:
                                model._meta.get_field(field)
                            except FieldDoesNotExist:
                                raise ImproperlyConfigured(
                                    "%s.list_display[%d], %r is not a callable or "
                                    "an attribute of %r or found in the model %r."
                                    % (cls.__name__, idx, field, cls.__name__, model._meta.object_name)
                                )
                        else:
                            # getattr(model, field) could be an X_RelatedObjectsDescriptor
                            f = fetch_attr(cls, model, "list_display[%d]" % idx, field)
                            if isinstance(f, models.ManyToManyField):
                                raise ImproperlyConfigured(
                                    "'%s.list_display[%d]', '%s' is a ManyToManyField "
                                    "which is not supported."
                                    % (cls.__name__, idx, field)
                                )

def _check_raw_id_fields_item(self, cls, model, field_name, label):
        """ Check an item of `raw_id_fields`, i.e. check that field named
        `field_name` exists in model `model` and is a ForeignKey or a
        ManyToManyField. """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=cls, id='admin.E002')
        else:
            if not isinstance(field, (models.ForeignKey, models.ManyToManyField)):
                return must_be('a ForeignKey or ManyToManyField',
                               option=label, obj=cls, id='admin.E003')
            else:
                return []

def get_field_docs(self, fieldname):
        try:
            field = self.model._meta.get_field(fieldname)
            if isinstance(field, models.ForeignKey):
                return _serializers[field.rel.to].docs()
            elif isinstance(field, models.ManyToManyField):
                spec = _serializers[field.rel.to].docs()
                spec['array'] = True
                return spec
            elif isinstance(field, models.ManyToOneRel):
                spec = _serializers[field.related_model].docs()
                spec['array'] = True
                return spec
            return FieldDocs(self.model, field)
        except models.FieldDoesNotExist:
            model = getattr(self.model, fieldname).related.related_model
            spec = _serializers[model].docs()
            spec['array'] = True
            return spec

def _check_raw_id_fields_item(self, obj, model, field_name, label):
        """ Check an item of `raw_id_fields`, i.e. check that field named
        `field_name` exists in model `model` and is a ForeignKey or a
        ManyToManyField. """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E002')
        else:
            if not isinstance(field, (models.ForeignKey, models.ManyToManyField)):
                return must_be('a ForeignKey or ManyToManyField',
                               option=label, obj=obj, id='admin.E003')
            else:
                return []

def _check_raw_id_fields_item(self, obj, model, field_name, label):
        """ Check an item of `raw_id_fields`, i.e. check that field named
        `field_name` exists in model `model` and is a ForeignKey or a
        ManyToManyField. """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E002')
        else:
            if not isinstance(field, (models.ForeignKey, models.ManyToManyField)):
                return must_be('a ForeignKey or ManyToManyField',
                               option=label, obj=obj, id='admin.E003')
            else:
                return []

def validate_prepopulated_fields(self, cls, model):
        " Validate that prepopulated_fields if a dictionary  containing allowed field types. "
        # prepopulated_fields
        if hasattr(cls, 'prepopulated_fields'):
            check_isdict(cls, 'prepopulated_fields', cls.prepopulated_fields)
            for field, val in cls.prepopulated_fields.items():
                f = get_field(cls, model, 'prepopulated_fields', field)
                if isinstance(f, (models.DateTimeField, models.ForeignKey,
                        models.ManyToManyField)):
                    raise ImproperlyConfigured("'%s.prepopulated_fields['%s']' "
                            "is either a DateTimeField, ForeignKey or "
                            "ManyToManyField. This isn't allowed."
                            % (cls.__name__, field))
                check_isseq(cls, "prepopulated_fields['%s']" % field, val)
                for idx, f in enumerate(val):
                    get_field(cls, model, "prepopulated_fields['%s'][%d]" % (field, idx), f)

def validate_list_display(self, cls, model):
        " Validate that list_display only contains fields or usable attributes. "
        if hasattr(cls, 'list_display'):
            check_isseq(cls, 'list_display', cls.list_display)
            for idx, field in enumerate(cls.list_display):
                if not callable(field):
                    if not hasattr(cls, field):
                        if not hasattr(model, field):
                            try:
                                model._meta.get_field(field)
                            except FieldDoesNotExist:
                                raise ImproperlyConfigured(
                                    "%s.list_display[%d], %r is not a callable or "
                                    "an attribute of %r or found in the model %r."
                                    % (cls.__name__, idx, field, cls.__name__, model._meta.object_name)
                                )
                        else:
                            # getattr(model, field) could be an X_RelatedObjectsDescriptor
                            f = fetch_attr(cls, model, "list_display[%d]" % idx, field)
                            if isinstance(f, models.ManyToManyField):
                                raise ImproperlyConfigured(
                                    "'%s.list_display[%d]', '%s' is a ManyToManyField "
                                    "which is not supported."
                                    % (cls.__name__, idx, field)
                                )

def _check_raw_id_fields_item(self, cls, model, field_name, label):
        """ Check an item of `raw_id_fields`, i.e. check that field named
        `field_name` exists in model `model` and is a ForeignKey or a
        ManyToManyField. """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=cls, id='admin.E002')
        else:
            if not isinstance(field, (models.ForeignKey, models.ManyToManyField)):
                return must_be('a ForeignKey or ManyToManyField',
                               option=label, obj=cls, id='admin.E003')
            else:
                return []

def accessible_courses(self):
        # If the user has access to a 'parent object', i.e. the related
        # semester, then we grant access to all children
        parent_access = Q(semesters__in=self.accessible_semesters())

        # Also includes courses where the contributor is part of the contributors ManyToManyField,
        # which the user is added to if he/she created the course
        earlier_contributor = Q(contributors__in=[self])
        access_criterion = parent_access | earlier_contributor

        # If the user has recently taken the course, according to dataporten,
        # we grant access. Here, recently means either the current semester,
        # or the last one
        if isinstance(self.user, DataportenUser):
            recent_course = Q(course_code__in=self.user.dataporten.courses.less_semesters_ago(than=2))
            access_criterion = access_criterion | recent_course

        return Course.objects.filter(access_criterion).distinct()

def validate_prepopulated_fields(self, cls, model):
        " Validate that prepopulated_fields if a dictionary  containing allowed field types. "
        # prepopulated_fields
        if hasattr(cls, 'prepopulated_fields'):
            check_isdict(cls, 'prepopulated_fields', cls.prepopulated_fields)
            for field, val in cls.prepopulated_fields.items():
                f = get_field(cls, model, 'prepopulated_fields', field)
                if isinstance(f, (models.DateTimeField, models.ForeignKey,
                        models.ManyToManyField)):
                    raise ImproperlyConfigured("'%s.prepopulated_fields['%s']' "
                            "is either a DateTimeField, ForeignKey or "
                            "ManyToManyField. This isn't allowed."
                            % (cls.__name__, field))
                check_isseq(cls, "prepopulated_fields['%s']" % field, val)
                for idx, f in enumerate(val):
                    get_field(cls, model, "prepopulated_fields['%s'][%d]" % (field, idx), f)

def validate_list_display(self, cls, model):
        " Validate that list_display only contains fields or usable attributes. "
        if hasattr(cls, 'list_display'):
            check_isseq(cls, 'list_display', cls.list_display)
            for idx, field in enumerate(cls.list_display):
                if not callable(field):
                    if not hasattr(cls, field):
                        if not hasattr(model, field):
                            try:
                                model._meta.get_field(field)
                            except FieldDoesNotExist:
                                raise ImproperlyConfigured(
                                    "%s.list_display[%d], %r is not a callable or "
                                    "an attribute of %r or found in the model %r."
                                    % (cls.__name__, idx, field, cls.__name__, model._meta.object_name)
                                )
                        else:
                            # getattr(model, field) could be an X_RelatedObjectsDescriptor
                            f = fetch_attr(cls, model, "list_display[%d]" % idx, field)
                            if isinstance(f, models.ManyToManyField):
                                raise ImproperlyConfigured(
                                    "'%s.list_display[%d]', '%s' is a ManyToManyField "
                                    "which is not supported."
                                    % (cls.__name__, idx, field)
                                )

def _check_raw_id_fields_item(self, cls, model, field_name, label):
        """ Check an item of `raw_id_fields`, i.e. check that field named
        `field_name` exists in model `model` and is a ForeignKey or a
        ManyToManyField. """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=cls, id='admin.E002')
        else:
            if not isinstance(field, (models.ForeignKey, models.ManyToManyField)):
                return must_be('a ForeignKey or ManyToManyField',
                               option=label, obj=cls, id='admin.E003')
            else:
                return []

def get_form_datas(self):
        """
        ? Request ??? Form ??????
        """
        if self.request_method == 'get':
            initial = dict(self.request.GET.items())
            for k in initial:
                try:
                    f = self.opts.get_field(k)
                except models.FieldDoesNotExist:
                    continue
                if isinstance(f, models.ManyToManyField):
                    # ?????????????????
                    initial[k] = initial[k].split(",")
            return {'initial': initial}
        else:
            return {'data': self.request.POST, 'files': self.request.FILES}

def _check_raw_id_fields_item(self, obj, model, field_name, label):
        """ Check an item of `raw_id_fields`, i.e. check that field named
        `field_name` exists in model `model` and is a ForeignKey or a
        ManyToManyField. """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E002')
        else:
            if not field.many_to_many and not isinstance(field, models.ForeignKey):
                return must_be('a foreign key or a many-to-many field',
                               option=label, obj=obj, id='admin.E003')
            else:
                return []

def _check_prepopulated_fields_key(self, obj, model, field_name, label):
        """ Check a key of `prepopulated_fields` dictionary, i.e. check that it
        is a name of existing field and the field is one of the allowed types.
        """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E027')
        else:
            if isinstance(field, (models.DateTimeField, models.ForeignKey, models.ManyToManyField)):
                return [
                    checks.Error(
                        "The value of '%s' refers to '%s', which must not be a DateTimeField, "
                        "a ForeignKey, or a ManyToManyField." % (label, field_name),
                        obj=obj.__class__,
                        id='admin.E028',
                    )
                ]
            else:
                return []

def _check_raw_id_fields_item(self, obj, model, field_name, label):
        """ Check an item of `raw_id_fields`, i.e. check that field named
        `field_name` exists in model `model` and is a ForeignKey or a
        ManyToManyField. """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E002')
        else:
            if not field.many_to_many and not isinstance(field, models.ForeignKey):
                return must_be('a foreign key or a many-to-many field',
                               option=label, obj=obj, id='admin.E003')
            else:
                return []

def _check_prepopulated_fields_key(self, obj, model, field_name, label):
        """ Check a key of `prepopulated_fields` dictionary, i.e. check that it
        is a name of existing field and the field is one of the allowed types.
        """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E027')
        else:
            if isinstance(field, (models.DateTimeField, models.ForeignKey, models.ManyToManyField)):
                return [
                    checks.Error(
                        "The value of '%s' refers to '%s', which must not be a DateTimeField, "
                        "a ForeignKey, or a ManyToManyField." % (label, field_name),
                        obj=obj.__class__,
                        id='admin.E028',
                    )
                ]
            else:
                return []

def _check_raw_id_fields_item(self, obj, model, field_name, label):
        """ Check an item of `raw_id_fields`, i.e. check that field named
        `field_name` exists in model `model` and is a ForeignKey or a
        ManyToManyField. """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E002')
        else:
            if not field.many_to_many and not isinstance(field, models.ForeignKey):
                return must_be('a foreign key or a many-to-many field',
                               option=label, obj=obj, id='admin.E003')
            else:
                return []

def _check_prepopulated_fields_key(self, obj, model, field_name, label):
        """ Check a key of `prepopulated_fields` dictionary, i.e. check that it
        is a name of existing field and the field is one of the allowed types.
        """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E027')
        else:
            if isinstance(field, (models.DateTimeField, models.ForeignKey, models.ManyToManyField)):
                return [
                    checks.Error(
                        "The value of '%s' refers to '%s', which must not be a DateTimeField, "
                        "a ForeignKey, or a ManyToManyField." % (label, field_name),
                        obj=obj.__class__,
                        id='admin.E028',
                    )
                ]
            else:
                return []

def _check_raw_id_fields_item(self, obj, model, field_name, label):
        """ Check an item of `raw_id_fields`, i.e. check that field named
        `field_name` exists in model `model` and is a ForeignKey or a
        ManyToManyField. """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E002')
        else:
            if not field.many_to_many and not isinstance(field, models.ForeignKey):
                return must_be('a foreign key or a many-to-many field',
                               option=label, obj=obj, id='admin.E003')
            else:
                return []

def _check_prepopulated_fields_key(self, obj, model, field_name, label):
        """ Check a key of `prepopulated_fields` dictionary, i.e. check that it
        is a name of existing field and the field is one of the allowed types.
        """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E027')
        else:
            if isinstance(field, (models.DateTimeField, models.ForeignKey, models.ManyToManyField)):
                return [
                    checks.Error(
                        "The value of '%s' refers to '%s', which must not be a DateTimeField, "
                        "a ForeignKey, or a ManyToManyField." % (label, field_name),
                        obj=obj.__class__,
                        id='admin.E028',
                    )
                ]
            else:
                return []

def _showfields_get_content(self, field_name, field_type=type(None)):
        "helper for __unicode__"
        content = getattr(self, field_name)
        if self.polymorphic_showfield_old_format:
            out = ': '
        else:
            out = ' '
        if issubclass(field_type, models.ForeignKey):
            if content is None:
                out += 'None'
            else:
                out += content.__class__.__name__
        elif issubclass(field_type, models.ManyToManyField):
            out += '%d' % content.count()
        elif isinstance(content, six.integer_types):
            out += str(content)
        elif content is None:
            out += 'None'
        else:
            txt = str(content)
            if len(txt) > self.polymorphic_showfield_max_field_width:
                txt = txt[:self.polymorphic_showfield_max_field_width - 2] + '..'
            out += '"' + txt + '"'
        return out

def _is_m2m(user_field):
    field = FeatureFlipper._meta.get_field(user_field)
    return isinstance(field, ManyToManyField)

def __enter__(self):
        self._old_au_local_m2m = AbstractUser._meta.local_many_to_many
        self._old_pm_local_m2m = PermissionsMixin._meta.local_many_to_many
        groups = models.ManyToManyField(Group, blank=True)
        groups.contribute_to_class(PermissionsMixin, "groups")
        user_permissions = models.ManyToManyField(Permission, blank=True)
        user_permissions.contribute_to_class(PermissionsMixin, "user_permissions")
        PermissionsMixin._meta.local_many_to_many = [groups, user_permissions]
        AbstractUser._meta.local_many_to_many = [groups, user_permissions]

def _check_field_name(self):
        field_name = self._get_field_name()
        try:
            field = self.model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return [
                checks.Error(
                    "CurrentSiteManager could not find a field named '%s'." % field_name,
                    hint=None,
                    obj=self,
                    id='sites.E001',
                )
            ]

        if not isinstance(field, (models.ForeignKey, models.ManyToManyField)):
            return [
                checks.Error(
                    "CurrentSiteManager cannot use '%s.%s' as it is not a ForeignKey or ManyToManyField." % (
                        self.model._meta.object_name, field_name
                    ),
                    hint=None,
                    obj=self,
                    id='sites.E002',
                )
            ]

        return []

def _check_field_spec_item(self, obj, model, field_name, label):
        if field_name in obj.readonly_fields:
            # Stuff can be put in fields that isn't actually a model field if
            # it's in readonly_fields, readonly_fields will handle the
            # validation of such things.
            return []
        else:
            try:
                field = model._meta.get_field(field_name)
            except FieldDoesNotExist:
                # If we can't find a field on the model that matches, it could
                # be an extra field on the form.
                return []
            else:
                if (isinstance(field, models.ManyToManyField) and
                        not field.remote_field.through._meta.auto_created):
                    return [
                        checks.Error(
                            ("The value of '%s' cannot include the ManyToManyField '%s', "
                             "because that field manually specifies a relationship model.")
                            % (label, field_name),
                            hint=None,
                            obj=obj.__class__,
                            id='admin.E013',
                        )
                    ]
                else:
                    return []

def _check_filter_item(self, obj, model, field_name, label):
        """ Check one item of `filter_vertical` or `filter_horizontal`, i.e.
        check that given field exists and is a ManyToManyField. """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E019')
        else:
            if not isinstance(field, models.ManyToManyField):
                return must_be('a ManyToManyField', option=label, obj=obj, id='admin.E020')
            else:
                return []

def formfield_for_manytomany(self, db_field, request=None, **kwargs):
        """
        Get a form Field for a ManyToManyField.
        """
        # If it uses an intermediary model that isn't auto created, don't show
        # a field in admin.
        if not db_field.remote_field.through._meta.auto_created:
            return None
        db = kwargs.get('using')

        if db_field.name in self.raw_id_fields:
            kwargs['widget'] = widgets.ManyToManyRawIdWidget(db_field.remote_field,
                                    self.admin_site, using=db)
            kwargs['help_text'] = ''
        elif db_field.name in (list(self.filter_vertical) + list(self.filter_horizontal)):
            kwargs['widget'] = widgets.FilteredSelectMultiple(
                db_field.verbose_name,
                db_field.name in self.filter_vertical
            )

        if 'queryset' not in kwargs:
            queryset = self.get_field_queryset(db, db_field, request)
            if queryset is not None:
                kwargs['queryset'] = queryset

        form_field = db_field.formfield(**kwargs)
        if isinstance(form_field.widget, SelectMultiple) and not isinstance(form_field.widget, CheckboxSelectMultiple):
            msg = _('Hold down "Control", or "Command" on a Mac, to select more than one.')
            help_text = form_field.help_text
            form_field.help_text = string_concat(help_text, ' ', msg) if help_text else msg
        return form_field

def get_changeform_initial_data(self, request):
        """
        Get the initial form data.
        Unless overridden, this populates from the GET params.
        """
        initial = dict(request.GET.items())
        for k in initial:
            try:
                f = self.model._meta.get_field(k)
            except FieldDoesNotExist:
                continue
            # We have to special-case M2Ms as a list of comma-separated PKs.
            if isinstance(f, models.ManyToManyField):
                initial[k] = initial[k].split(",")
        return initial

def _generate_added_field(self, app_label, model_name, field_name):
        field = self.new_apps.get_model(app_label, model_name)._meta.get_field(field_name)
        # Fields that are foreignkeys/m2ms depend on stuff
        dependencies = []
        if field.remote_field and field.remote_field.model:
            # Account for FKs to swappable models
            swappable_setting = getattr(field, 'swappable_setting', None)
            if swappable_setting is not None:
                dep_app_label = "__setting__"
                dep_object_name = swappable_setting
            else:
                dep_app_label = field.remote_field.model._meta.app_label
                dep_object_name = field.remote_field.model._meta.object_name
            dependencies = [(dep_app_label, dep_object_name, None, True)]
            if getattr(field.remote_field, "through", None) and not field.remote_field.through._meta.auto_created:
                dependencies.append((
                    field.remote_field.through._meta.app_label,
                    field.remote_field.through._meta.object_name,
                    None,
                    True,
                ))
        # You can't just add NOT NULL fields with no default or fields
        # which don't allow empty strings as default.
        preserve_default = True
        if (not field.null and not field.has_default() and
                not isinstance(field, models.ManyToManyField) and
                not (field.blank and field.empty_strings_allowed)):
            field = field.clone()
            field.default = self.questioner.ask_not_null_addition(field_name, model_name)
            preserve_default = False
        self.add_operation(
            app_label,
            operations.AddField(
                model_name=model_name,
                name=field_name,
                field=field,
                preserve_default=preserve_default,
            ),
            dependencies=dependencies,
        )

def __init__(self, to, related_name=None, related_query_name=None,
            limit_choices_to=None, symmetrical=None, through=None,
            through_fields=None, db_constraint=True, db_table=None,
            swappable=True, **kwargs):
        try:
            to._meta
        except AttributeError:
            assert isinstance(to, six.string_types), (
                "%s(%r) is invalid. First parameter to ManyToManyField must be "
                "either a model, a model name, or the string %r" %
                (self.__class__.__name__, to, RECURSIVE_RELATIONSHIP_CONSTANT)
            )
            # Class names must be ASCII in Python 2.x, so we forcibly coerce it
            # here to break early if there's a problem.
            to = str(to)

        if symmetrical is None:
            symmetrical = (to == RECURSIVE_RELATIONSHIP_CONSTANT)

        if through is not None:
            assert db_table is None, (
                "Cannot specify a db_table if an intermediary model is used."
            )

        kwargs['rel'] = self.rel_class(
            self, to,
            related_name=related_name,
            related_query_name=related_query_name,
            limit_choices_to=limit_choices_to,
            symmetrical=symmetrical,
            through=through,
            through_fields=through_fields,
            db_constraint=db_constraint,
        )
        self.has_null_arg = 'null' in kwargs

        super(ManyToManyField, self).__init__(**kwargs)

        self.db_table = db_table
        self.swappable = swappable

def check(self, **kwargs):
        errors = super(ManyToManyField, self).check(**kwargs)
        errors.extend(self._check_unique(**kwargs))
        errors.extend(self._check_relationship_model(**kwargs))
        errors.extend(self._check_ignored_options(**kwargs))
        return errors

def db_type(self, connection):
        # A ManyToManyField is not represented by a single column,
        # so return None.
        return None

def _check_field_spec_item(self, obj, model, field_name, label):
        if field_name in obj.readonly_fields:
            # Stuff can be put in fields that isn't actually a model field if
            # it's in readonly_fields, readonly_fields will handle the
            # validation of such things.
            return []
        else:
            try:
                field = model._meta.get_field(field_name)
            except FieldDoesNotExist:
                # If we can't find a field on the model that matches, it could
                # be an extra field on the form.
                return []
            else:
                if (isinstance(field, models.ManyToManyField) and
                        not field.remote_field.through._meta.auto_created):
                    return [
                        checks.Error(
                            "The value of '%s' cannot include the ManyToManyField '%s', "
                            "because that field manually specifies a relationship model."
                            % (label, field_name),
                            obj=obj.__class__,
                            id='admin.E013',
                        )
                    ]
                else:
                    return []

def _check_filter_item(self, obj, model, field_name, label):
        """ Check one item of `filter_vertical` or `filter_horizontal`, i.e.
        check that given field exists and is a ManyToManyField. """

        try:
            field = model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label,
                                          model=model, obj=obj, id='admin.E019')
        else:
            if not field.many_to_many:
                return must_be('a many-to-many field', option=label, obj=obj, id='admin.E020')
            else:
                return []

def formfield_for_manytomany(self, db_field, request, **kwargs):
        """
        Get a form Field for a ManyToManyField.
        """
        # If it uses an intermediary model that isn't auto created, don't show
        # a field in admin.
        if not db_field.remote_field.through._meta.auto_created:
            return None
        db = kwargs.get('using')

        if db_field.name in self.raw_id_fields:
            kwargs['widget'] = widgets.ManyToManyRawIdWidget(db_field.remote_field, self.admin_site, using=db)
        elif db_field.name in (list(self.filter_vertical) + list(self.filter_horizontal)):
            kwargs['widget'] = widgets.FilteredSelectMultiple(
                db_field.verbose_name,
                db_field.name in self.filter_vertical
            )

        if 'queryset' not in kwargs:
            queryset = self.get_field_queryset(db, db_field, request)
            if queryset is not None:
                kwargs['queryset'] = queryset

        form_field = db_field.formfield(**kwargs)
        if isinstance(form_field.widget, SelectMultiple) and not isinstance(form_field.widget, CheckboxSelectMultiple):
            msg = _('Hold down "Control", or "Command" on a Mac, to select more than one.')
            help_text = form_field.help_text
            form_field.help_text = string_concat(help_text, ' ', msg) if help_text else msg
        return form_field

def get_changeform_initial_data(self, request):
        """
        Get the initial form data.
        Unless overridden, this populates from the GET params.
        """
        initial = dict(request.GET.items())
        for k in initial:
            try:
                f = self.model._meta.get_field(k)
            except FieldDoesNotExist:
                continue
            # We have to special-case M2Ms as a list of comma-separated PKs.
            if isinstance(f, models.ManyToManyField):
                initial[k] = initial[k].split(",")
        return initial

def formfield_for_dbfield(self, db_field, **kwargs):
        # If it uses an intermediary model that isn't auto created, don't show
        # a field in admin.
        if isinstance(db_field, models.ManyToManyField) and not db_field.rel.through._meta.auto_created:
            return None

        attrs = self.get_field_attrs(db_field, **kwargs)
        return db_field.formfield(**dict(attrs, **kwargs))

def get_field_style(self, db_field, style, **kwargs):
        if style in ('radio', 'radio-inline') and (db_field.choices or isinstance(db_field, models.ForeignKey)):
            attrs = {'widget': widgets.AdminRadioSelect(
                attrs={'inline': 'inline' if style == 'radio-inline' else ''})}
            if db_field.choices:
                attrs['choices'] = db_field.get_choices(
                    include_blank=db_field.blank,
                    blank_choice=[('', _('Null'))]
                )
            return attrs

        if style in ('checkbox', 'checkbox-inline') and isinstance(db_field, models.ManyToManyField):
            return {'widget': widgets.AdminCheckboxSelect(attrs={'inline': style == 'checkbox-inline'}),
                    'help_text': None}