def save(self, force_insert=False, force_update=False, using=None):
        """
        Saves the current instance. Override this in a subclass if you want to
        control the saving process.

        The 'force_insert' and 'force_update' parameters can be used to insist
        that the "save" must be an SQL insert or update (or equivalent for
        non-SQL backends), respectively. Normally, they should not be set.
        """
        if force_insert and force_update:
            raise ValueError("Cannot force both insert and updating in model saving.")
        self.save_base(using=using, force_insert=force_insert, force_update=force_update)

    save.alters_data = True

    def save_base(self, raw=False, cls=None, origin=None, force_insert=False,
            force_update=False, using=None):
        """
        Does the heavy-lifting involved in saving. Subclasses shouldn't need to
        override this method. It's separate from save() in order to hide the
        need for overrides of save() to pass around internal-only parameters
        ('raw', 'cls', and 'origin').
        """
        using = using or router.db_for_write(self.__class__, instance=self)
        connection = connections[using]
        assert not (force_insert and force_update)
        if cls is None:
            cls = self.__class__
            meta = cls._meta
            if not meta.proxy:
                origin = cls
        else:
            meta = cls._meta

        if origin and not meta.auto_created:
            signals.pre_save.send(sender=origin, instance=self, raw=raw, using=using)

        # If we are in a raw save, save the object exactly as presented.
        # That means that we don't try to be smart about saving attributes
        # that might have come from the parent class - we just save the
        # attributes we have been given to the class we have been given.
        # We also go through this process to defer the save of proxy objects
        # to their actual underlying model.
        if not raw or meta.proxy:
            if meta.proxy:
                org = cls
            else:
                org = None
            for parent, field in meta.parents.items():
                # At this point, parent's primary key field may be unknown
                # (for example, from administration form which doesn't fill
                # this field). If so, fill it.
                if field and getattr(self, parent._meta.pk.attname) is None and getattr(self, field.attname) is not None:
                    setattr(self, parent._meta.pk.attname, getattr(self, field.attname))

                self.save_base(cls=parent, origin=org, using=using)

                if field:
                    setattr(self, field.attname, self._get_pk_val(parent._meta))
            if meta.proxy:
                return

        if not meta.proxy:
            non_pks = [f for f in meta.local_fields if not f.primary_key]

            # First, try an UPDATE. If that doesn't update anything, do an INSERT.
            pk_val = self._get_pk_val(meta)
            pk_set = pk_val is not None
            record_exists = True
            manager = cls._base_manager
            if pk_set:
                # Determine whether a record with the primary key already exists.
                if (force_update or (not force_insert and
                        manager.using(using).filter(pk=pk_val).exists())):
                    # It does already exist, so do an UPDATE.
                    if force_update or non_pks:
                        values = [(f, None, (raw and getattr(self, f.attname) or f.pre_save(self, False))) for f in non_pks]
                        rows = manager.using(using).filter(pk=pk_val)._update(values)
                        if force_update and not rows:
                            raise DatabaseError("Forced update did not affect any rows.")
                else:
                    record_exists = False
            if not pk_set or not record_exists:
                if meta.order_with_respect_to:
                    # If this is a model with an order_with_respect_to
                    # autopopulate the _order field
                    field = meta.order_with_respect_to
                    order_value = manager.using(using).filter(**{field.name: getattr(self, field.attname)}).count()
                    self._order = order_value

                if not pk_set:
                    if force_update:
                        raise ValueError("Cannot force an update in save() with no primary key.")
                    values = [(f, f.get_db_prep_save(raw and getattr(self, f.attname) or f.pre_save(self, True), connection=connection))
                        for f in meta.local_fields if not isinstance(f, AutoField)]
                else:
                    values = [(f, f.get_db_prep_save(raw and getattr(self, f.attname) or f.pre_save(self, True), connection=connection))
                        for f in meta.local_fields]

                record_exists = False

                update_pk = bool(meta.has_auto_field and not pk_set)
                if values:
                    # Create a new record.
                    result = manager._insert(values, return_id=update_pk, using=using)
                else:
                    # Create a new record with defaults for everything.
                    result = manager._insert([(meta.pk, connection.ops.pk_default_value())], return_id=update_pk, raw_values=True, using=using)

                if update_pk:
                    setattr(self, meta.pk.attname, result)
            transaction.commit_unless_managed(using=using)

        # Store the database on which the object was saved
        self._state.db = using
        # Once saved, this is no longer a to-be-added instance.
        self._state.adding = False

        # Signal that the save is complete
        if origin and not meta.auto_created:
            signals.post_save.send(sender=origin, instance=self,
                created=(not record_exists), raw=raw, using=using)