Generate lines that define many to many relations for this instance.

def get_many_to_many_lines(self, force=False):
        """ Generate lines that define many to many relations for this instance. """

        lines = []

        for field, rel_items in self.many_to_many_waiting_list.items():
            for rel_item in list(rel_items):
                try:
                    pk_name = rel_item._meta.pk.name
                    key = '%s_%s' % (rel_item.__class__.__name__, getattr(rel_item, pk_name))
                    value = "%s" % self.context[key]
                    lines.append('%s.%s.add(%s)' % (self.variable_name, field.name, value))
                    self.many_to_many_waiting_list[field].remove(rel_item)
                except KeyError:
                    if force:
                        item_locator = orm_item_locator(rel_item)
                        self.context["__extra_imports"][rel_item._meta.object_name] = rel_item.__module__
                        lines.append('%s.%s.add( %s )' % (self.variable_name, field.name, item_locator))
                        self.many_to_many_waiting_list[field].remove(rel_item)

        if lines:
            lines.append("")

        return lines