models.py 文件源码

def lookup(self, instance=None, content_type=None, selectors=None):
        if instance is not None and content_type is None:
            content_type = ContentType.objects.get_for_model(instance)
        if selectors is None and instance is not None:
            selectors = self._get_selectors(instance, content_type)
        selectors = tuple(selectors)
        if any(s is None for s in selectors):
            return None

        # Look for schema list in cache, keyed by content type and
        # selector list.
        key = schema_cache_key(content_type, selectors)
        cached = caches['jsonattrs'].get(key)
        if cached is not None:
            return cached

        # Not in cache: build schema list using increasing selector
        # sequences.
        base_schemas = self.filter(content_type=content_type)
        schemas = []
        for i in range(len(selectors) + 1):
            schemas += list(base_schemas.filter(selectors=selectors[:i]))
        caches['jsonattrs'].set(key, schemas)
        return schemas