覆盖GAE db.Model python 2.7上的__setattr__

Question

GAE db.Model无法存储元组列表。因此，当我将列表拉回实体时，我需要将列表保存为json.dumps字符串并将json.loads字符串保存。我想自动化这个。这是我的尝试：

class example(db.Model):
    someAttr = db.StringListProperty()
    A = db.StringProperty()
    B = db.StringProperty()
    C = db.StringProperty()

    def __setattr__(self, name, value):
        #convert json to string for storage
        if name in ("A", "B", "C"):
            value = json.dumps(value)
        #call default set method
        return super(Quote, self).__setattr__(name, value)

    def __getattribute__(self, name):
        #convert string to json for retrieval
        if name in ("A", "B", "C"):
            val = super(Quote, self).__getattribute__(name)
            return json.loads(val)
        else: 
            # default get behavior
            return super(Quote, self).__getattribute__(name)

当我尝试设置实体的A，B，C属性时：

BadValueError: Property C must be a str or unicode instance, not a list

Answer 1

如果您不需要存储非常大的JSON，我建议您查看NDB。它内置了JsonProperty：https://developers.google.com/appengine/docs/python/ndb/properties#types。

我还在App Engine Googl Group中发现了一篇有趣的文章，讨论了一种更有效的存储大型JSON的方法：https://groups.google.com/forum/#!msg/google-appengine/WPfAvHDGNjQ/XfakEMm1qzoJ