Python SDK and Android SDK have different start_at filtering methods

[ETsagkaris]

I am using Firebase for a project of mine. In Android I can do a query like this:

mDatabase.child(dbRoot).child("Order").orderByChild("user_id").startAt(user.getUid(), "the order id to start from").endAt(user.getUid()).limitToFirst(15)

In "Order" object, I keep all orders made from all users. The Query gives a user's orders with pagination (it brings them in groups of 15). The problem is that in Python SDK the start_at function doesn't support the second input of starting node, and there is no way to make a similar query as far as I can tell

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[hiranya911]

I'm not sure if the underlying REST API supports that style of queries: https://firebase.google.com/docs/database/rest/retrieve-data

@yuchenshi do you know?

[ETsagkaris]

Note that the given Query works exactly as explained in Android SDK, and I hope for Python SDK to make it work as also

[ETsagkaris]

I tried to reverse engineer the code and stumbled upon the spec params that each SDK sends to decide how to filter the data.
Android spec:
{ "vf":"l", "i":"user_id", "sn":"-MMHKiXeYhzZVSc-ryDP","ep":"OiesWhnrJqaiX7ScUoMDvpE8aSq2","l":1,"sp":"OiesWhnrJqaiX7ScUoMDvpE8aSq2"}

Python spec:
{'endAt': '"OiesWhnrJqaiX7ScUoMDvpE8aSq2"', 'limitToFirst': 1, 'orderBy': '"user_id"', 'startAt': '"OiesWhnrJqaiX7ScUoMDvpE8aSq2"'}

It seems like both SDKs use the same pattern, where
sp = startAt
ep = endAt
i = orderBy
l = limitToFirst

What seems to do the trick is the "sn" parameter, which is missing in Python SDK

[yuchenshi]

@hiranya911 I don't work on RTDB any more, but I've got some help from @puf who figured it out:

Basically you can pass the starting node in startAt using the format "value","key", like https://stackoverflow.firebaseio.com/64961237.json?orderBy="vendor"&startAt="a","1"

In Python code, that is: params["startAt"] = valueAsJson + ',"' + key + '"'. Hope that helps.

[ETsagkaris]

Yep seems to be working just fine. I monkey patched it in any case someone has the same issue as me.

def custom_start_at(self, start, key=None):
    if start is None:
        raise ValueError('Start value must not be None.')
    if key != None:
        self._params['startAt'] = json.dumps(start) + ',"' + key + '"'
    else:
        self._params['startAt'] = json.dumps(start)
    return self

db.Query.start_at = custom_start_at

[yuchenshi]

@ETsagkaris Would you consider opening a PR against this repository with your patch? That would help more folks in need and you may be able to remove the monkey-patch in the long run.