SQLAlchemy session with Celery (Multipart batch writes)

Question

Supposing I have a mobile app which will send a filled form data (which also contains images) to a Commercial software using its API, and this data should be committed all at once.

Since the mobile does not have enough memory to send all the dataset at once, I need to send it as a Multipart batch.

I use transactions in cases where I want to perform a bunch of operations on the database, but I kind of need them to be performed all at once, meaning that I don't want the database to change out from under me while I'm in the middle of making my changes. And if I'm making a bunch of changes, I don't want users to be able to read my set of documents in that partially changed state. And I certainly don't want a set of operations failing halfway through, leaving me in a weird and inconsistent state forever. It's got to be all or nothing.

I know that Firebase provides the batch write operation which does exactly what I need. However, I need to do this into a local database (like redis or postgres).

The first approach I considered is using POST requests identified by a main session_ID.

 - POST /session -> returns new SESSION_ID
 - POST [image1] /session/<session_id> -> returns new IMG_ID
 - POST [image2] /session/<session_id> -> returns new IMG_ID
 - PUT /session/<session_id> -> validate/update metadata

However it does not seem very robust to handle errors.

The second approach I was considering is combining SQLAlchemy session with Celery task using Flask or FastAPI. I am not sure if it is common to do this to solve this issue. I just found this question. I would like to know what do you guys recommend for this second case approach (sending all data parts first, and commit all at once) ?