Support for Retrieving Model from DocumentSnapshot in Firestore DB Triggers

[elersong]

Description

There is a need to retrieve a model from the DocumentSnapshot provided by Firestore DB triggers. The current solution involves using plainToClass from class-transformer, but a more integrated approach within Fireorm would be beneficial.

Steps to Reproduce

1. Set up a Firestore DB trigger.
2. Attempt to retrieve a model directly from the DocumentSnapshot provided by the trigger.

Expected Behavior

A method within Fireorm that allows easy conversion of DocumentSnapshot to a model, enabling seamless use of Fireorm in Firestore DB triggers.

Actual Behavior

Currently, users need to manually convert the snapshot data to their model using plainToClass.

Acceptance Criteria

• Develop a method (e.g., extractTFromDocSnap(docSnap)) within Fireorm to handle the conversion from DocumentSnapshot to a model.
• Ensure the method works reliably with all fields declared in the model.
• Consider future integration of Fireorm as a middleware in triggers to automatically translate payloads.

Additional Context

• October 18, 2019: Initial inquiry about using Fireorm with Firestore DB triggers.
• October 19, 2019: Suggested use of plainToClass as a temporary solution.
• October 21, 2019: Discussion about exposing an internal function for converting document snapshots to models and the potential for future middleware integration.
• July 3, 2020: Comment about the blocking nature of this issue and offer to help with a solution.
• July 7, 2020: Mentioned in another issue related to using Fireorm with Firebase Client SDK.

Original Issue