Officially expose MongoDB client

[mtrezza]

New Feature / Enhancement Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.

Current Limitation

Parse Server uses a richer interface to interact with the database than it exposes for developers to use. For example upserting (upsertOneObject), mass-updating by query (updateObjectsByQuery) or findOneAndUpdate. These are currently only accessible via:

• the internal database adapter, for example Parse.Server.database.adapter.findOneAndUpdate
• the higher level Parse.Server.database.update which adds some convenience, like supplying the schema for the target class and transforming high-level Parse references to raw MongoDB references

Given these method's versatility and efficiency, we can assume that they are widely in use. Especially since the Parse Server configuration has been made more accessible with Parse.Server in #7869.

As an example for efficiency consider the case of upserting an object:

• With he public interface an upsert requires 1 unique index, 1 write request, catching the error if the object exists and then 1 update request.
• With the internal interface an upsert requires 1 upsert upsertOneObject request.

However, these methods are all internal. Changing them would not be considered breaking changes and it wouldn't even be in the changelog. It is even suggested that they may be removed if possible:

parse-server/src/Adapters/Storage/Mongo/MongoStorageAdapter.js

Lines 586 to 587 in fe02d3e

	// Hopefully we can get rid of this. It's only used for config and hooks.
	upsertOneObject(

Feature / Enhancement Description

Parse Server should officially expose a method in Cloud Code similar to the Parse.Server.database.update method. Exposing Parse.Server.database.update directly would likely be unpractical, since the method is not well structured in its design and is used internally throughout the code. It could be available in Cloud Code via something like await Parse.Cloud.Database.execute({ ... }).

Availability in the Parse JS SDK is out of scope for this feature, see also #8787.

Example Use Case

• How to use Mongo's findOneAndUpdate. #4258 (comment)

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[mtrezza]

I'm revising my suggestion. After playing around with Parse.Server.database.update and the lower level Parse.Server.database.adapter.findOneAndUpdate I found that their behavior is really weird. They are applying various Parse <-> MongoDB transformations that are really confusing the way they are implemented.

For example, a date value has to be supplied in a different format (JavaScript Date object, Parse JSON with date ISO string) depending on whether it's set in the update object or the query object. In addition it's converted differently whether is the createdAt, updatedAt field, a custom date field or an atomic operator like $setOnInsert. All this also makes contributing to Parse Server difficult and should probably be cleaned up at some point.

I don't think these API should be officially exposed, because:

• It's really difficult to follow the data transformations.
• It's easy to store values as the wrong type in the DB because a wrong data type seems to work for certain operations but then fails for others on the same data.
• It's again limiting developers to the lower level methods Parse Server provides.

So instead I'm suggesting to expose the MongoDB adapter in a more convenient way. It should give total freedom of what command to execute, without any Parse <-> MongoDB transformations. This is in line with the MongoDB aggregation pipeline which also does not (should not) apply any transformations.

[Moumouls]

@mtrezza here a simple "trick" to access the mongo client, may be it should be exposed under a specific method ?

An easy one i guess finally here

export const getMongoClient = async (): Promise<GetMongoClient> => {
	await parseServer.config.databaseController.adapter.connect()
	return {
		db: parseServer.config.databaseController.adapter.database,
		client: parseServer.config.databaseController.adapter.client,
	}
}

[mtrezza]

I was thinking about an officially documented method within the Parse namespace.