WIP: Fix member count inaccurate in Guilds and Parties

[Zamoca42]

Fixes #12286

Changes

Hi there! I've been working on this issue, continuing from the work done in #14203.

Based on the previously implemented content, I've implemented a transaction-based approach.
In addition, I've added error messages for situations that may occur if the transaction fails.

Questions

I have a couple of questions about the implementation.

1. Regarding error handling, I've extended InternalServerError to create DatabaseError and TransactionError. I'm wondering if this is the right approach.

2. For testing purposes, I'm trying to reproduce this issue locally.
   Do you have any suggestions on how to set up a group for a test account without triggering group plan payments? I'm not quite sure how to navigate this.

Any guidance you can provide on these questions would be really helpful. Thanks!

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UUID: 02dac320-60bd-4178-8154-11bc222d4419

[Zamoca42]

Suggested change

	const session = await mongoose.startSession();
	try {
	await session.withTransaction(async () => {
	await member.save({ session });
	await group.save({ session });
	}, {
	retryWrites: true,
	});
	} catch (err) {
	if (err.name === 'MongoError') {
	throw err.hasErrorLabel('TransactionTooLargeForCache')
	? new TransactionError(`Transaction too large for cache: ${err.message}`)
	: new DatabaseError(`Database error: ${err.message}`);
	} else if (err.name === 'ValidationError') {
	throw validationErrors;
	} else {
	throw new InternalServerError(`Unexpected error: ${err.message}`);
	}
	} finally {
	session.endSession();
	}
	const originalMemberCount = group.memberCount;
	try {
	await Group.db.transaction(async session => {
	group.memberCount -= 1;
	await member.save({ session });
	await group.save({ session });
	}, {
	retryWrites: true,
	});
	} catch (err) {
	group.memberCount = originalMemberCount;
	await group.save();
	if (err.name === 'MongoError') {
	throw err.hasErrorLabel('TransactionTooLargeForCache')
	? new TransactionError(`Transaction too large for cache: ${err.message}`)
	: new DatabaseError(`Database error: ${err.message}`);
	} else if (err.name === 'ValidationError') {
	throw validationErrors;
	} else {
	throw new InternalServerError(`Unexpected error: ${err.message}`);
	}
	}

When not import Mongoose with startSession, we could also consider an approach like this.