Unsubscribe nested subscriptions

[TimoBechtel]

what

Add feature to automatically unsubscribe all nested subscriptions.

why

Currently, unsubscribing nested subscriptions is very verbose and error prone when forgetting to unsubscribe a nested subscribe call.

This is especially annoying when using something like react that needs cleanup.

let cleanupFunctions = [];
const unsubscribeA = db.get("books").each(bookRef => {
  const unsubscribeB = bookRef.get("pages").each(pageRef => {
    const unsubscribeC = pageRef.on(console.log);
    cleanupFunctions.push(unsubscribeC);
  });
  cleanupFunctions.push(unsubscribeB);
});
cleanupFunctions.push(unsubscribeA);

// Cleanup
cleanupFunctions.forEach(fn => fn());
cleanupFunctions = [];

We could make this a lot simpler by allowing to unsubscribe all nested subscriptions:

const unsubscribe = db.get("books").each(bookRef => {
  bookRef.get("pages").each(pageRef => {
    pageRef.on(console.log);
  });
});

// Cleanup 
unsubscribe({ nested: true });

Or we can add a subscriptionContext that automatically unsubscribes every subscription inside the context:

const unsubscribe = db.subscriptionContext(ctx => {
	ctx.get("books").each(bookRef => {
		bookRef.get("pages").each(pageRef => {
			pageRef.on(console.log);
		});
	});
});

This should probably be the default behavior.

We might add a flag to enable this as default behavior until the next major version is released, as this might be a breaking change.