Mutations that should cancel each other out (create + immediate delete)?

[christianalares]

Hey all! I'm trying to learn how the cancellation of mutations in the collection works. Currently I get race conditions if a quickly add a record and delete it immediately since the record does not exist in the db yet when trying to delete it. I've read this in the docs:

When multiple mutations operate on the same item within a transaction, TanStack DB intelligently merges them to:

insert + delete | removed | Mutations cancel each other out

However to my understanding in this repro, the insertion and deletion is made in two different transaction, but I cant find the correct way to deal with this?

Here is a repro:
https://github.com/christianalares/tanstack-db-race-condition-repro

[Toba-bonjour]

Those merges only appear within a given transaction, they are not cross-transaction.

The function you are talking about can be seen here:

db/packages/db/src/transactions.ts

Lines 24 to 42 in 5eb8300

	/**
	* Merges two pending mutations for the same item within a transaction
	*
	* Merge behavior truth table:
	* - (insert, update) → insert (merge changes, keep empty original)
	* - (insert, delete) → null (cancel both mutations)
	* - (update, delete) → delete (delete dominates)
	* - (update, update) → update (replace with latest, union changes)
	* - (delete, delete) → delete (replace with latest)
	* - (insert, insert) → insert (replace with latest)
	*
	* Note: (delete, update) and (delete, insert) should never occur as the collection
	* layer prevents operations on deleted items within the same transaction.
	*
	* @param existing - The existing mutation in the transaction
	* @param incoming - The new mutation being applied
	* @returns The merged mutation, or null if both should be removed
	*/
	function mergePendingMutations<T extends object>(

I don't know your use case but I can share mine.

With the offline-transactions package, I can persist the transactions and replay them when the network comes back. I then group mutations by globalKey and merge them sequentially using mergePendingMutations through the beforeRetry interface.

[brunobely]

Just ran into this issue and solved it with paced mutations (I used the debounce strategy).

Thanks to @KyleAMathews for pointing it out.