CODEWITHSUNDEEP
firebasegoogle-cloud-functions
Grant Singleton
Grant Singleton

Reputation: 1651

Is it always safe to use eventId as the Firestore document id?

This article here recommends using the eventId as the document id to prevent multiple creations of a document due to background process retries. Is it guaranteed that there will never be a collision?

Upvotes: 1

Views: 159

Answers (2)

al-dann
al-dann

Reputation: 2725

From my point of view, an ability to use an event_id as a firestore document id depends on a your context and requirements.

For example - from the "business" point of view - is the message/event really a unique business related thing (thus you really would like to avoid duplication of messages)? Or are there some other business entity which is to be unique, but there can be more than one messages (with different event_id) about that business entity?

On top of that, from the best of my knowledge, it may be a good practice to generate/create the firestore document ids randomly (as a hash, of a guid, etc.). In that case, the search/retrieval from the firestore should work "faster". So, I don't know if the event_id is "random" enough in your context. Maybe it is Ok, may be not...

In my personal experience I try to generate a document id as a hex digest of a hash from a string (may be composed string), which supposed to be unique in the business context. For example, the event/message - is a google.storage.object.finalize event. In that case, I would use some metadata about the underlined object/file. Depends on the business context and requirements, or can be (or not be) a bucket name, object name, size, md5 or crc32c etc. or a combination of those elements... The chosen elements are concatenated into a string, then a hash is calculated, and a hex digest of that hash becomes a document id in the firestore collection.

Upvotes: 1

vitooh
vitooh

Reputation: 4272

Mentioned article is showing how to avoid duplicate item created by retires of unsuccessful function. In shortcut its saying that if you use add method (reference) and function is retried (but failed after Firestore write) you may have a problem with 2 documents identical created in Firestore with different IDs created automatically.

As solution to this author is proposing to create documentID with eventID and write to it using set (refrence).

This approach gives you 100% that retries of the same function invocation will not create duplicate items.

Backing to the question... I think you are afraid that 2 different invocation will want will have the same event_id and the document can be overwritten. This I think is possible, but in my opinion it's not in scope of this article as it's answers different question and creating as simple use case as possible to help understand the approch.

Lets imagine we have to different functions invoked by the same event writing different content to the same collection. The result will be unpredictable, I think. However in such situation you can use the same mechanism, little bit upgraded ex. like this <function_name>_<event_id>. Using the example from the article it will be small change like:

...
return db.collection('contents').doc('<function_name>_'+eventId).set(content).then
...

So in my understanding if you afraid of collision you should add additional elements to created document references, like in the example above.

Upvotes: 1

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