Why is the return type from upsert Partial?

[eXamadeus]

First, I love this library! It's amazing. I tried others, and there is no comparison.

So, to my question... I've been trying to use the upsert mechanism for a few things, and I'm confused about the upsert return type. Whenever I make the upsert call, the data type is Partial, which confuses me. Shouldn't this ALWAYS return a result like create?

Here is a playground link to show what I'm talking about.

This may be the expected behavior since I'm new to DynamoDB and expect it to work like the create method. Is it partial because it doesn't perform a query (just the update), and thus, it can't know what the entire object looks like? If so, that makes sense. It might help to outline that in the documentation.

[tywalch]

Let me look into this, I agree at first glance 👍

[tywalch]

@eXamadeus 👋

I looked into this and found why the return typing is not the same as create or put. The create and put have the response type they do because the values you pass will be the values you write; both methods use DynamoDB put under the hood so they will both overwrite any existing value. The upsert method, while having a similar interface to create and put, does not necessarily write the same values that it receives. Two notable examples:

1. The upsert operation can also perform an update which means even if the method returned the values provided, it would not be reflective of the item in the database.
2. The values passed to the add, subtract, append and ifNotExists methods on upsert can result in a different value in the database than what was provided. Readonly values get automatically added as ifNotExists, so these values could also be different.

This is why upsert does not have the same response by default as create and put. That said, you can easily get the same response by using the execution option .go({ response: 'all_new' }) to return the stored item as it exists after write 👍