It's something we debated in our team: if there's an API that returns data based on filters, what's the better behavior if no filters are provided - return everything or return nothing?

The consensus was that returning everything is rarely what's desired, for two reasons: first, if the system grows, allowing API users to return everything at once can be a problem both for our server (lots of data in RAM when fetching from the DB => OOM, and additional stress on the DB) and for the user (the same problem on their side). Second, it's easy to forget to specify filters, especially in cases like "let's delete something based on some filters."

So the standard practice now is to return nothing if no filters are provided, and we pay attention to it during code reviews. If the user does really want all the data, you can add pagination to your API. With pagination, it's very unlikely for the user to accidentally fetch everything because they must explicitly work with pagination tokens, etc.

Another option, if you don't want pagination, is to have a separate method named accordingly, like ListAllObjects, without any filters.

Returning an empty result in that case may cause a more subtle failure. I would think returning an error would be a bit better as it would clearly communicate that the caller called the API endpoint incorrectly. If it’s HTTP a 400 Bad Request status code would seem appropriate.

>allowing API users to return everything at once can be a problem both for our server (lots of data in RAM when fetching from the DB => OOM, and additional stress on the DB)

You can limit stress on RAM by streaming the data. You should ideally stream rows for any large dataset. Otherwise, like you say you are loading the entire thing into RAM.

I like your thought process around the ‘empty’ case. While the opposite of a filter is no filter, to your point, that is probably not really the desire when it comes to data retrieval. We might have to revisit that ourselves.