If I'm understanding you correctly, you are providing a list of items with 2 (or more) categories and you want to display them sorted or separated in some way.
The options are multiple requests, one for each selected category. Or a single request allowing the client to specify multiple categories.
If that's in any way close to the correct understanding, this is how I would look at it...
Primarily, right or wrong, seems to be a harsh way to look at it. Advantages and disadvantages might be a less confrontational way to approach it and it might make it easier to come to an agreement.
The advantages of multiple requests:
- API simplicity, Requesting a list of Categories in a single request would add (presumably a small amount) of complexity to the API which may be unnecessary if you don't expect complex requests
- Interface simplicity, No filtering code in the interface.
- Fairly large records (lots of data, compared to the overhead of the connection) in a situation where multi category requests are the exception would be one situation where this would work.
Advantages of a single request:
- There is a non-trivial amount of overhead to the additional connections. This is compounded by things like cookies which on some sites can add up to a significant percentage of the request/response bandwidth for small images and ajax requests.
- An environment where multiple category requests are the norm especially if the records (and number of results) are small would favor this approach.
In general, I would say less requests is absolutely what you would want to aim for. But you really need to evaluate your individual situation and take into account a wider picture of the system and how it is likely to be used. And this may change over time. A system designed with a total of 3 categories, that grows over time to hundreds of categories would probably need to be reevaluated.