REST: Get multiple resources - what is correct REST approach

I know this question has been answered several times, but I am still not sure that providing GET with long list of non-structured query parameters or POST to get data is right approach.

I have provided the endpoint:

GET /businessrelationships/{brGlobalKey}

Which returns one resource/object. I would like to provide GET endpoint (as this is safe method) to get predefined list of objects. I was thinking to firstly use POST to create new resource, Lists:

POST /businessrelationships/{brGlobalKey}/lists

with Body : {
  "brGlobalKeys": [
    1234,
    212354,
    3748
  ]
}

The POST will be idempotent and will return listID, for example 123xyz. I would then provide GET to retrieve list with multiple objects:

GET /businessrelationships/{brGlobalKey}/lists/123xyz

Please let me know is this correct method? I know that using 2 instead of 1 call will affect performances, but it is up to the consumer to decide if they want to GET single resource several times or to use list.

Thanks

Solution

I would not recommend to create a separate resource called list. And I think even if you wanted to have a separate resource, it does not make sense as a sub resource of businessRelationship.

If the list of the brGlobalIKeys filter is not too extensive (your example suggests that common API use cases need a handful of keys) I would recommend to use a query string parameter for that taking a comma-separated list of keys and return a filtered array of business relationships. This removes complexity from your service (you don't need to manage the lists of keys) and the client is quite flexible without making additional calls to preconfigure/change the list resource.

Example: https://base.com/businessRelationships?filteredKeys=123,234,345