Consuming FHIR Client API with SQL-like ideas - hl7-fhir

Question

I'm new to the FHIR World, I have a FHIR client, HAPI FHIR that I can use to fetch data through a restful API. I apology if I missunderstand something during my FHIR documentation journey.
I've look around the documentation and tried some requests to fetch basic data, like a list of Patient, an Observation by id etc..
In my case, I need to get a list of Patient that have the same name as its resource generalPractioner (it's unlikely to happen, it's just an example).
In regular SQL it would look like something like this :
SELECT * FROM Patient
INNER JOIN Practitioner ON Practitioner.id = Patient.practitioner_id
WHERE Patient.name = Practitioner.name
Since FHIR doesn't work that way and isn't relational database, I need to come up with a way to do the equivalent of SQL's WHERE and SQL's JOIN but through the restful API of the client.
My questions are : Is it possible to do these kind of thing directly on a FHIR Client through the API ? If yes, do I need to make new modules inside HAPI FHIR (JPA or plain server ?) (using Java) so it can understand what I really want ?(a new parser with a new route on each resource for example).
Note that the example with the SQL query is pretty simple, my project is to be able to do really nested joins and wheres, as well as the SQL's AND and OR. It doesn't have to use graphQL, this is just what matches the most with my idea while I was reading the documentation.
I'm afraid that regular _include, _filter and _search parameters aren't enough for what I need.
I found that the fhirpath thing could be use but I didn't find how to use it through the API (except with the $graphql operation).
Seems like ChatGPT want me to use the operation $fhirql which is no longer supported in the recent versions of HAPI FHIR, this seemed to be wnat I want.
Thanks !

Answer 1

I do not know what $fhirql is - and I think I know everything there is to know about FHIR. And Google comes up blank, so that might be ChatGPT just fantasising again. Maybe it invented that based on https://github.com/FirelyTeam/FhirQuery, which is clearly the kind of thing you're thinking about.
Or maybe Pathling is closer to what you want: https://pathling.csiro.au.
$graphql only lets you filter your data, it doesn't allow de novo new joins. _filter is the nearest to what you want, for the few servers that support it, but even then, no joins the way you want.
So it looks like you'll have to fetch the data from your API by a client, and then do something locally, which is how those tools work. Unless the server does something specific for you