add support for :_include modifier

[simonvadee]

Description

The search is not yet able to handle the _include modifier which allows to "join" resources between them.
For instance, the query string /Observation?category=laboratory&_include=Observation:encounter which is equivalent to

search_context = SearchContext(engine, "Observation")
params = (("category", "laboratory"), ("_include", "Observation:encounter"))
fhir_search = Search(search_context,  params=params)

should output a Bundle like:

{
    "id": "1",
    "meta": {},
    "entry": [
        {
            "fullUrl": "Observation/123",
            "resource": {
                "...": "...",
                "resourceType": "Observation"
            },
            "search": {
                "mode": "match"
            }
        },
        {
            "fullUrl": "Encounter/456",
            "resource": {
                "...": "...",
                "resourceType": "Encounter"
            },
            "search": {
                "mode": "include"
            }
        }
    ],
    "link": [
        {
            "relation": "self",
            "url": "https://some.url"
        }
    ],
    "total": 1,
    "type": "searchset",
    "resourceType": "Bundle"
}

I'm not sure how we should implement "relations" between documents but the parent-child relationship using the join datatype seems to be a good fit.
A first implementation could also consist in running multiple ES queries and construct a bundle from multiple results.

[nazrulworld]

Thank you much for this issue :). Yes fully agree about the complexity in implementation, we will need collaborative efforts.
I think we will wait a little bit for this feature until next release done, right now I am waiting for https://pypi.org/project/fhir.resources/ new release (it will bring massive changes and improvements) so next release of fhirpath will be compatible with fhir.resources 6.x.x.

[simonvadee]

That's great news, the new version of fhir.resources looks great! Do you have an idea of when the new compatible version of fhirpath will be ready ? Is there anything I can do to help ?

[nazrulworld]

Making compatible is in progress, hope will be completed soon. I will invite you soon for this include feature 😃.
Thanks a lot for your support.

[nazrulworld]

@simonvadee I think current implementations are already compatible with the latest fhir.resources. You are welcome 🙏 to start working on supporting the _include modifier.