ServiceRequest search by resolve()

[whyfate]

Describe the bug

var sr = new ServiceRequest
{
    Subject = new ResourceReference
    {
        Reference="Patient/1",
    }
};
// values Count is 0
var values = sr.ToTypedElement().Select("ServiceRequest.subject.where(resolve() is Patient)");

But the similar cases

Patient patient = new()
{
    Id = "1",
    Active = true,
    BirthDate = "2001-03-01"
};

Encounter encounter = new()
{
    Contained = new List<Resource>() { patient },
    Subject = new ResourceReference("#1")
};
// values Count is 1
var values = encounter.Select("Encounter.subject.where(resolve() is Patient)");

I use 3.3.0 version of firely-net-sdk.

[marcovisserFurore]

Hi @whyfate ,

In your second example FhirPath can resolve the Patient, because this resource is contained in the Encounter resource. So FhirPath is able to find this resource. In your first example the ServiceRequest is reference to a non-contained resource. That means that the resource can be on the same server, but even on a complete other server. FhirPath cannot determine that.

To overcome that, you can tell FhirPath how to resolve resource, like this:

            var context = FhirEvaluationContext.CreateDefault();

            var client = new FhirClient("https//fhir.server.example");
            var resolver = new WebResolver((uri) => client);

            context.ElementResolver = (s) => resolver.ResolveByCanonicalUri(s).ToTypedElement();
            var values = sr.Select("ServiceRequest.subject.where(resolve() is Patient)", context);

In this case we tell FhirPath to request the server "https//fhir.server.example" to retrieve the resource. Assuming the resource (ServiceRequest) is on that server.

[whyfate]

It's so complicated.

[marcovisserFurore]

It is. But maybe you can explain your use case, and then there might be a better solution. For example, is your use case to retrieve ServiceRequest resources from a Fhir server with subject is Patient? Then you can write a search request to the server a let the server do the filtering.

[whyfate]

I use spark as fhir server.
I read the docs(http://build.fhir.org/servicerequest.html#search), I want to search the ServiceRequest by patient.

spark is not implemented.
I tried to modify the code, so complicated.

[kennethmyhra]

I have never worked with resolvers in the firely-net-sdk library. For Spark would probably need to implement a custom resource resolver (IAsyncResourcesResolver/IResourceResolver) that can resolve resources from the database.

[whyfate]

@kennethmyhra It's will be slowly.Maybe I don't want to verify whether it really exists.

[kennethmyhra]

There exists no such resolver server-side in Spark today.

But I think Marco's example using the WebResolver client-side should be quite easy to implement without having to modify Spark's source code. Speed will of course depend on how many such resolve call you need to issue.

[whyfate]

Emmm...but isn't that what the server should provide?

[kennethmyhra]

I have not worked much with FHIRPath and resolve, but I don't think there is a good way in the specification to issue such a FHIRPath to the server from a client?

[whyfate]

@kennethmyhra @marcovisserFurore Thank you very much for your answers.
I'll use subject to instead of patient to search ServiceRequest.
This is best way for me right now.

[marcovisserFurore]

I moved this issue to the discussion section, because it is not related to a bug in the SDK, but can be used for future references.