Merging FHIR patients using Firely .NET

Question

I am trying to merge two FHIR patient resources using the C# Firely SDK.

Unfortunately, this always fails with an error

Invalid request. Query parameter sourcePatientId is missing

although it is provided.

Does someone know what I am doing wrong?

Using the same endpoint and parameters in Postman works.

string baseURL = "...";
string targetPatientID = "123-234-5";
string sourcePatientID = "1234-4321-1";

FhirClientsettings settings = new(); // added some headers for auth, etc.
FhirClient client = new(baseURL, settings);

var parameters = new Parameters
{
    { "sourcePatientId", new FhirString(patSource) },
    { "targetPatientId", new FhirString(patTarget) }
};

var uri = new Uri($"{baseUrl}/Patient/$merge", UriKind.Absolute);
Resource mergeResult = await client.OperationAsync(uri, parameters);

Use Fiddler to debug the HTTP request your C# app is sending, compare that to what the Postman console shows. — Ian Kemp - SO dead by AI greed
– Ian Kemp - SO dead by AI greed, Commented Sep 22 at 13:36

Florian · Accepted Answer · 2025-09-23 08:37:44Z

1

The request Patient/$merge needs the parameters added to the URI.

The used method (OperationAsync) turns the parameters into a body and does not add them to the URI. To handle this the following implementation can be used:

var mergeURI = new Uri($"{baseURL}Patient/$merge?sourcePatientId={patSource}&targetPatientId={patTarget}", UriKind.Absolute);
// the empty parameters are needed otherwise it will throw a nullreference exception
Resource mergeResult = await client.OperationAsync(mergeURI, []);

The empty list has to be added to prevent a nullReferenceException

answered Sep 23 at 8:37

Florian

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