public virtual async Task <string> SaveObservationAsync(ILookupTemplate <IFhirTemplate> config, IObservationGroup observationGroup, IDictionary <ResourceType, string> ids)
{
var identifier = GenerateObservationIdentifier(observationGroup, ids);
var cacheKey = $"{identifier.System}|{identifier.Value}";
if (!_observationCache.TryGetValue(cacheKey, out Model.Observation existingObservation))
{
existingObservation = await GetObservationFromServerAsync(identifier).ConfigureAwait(false);
// Discovered an issue where FHIR Service is only matching on first 128 characters of the identifier. This is a temporary measure to prevent merging of different observations until a fix is available.
if (existingObservation != null && !existingObservation.Identifier.Exists(i => i.IsExactly(identifier)))
{
throw new NotSupportedException("FHIR Service returned matching observation but expected identifier was not present.");
}
}
var policyResult = await Policy <(Model.Observation observation, ResourceOperation operationType)>
.Handle <FhirException>(ex => ex.StatusCode == System.Net.HttpStatusCode.Conflict || ex.StatusCode == System.Net.HttpStatusCode.PreconditionFailed)
.RetryAsync(2, async(polyRes, attempt) =>
{
// 409 Conflict or 412 Precondition Failed can occur if the Observation.meta.versionId does not match the update request.
// This can happen if 2 independent processes are updating the same Observation simultaneously.
// or
// The update operation failed because the Observation no longer exists.
// This can happen if a cached Observation was deleted from the FHIR Server.
_logger.LogTrace("A conflict or precondition caused an Observation update to fail. Getting the most recent Observation.");
// Attempt to get the most recent version of the Observation.
existingObservation = await GetObservationFromServerAsync(identifier).ConfigureAwait(false);
// If the Observation no longer exists on the FHIR Server, it was most likely deleted.
if (existingObservation == null)
{
_logger.LogTrace("A cached version of an Observation was deleted. Creating a new Observation.");
// Remove the Observation from the cache (this version no longer exists on the FHIR Server.
_observationCache.Remove(cacheKey);
}
})
.ExecuteAndCaptureAsync(async() =>
{
if (existingObservation == null)
{
var newObservation = GenerateObservation(config, observationGroup, identifier, ids);
return(await _fhirService.CreateResourceAsync(newObservation).ConfigureAwait(false), ResourceOperation.Created);
}
// Merge the new data with the existing Observation.
var mergedObservation = MergeObservation(config, existingObservation, observationGroup);
// Check to see if there are any changes after merging and update the Status to amended if changed.
if (!existingObservation.AmendIfChanged(mergedObservation))
{
// There are no changes to the Observation - Do not update.
return(existingObservation, ResourceOperation.NoOperation);
}
// Update the Observation. Some failures will be handled in the RetryAsync block above.
return(await _fhirService.UpdateResourceAsync(mergedObservation).ConfigureAwait(false), ResourceOperation.Updated);
}).ConfigureAwait(false);
var exception = policyResult.FinalException;
if (exception != null)
{
throw exception;
}
var observation = policyResult.Result.observation;
_logger.LogMetric(IomtMetrics.FhirResourceSaved(ResourceType.Observation, policyResult.Result.operationType), 1);
_observationCache.CreateEntry(cacheKey)
.SetAbsoluteExpiration(DateTimeOffset.UtcNow.AddHours(1))
.SetSize(1)
.SetValue(observation)
.Dispose();
return(observation.Id);
}