Challenges with _count and total in HAPI

[keithboone]

Keith Boone: I'm working on pagination in my server (not using PaginationProvider), returning a Bundle. It appears that HAPI is rewriting the bundle I return and changing the value of Total to -1 (one of my test cases is for _count=-1, which seems to be related). I suspect I need to return an IBundleProvider or something, but thought I would mention the weird behavior.

Keith Boone: Issue appears to be in BaseMethodBinding.toResourceList() method.

Keith Boone: Tracked it back to BaseResourceReturningMethodBinding. doInvokeServer(IRestfulServer<?> theServer, RequestDetails theRequest) where: Integer count = RestfulServerUtils.extractCountParameter(theRequest); ... And then: bundleFactory.addRootPropertiesToBundle(null, theRequest.getFhirServerBase(), linkSelf, null, null, count, getResponseBundleType(), lastUpdated);

BUT: count is clearly not theTotalResults, and in fact, there's really no way to know what that value SHOULD be based on the response unless Bundle.total is populated.

I'll log a bug for this, and see what I can do to work around it.

To Reproduce Steps to reproduce the behavior: Create a ResourceProvider that returns a Bundle that does not populate total, and supports _count, and pass in a _count value to the query.

The _count value is used for the Bundle.total (even though that's not right).

Expected behavior Total should be not be altered from what was returned.

Environment (please complete the following information):

• HAPI FHIR Version: 4.0.1
• OS: N/A (but I'm testing on Windows 10 and deploying to Linux Docker containers)

Additional context See https://chat.fhir.org/#narrow/stream/179167-hapi/topic/Challenges.20with.20_count.20and.20total.20in.20HAPI

Total should not be overwritten, even when not present. The HAPI Server has NO clue what the right value should be, and cannot know.

[keithboone]

Workaround follows:

1. Add RequestDetails theDetails to your query method if not already present.

2. Add this before you return the bundle. It removes _count from theDetails so it won't be changed if there is no total, or sets it to the actual total.

   // This is a hack to work around https://github.com/jamesagnew/hapi-fhir/issues/1585
   // We remove the _count parameter from theDetails so that total is not modified.
   Map<String, String[]> params = new HashMap<String, String[]>(theDetails.getParameters());
   Integer total = bundle.hasTotal() ? null : bundle.getTotal();
   if (params.remove(Constants.PARAM_COUNT) != null || total != null) {
       if (total != null) {
           params.put(Constants.PARAM_COUNT, new String[] { total.toString() });
       }
       // Remove _count parameter from the current request details
       theDetails.setParameters(params);
   }
   
   return bundle;

[RickHawesUSDS]

Thanks for this issue report. I ran into the same bug where the HAPI server code was adding a total (an incorrect one at that) when my Bundle didn't have one before. This report helped me work-around the issue.