Conditional References in HAPI FHIR

HL7 FHIR Release 3 (STU) introduced the concept of Conditional References in transaction bundles:

When constructing the bundle, the client may not know the logical id of a resource, but it may know identifying information - e.g. an identifier. This situation arises commonly when building transactions from v2 messages. The client could resolve that identifier to a logical id using a search, but that would mean that the resolution to a logical id does not occur within the same transaction as the commit (as well as significantly complicating the client). Because of this, in a transaction (and only in a transaction), references to resources may be replaced by a search URI that describes how to find the correct reference:

<Bundle xmlns="http://hl7.org/fhir">
    <id value="20160113160203" />
    <type value="transaction" />
    <entry>
        <fullUrl value="urn:uuid:c72aa430-2ddc-456e-7a09-dea8264671d8" />
        <resource>
            <Observation>
                <subject>
                    <reference value="Patient?identifier=12345" />
                </subject>
                <!-- rest of resource omitted -->
            </Observation>
        </resource>
        <request>
            <method value="POST" />
        </request>
    </entry>
</Bundle>

The search URI is relative to the server's [base] path, and always starts with a resource type: [type]:?parameters.... Only filtering parameters are allowed; none of the parameters that control the return of resources are relevant.

When processing transactions, servers SHALL:

check all references for search URIs
For search URIs, use the search to locate matching resources
if there are no matches, or multiple matches, the transaction fails, and an error is returned to the user
if there is a single match, the server replaces the search URI with a reference to the matching resource

... quoted from 2.21.0.17.2 Transaction Processing Rules

I found this concept of conditional references very useful and I would like to use it in my HAPI FHIR client/server app. It seems that it is not supported. Such transaction bundle is refused by server with following error messages:

Client:

HTTP 400 Bad Request: Invalid resource reference found at path[Observation.subject] - Does not contain resource type - Patient?identifier=12345

Exception in thread "main" ca.uhn.fhir.rest.server.exceptions.InvalidRequestException: HTTP 400 Bad Request: Invalid resource reference found at path[Observation.subject] - Does not contain resource type - Patient?identifier=12345
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at ca.uhn.fhir.rest.server.exceptions.BaseServerResponseException.newInstance(BaseServerResponseException.java:307)
    at ca.uhn.fhir.rest.client.BaseClient.invokeClient(BaseClient.java:290)
    at ca.uhn.fhir.rest.client.GenericClient$BaseClientExecutable.invoke(GenericClient.java:637)
    at ca.uhn.fhir.rest.client.GenericClient$TransactionExecutable.execute(GenericClient.java:2209)

Server log:

WARN c.u.f.r.s.i.ExceptionHandlingInterceptor [ExceptionHandlingInterceptor.java:135] Failure during REST processing: ca.uhn.fhir.rest.server.exceptions.InvalidRequestException: Invalid resource reference found at path[Observation.subject] - Does not contain resource type - Patient?identifier=12345

So my question is:

Is it possible to use conditional references with HAPI FHIR JPA server?

Or if it is not possible, is there work around? Can I use same conditional operation which would resolve the reference or fail if the reference target doesn't exist?

Solution

Finally I discovered that it is possible even with HAPI FHIR vesion 2.2 simply by adding following option to the server DaoConfig:

ca.uhn.fhir.jpa.dao.DaoConfig.setAllowInlineMatchUrlReferences(true)

Should references containing match URLs be resolved and replaced in create and update operations. For example, if this property is set to true and a resource is created containing a reference to Patient?identifier=12345, this is reference match URL will be resolved and replaced according to the usual match URL rules.

Default is false for now, as this is an experimental feature.

See the source code here: github.com/jamesagnew/hapi-fhir