Make $merge Feature Optional in JPA Server (Avoid Mandatory Patient DAO Requirement) #7380
Description
Summary
The $merge feature in the HAPI FHIR JPA Server is currently initialized unconditionally. As a result, several merge-related services (MergeValidationService, ResourceMergeService, MergeProvenanceSvc, and merge providers) require the existence of certain DAOs — most notably the Patient DAO.
When a deployment intentionally limits supported_resource_types (e.g., to only Organization or HealthcareService), these DAOs do not exist in the DaoRegistry. This causes the server to fail during startup with errors such as:
`No DAO exists for resource type class org.hl7.fhir.r4.model.Patient``
This makes it impossible to run a minimal or restricted JPA Server instance without implicitly supporting Patient, even when $merge is not needed.
Expected Behavior
- $merge should be fully optional at the JPA-layer.
- If a server disables resource merge:
- No merge-related beans should be constructed.
- No DAOs for specific resource types (such as Patient) should be required.
- No $merge operations should be exposed via REST.
- The default behavior must remain fully backward-compatible.
Environment
• HAPI FHIR version: 8.4
• Module: JPA Server (core), R4/R5 configs
• Relevant area: Merge Services and $merge provider registration