Search the local store

Goal and scope​

Everything the engine stores is indexed for search. When a resource is written, its search-parameter FHIRPath expressions are evaluated and the values land in typed index tables. This page covers querying that index with the DSL in dev.ohs.fhir.engine.search.

The search DSL​

search<R> takes a block configuring the query. An empty block matches every resource of the type.

import dev.ohs.fhir.engine.search.Order
import dev.ohs.fhir.engine.search.StringClientParam
import dev.ohs.fhir.engine.search.search
import dev.ohs.fhir.model.r4.Patient

val results = fhirEngine.search<Patient> {
  filter(StringClientParam("name"), { value = "Jo" })
  sort(StringClientParam("name"), Order.ASCENDING)
}

val patients = results.map { it.resource }

Each hit is a SearchResult carrying the matched resource, plus any included resources when the query asks for them.

Typed parameters per FHIR search type​

The DSL mirrors FHIR's search parameter types with one filter class each.

The parameter name is the FHIR search parameter's name ("name", "birthdate", "identifier", and so on). Comparable types take a prefix alongside the value, mirroring FHIR's search prefixes.

import dev.ohs.fhir.engine.search.NumberClientParam
import dev.ohs.fhir.model.r4.SearchParameter.SearchComparator

filter(
  NumberClientParam("probability"),
  {
    prefix = SearchComparator.Gt
    value = threshold
  },
)

Beyond flat filters, the DSL supports nested searches on referenced resources, forward includes and reverse includes to fetch related resources in one query, and count<R> { ... } when you need the number of matches without materializing them.

String queries​

search(xFhirQuery: String) accepts an x-fhir-query string ("Patient?name=Jo") for queries that arrive as data. Its translator supports plain parameter matching and sorting only. There are no modifiers, prefixes, chained parameters, global common parameters, or embedded FHIRPath. When you control the query at compile time, prefer the typed DSL.

What is queryable​

• Indexing happens at write time, driven by the standard R4 search-parameter definitions. Parameters whose FHIRPath expressions the FHIRPath engine cannot evaluate, such as resolve()-based ones, are skipped, so those parameters return no results rather than failing.
• Custom search parameters can be supplied at initialization through customSearchParameters in FhirEngineConfiguration. They add to the spec-defined parameters and must not redefine existing ones.

Checkpoint​

Searching StringClientParam("name") for a prefix of a stored patient's name returns that patient. A resource that a filter unexpectedly misses usually means the relevant search parameter is not indexed. Check the parameter's FHIRPath expression against the supported surface.

Next step​

Synchronize with a server. The change log you have been silently writing becomes an upload.