Add FhirEngine interface method 'withTransaction'

engine/src/main/java/com/google/android/fhir/FhirEngine.kt

@@ -202,6 +202,12 @@ interface FhirEngine {
    *   back and no record is purged.
    */
   suspend fun purge(type: ResourceType, ids: Set<String>, forcePurge: Boolean = false)
+
+  /**
+   * Adds support for performing actions on `FhirEngine` as a single atomic transaction where the
+   * entire set of changes succeed or fail as a single entity
+   */
+  suspend fun withTransaction(block: suspend FhirEngine.() -> Unit)
 }
 
 /**

engine/src/main/java/com/google/android/fhir/impl/FhirEngineImpl.kt

@@ -97,6 +97,10 @@ internal class FhirEngineImpl(private val database: Database, private val contex
     }
   }
 
+  override suspend fun withTransaction(block: suspend FhirEngine.() -> Unit) {
+    database.withTransaction { this.block() }
+  }
+
   private suspend fun saveResolvedResourcesToDatabase(resolved: List<Resource>?) {
     resolved?.let {
       database.deleteUpdates(it)

engine/src/main/java/com/google/android/fhir/testing/Utilities.kt

@@ -176,6 +176,8 @@ internal object TestFhirEngineImpl : FhirEngine {
     download().collect()
   }
 
+  override suspend fun withTransaction(block: suspend FhirEngine.() -> Unit) {}
+
   override suspend fun count(search: Search): Long {
     return 0
   }

engine/src/test/java/com/google/android/fhir/impl/FhirEngineImplTest.kt

@@ -48,12 +48,16 @@ import kotlinx.coroutines.test.runTest
 import org.hl7.fhir.exceptions.FHIRException
 import org.hl7.fhir.r4.model.Address
 import org.hl7.fhir.r4.model.CanonicalType
+import org.hl7.fhir.r4.model.CodeableConcept
 import org.hl7.fhir.r4.model.Coding
 import org.hl7.fhir.r4.model.DateTimeType
+import org.hl7.fhir.r4.model.Encounter
 import org.hl7.fhir.r4.model.Enumerations
 import org.hl7.fhir.r4.model.HumanName
 import org.hl7.fhir.r4.model.Meta
+import org.hl7.fhir.r4.model.Observation
 import org.hl7.fhir.r4.model.Patient
+import org.hl7.fhir.r4.model.Reference
 import org.hl7.fhir.r4.model.ResourceType
 import org.junit.Assert.assertThrows
 import org.junit.Before
@@ -783,6 +787,71 @@ class FhirEngineImplTest {
     assertThat(services.database.getLocalChangesCount()).isEqualTo(0)
   }
 
+  @Test
+  fun `withTransaction saves changes successfully`() = runTest {
+    fhirEngine.withTransaction {
+      val patient01 =
+        Patient().apply {
+          id = "patient-01"
+          gender = Enumerations.AdministrativeGender.FEMALE
+        }
+      this.create(patient01)
+
+      val patient01Observation =
+        Observation().apply {
+          id = "patient-01-observation"
+          status = Observation.ObservationStatus.FINAL
+          code = CodeableConcept()
+          subject = Reference(patient01)
+        }
+      this.create(patient01Observation)
+    }
+
+    assertThat(
+        fhirEngine.get<Patient>("patient-01"),
+      )
+      .isNotNull()
+    assertThat(fhirEngine.get<Observation>("patient-01-observation")).isNotNull()
+    assertThat(
+        fhirEngine.get<Observation>("patient-01-observation").subject.reference,
+      )
+      .isEqualTo("Patient/patient-01")
+  }
+
+  @Test
+  fun `withTransaction rolls back changes when an error occurs`() = runTest {
+    val patient01 =
+      Patient().apply {
+        id = "patient-01"
+        gender = Enumerations.AdministrativeGender.FEMALE
+      }
+
+    fhirEngine.create(patient01)
+
+    try {
+      fhirEngine.withTransaction {
+        val patientEncounter =
+          Encounter().apply {
+            id = "enc-01"
+            status = Encounter.EncounterStatus.FINISHED
+            class_ = Coding()
+            subject = Reference(patient01)
+          }
+
+        this.create(patientEncounter)
+
+        // Update encounter to reference non-existent subject to force ResourceNotFoundException
+        val nonExistentSubject = this.get(ResourceType.Patient, "non_existent_id") as Patient
+        patientEncounter.subject = Reference(nonExistentSubject)
+        this.update(patientEncounter)
+      }
+    } catch (_: ResourceNotFoundException) {}
+
+    assertThrows(ResourceNotFoundException::class.java) {
+      runBlocking { fhirEngine.get<Encounter>("enc-01") }
+    }
+  }
+
   companion object {
     private const val TEST_PATIENT_1_ID = "test_patient_1"
     private var TEST_PATIENT_1 =