add helper function for checking if a resource has been deleted or not

README.md

@@ -426,6 +426,11 @@ resource to be deleted. The return value will typically be `nil` on success, tho
 some servers may return an OperationOutcome resource that includes more details about
 the successful deletion.
 
+You can use the helper function `deleted?` to determine if a resource has been deleted
+or not, since `get-resource` returns nil for both deleted resources and resources
+which do not exist at all (an important distinction, as in FHIR a deleted resource
+technically still exists under previous version numbers).
+
 ##### Examples
 
 ```clojure
@@ -440,6 +445,14 @@ the successful deletion.
 ; try to delete a non-existant patient
 (delete server-url :patient 9001)
 => ExceptionInfo FHIR request failed: HTTP 404
+
+; testing if a resource has been deleted or not
+(deleted? server-url :patient 1654)
+=> true
+
+; testing if a non-existant resource has been deleted
+(deleted? server-url :patient 9001)
+=> false
 ```
 
 ### Error Handling

src/clj_hl7_fhir/core.clj

@@ -365,6 +365,24 @@
       base-url
       (apply join-paths uri-components))))
 
+(defn deleted?
+  [base-url type id]
+  (let [resource-name  (->fhir-resource-name type)
+        url-components ["/" resource-name id]
+        relative-url   (apply join-paths url-components)]
+    (try
+      (fhir-request :get
+                    base-url
+                    relative-url)
+      ; not deleted
+      false
+      (catch ExceptionInfo ex
+        (let [http-status (:status (ex-data ex))]
+          (cond
+            (= http-status 410) true
+            (= http-status 404) false
+            :else               (throw ex)))))))
+
 ;(def server-url "http://fhir.healthintersections.com.au/open")
 ;(def server-url "http://spark.furore.com/fhir")
 ;(def server-url "http://fhirtest.uhn.ca/base")