with-db macro to provide local binding of current db, with test

src/somnium/congomongo.clj

@@ -130,6 +130,15 @@ object may be passed as the last argument."
        (binding [*mongo-config* c#]
          ~@body))))
 
+(defmacro with-db
+  "Make title the active database in the enclosing scope.
+
+  When with-db and set-database! interact, last one wins."
+  [title & body]
+  `(let [db# (.getDB (:mongo *mongo-config*) (name ~title))]
+     (binding [*mongo-config* (assoc *mongo-config* :db db#)]
+       ~@body)))
+
 (defn set-connection!
   "Makes the connection active. Takes a connection created by make-connection.
 

test/somnium/test/congomongo.clj

@@ -79,6 +79,16 @@
       ;; check a default option as well
       (is (not (.slaveOk opts))))))
 
+(deftest with-mongo-database
+  (with-test-mongo
+    (let [a (make-connection "congomongotest-db-a" :host test-db-host :port test-db-port)]
+      (with-mongo a
+        (with-db "congomongotest-db-b"
+          (testing "with-mongo uses new database"
+                   (is (= "congomongotest-db-b" (.getName (*mongo-config* :db))))))
+        (testing "with-mongo uses connection db "
+                 (is (= "congomongotest-db-a" (.getName (*mongo-config* :db)))))))))
+
 (deftest with-mongo-interactions
   (with-test-mongo
     (let [a (make-connection "congomongotest-db-a" :host test-db-host :port test-db-port)