Add monger.collection/system-collection?, a convenience function

We don't add it to the change log because the majority of apps won't use it and
it is not an important change between RC1 and RC2 (or what may even be 1.0).

src/monger/collection.clj

@@ -612,3 +612,17 @@
     ;; this is what DBCollection#distinct does. Turning a blind eye!
     (.throwOnError res)
     (map #(from-db-object % true) (.get res "result"))))
+
+
+;;
+;; Misc
+;;
+
+(def ^{:const true}
+  system-collection-pattern #"^(system|fs)")
+
+(defn- system-collection?
+  "Evaluates to true if the given collection name refers to a system collection. System collections
+   are prefixed with system. or fs. (default GridFS collection prefix)"
+  [^String coll-name]
+  (re-find system-collection-pattern coll-name))

test/monger/test/collection_test.clj

@@ -132,3 +132,22 @@
     (mc/insert-batch collection batch)
     (is (= ["CA" "IL" "NY"] (sort (mc/distinct mg/*mongodb-database* collection :state {}))))
     (is (= ["CA" "NY"] (sort (mc/distinct collection :state {:price {$gt 100.00}}))))))
+
+
+;;
+;; miscellenous
+;;
+
+(deftest test-system-collection-predicate
+  (are [name] (is (mc/system-collection? name))
+    "system.indexes"
+    "system"
+    ;; we treat default GridFS collections as system ones,
+    ;; possibly this is a bad idea, time will tell. MK.
+    "fs.chunks"
+    "fs.files")
+  (are [name] (is (not (mc/system-collection? name)))
+    "events"
+    "accounts"
+    "megacorp_account"
+    "myapp_development"))