small tweak to driver initialization code.

src/metabase/core.clj

@@ -15,6 +15,7 @@
             [medley.core :as m]
             (metabase [config :as config]
                       [db :as db]
+                      [driver :as driver]
                       [events :as events]
                       [middleware :as mb-middleware]
                       [routes :as routes]
@@ -122,6 +123,9 @@
   (.addShutdownHook (Runtime/getRuntime) (Thread. ^Runnable destroy))
   (reset! metabase-initialization-progress 0.3)
 
+  ;; Load up all of our Database drivers, which are used for app db work
+  (driver/find-and-load-drivers!)
+
   ;; startup database.  validates connection & runs any necessary migrations
   (db/setup-db :auto-migrate (config/config-bool :mb-db-automigrate))
   (reset! metabase-initialization-progress 0.5)

src/metabase/driver.clj

@@ -231,23 +231,30 @@
   (swap! registered-drivers assoc engine driver-instance)
   (log/debug (format "Registered driver %s." engine)))
 
-(def ^:private load-driver-namespaces!
-  "Search the classpath for metabase driver namespaces and `require` them, so they are \"registered\" and can be used :heart_eyes_cat:"
-  (delay (doseq [namespce (filter (fn [ns-symb]
-                                    (re-matches #"^metabase\.driver\.[a-z0-9_]+$" (name ns-symb)))
-                                  (ns-find/find-namespaces (classpath/classpath)))]
-           (require namespce))))
-
 (defn available-drivers
   "Info about available drivers."
   []
-  @load-driver-namespaces!
   (m/map-vals (fn [driver]
                 {:details-fields (details-fields driver)
                  :driver-name    (name driver)
                  :features       (features driver)})
               @registered-drivers))
 
+(defn find-and-load-drivers!
+  "Search Classpath for namespaces that start with `metabase.driver.`, then `require` them and look for the `driver-init`
+   function which provides a uniform way for Driver initialization to be done."
+  []
+  ;; TODO: at some point if we want to allow true 3rd party drivers we should provide a way for this loading to
+  ;;       include drivers defined in other namespace patterns, probabaly via some kind of config which is passed to us
+  (doseq [namespce (filter (fn [ns-symb]
+                             (re-matches #"^metabase\.driver\.[a-z0-9_]+$" (name ns-symb)))
+                           (ns-find/find-namespaces (classpath/classpath)))]
+    (log/info "\tloading driver namespace: " namespce)
+    (require namespce)
+    ;; look for `driver-init` function in the namespace and call it if it exists
+    (when-let [init-fn (ns-resolve namespce 'driver-init)]
+      (init-fn))))
+
 (defn is-engine?
   "Is ENGINE a valid driver name?"
   [engine]

src/metabase/driver/h2.clj

@@ -217,4 +217,6 @@
           :string-length-fn          (constantly :LENGTH)
           :unix-timestamp->timestamp unix-timestamp->timestamp}))
 
-(driver/register-driver! :h2 (H2Driver.))
+(defn driver-init
+  []
+  (driver/register-driver! :h2 (H2Driver.)))

src/metabase/driver/mongo.clj

@@ -161,4 +161,6 @@
           :sync-in-context                   sync-in-context
           :table-pks                         (constantly #{"_id"})}))
 
-(driver/register-driver! :mongo (MongoDriver.))
+(defn driver-init
+  []
+  (driver/register-driver! :mongo (MongoDriver.)))

src/metabase/driver/mysql.clj

@@ -175,4 +175,6 @@
           :set-timezone-sql          (constantly "SET @@session.time_zone = ?;")
           :unix-timestamp->timestamp unix-timestamp->timestamp}))
 
-(driver/register-driver! :mysql (MySQLDriver.))
+(defn driver-init
+  []
+  (driver/register-driver! :mysql (MySQLDriver.)))

src/metabase/driver/postgres.clj

@@ -201,4 +201,6 @@
           :string-length-fn          (constantly :CHAR_LENGTH)
           :unix-timestamp->timestamp unix-timestamp->timestamp}))
 
-(driver/register-driver! :postgres (PostgresDriver.))
+(defn driver-init
+  []
+  (driver/register-driver! :postgres (PostgresDriver.)))

src/metabase/driver/sqlite.clj

@@ -137,4 +137,6 @@
           :string-length-fn          (constantly :LENGTH)
           :unix-timestamp->timestamp unix-timestamp->timestamp}))
 
-(driver/register-driver! :sqlite (SQLiteDriver.))
+(defn driver-init
+  []
+  (driver/register-driver! :sqlite (SQLiteDriver.)))

src/metabase/driver/sqlserver.clj

@@ -158,4 +158,6 @@
           :string-length-fn          (constantly :LEN)
           :unix-timestamp->timestamp unix-timestamp->timestamp}))
 
-(driver/register-driver! :sqlserver (SQLServerDriver.))
+(defn driver-init
+  []
+  (driver/register-driver! :sqlserver (SQLServerDriver.)))