Merge pull request #438 from metabase/allow_unsetting_field_special_type

allow `Field.special_type` to be unset via API 

src/metabase/api/meta/field.clj

 (ns metabase.api.meta.field
   (:require [compojure.core :refer [GET PUT POST]]
-            [medley.core :as medley]
+            [medley.core :as m]
             [metabase.api.common :refer :all]
             [metabase.db :refer :all]
             [metabase.db.metadata-queries :as metadata]
@@ -36,14 +36,13 @@
 (defendpoint PUT "/:id"
   "Update `Field` with ID."
   [id :as {{:keys [field_type special_type preview_display description]} :body}]
-  {field_type FieldType
+  {field_type   FieldType
    special_type FieldSpecialType}
   (write-check Field id)
-  (check-500 (upd-non-nil-keys Field id
-               :field_type      field_type
-               :special_type    special_type
-               :preview_display preview_display
-               :description     description))
+  (check-500 (m/mapply upd Field id (merge {:description  description                                   ; you're allowed to unset description and special_type
+                                            :special_type special_type}                                 ; but field_type and preview_display must be replaced
+                                           (when field_type      {:field_type field_type})              ; with new non-nil values
+                                           (when preview_display {:preview_display preview_display}))))
   (sel :one Field :id id))
 
 (defendpoint GET "/:id/summary"

test/metabase/task_test.clj

@@ -67,16 +67,16 @@
          :restarted]
   [(do
      (stop-task-runner!)
-     (with-redefs [metabase.task/hourly-task-delay (constantly 50)
+     (with-redefs [metabase.task/hourly-task-delay (constantly 100)
                    metabase.task/hourly-tasks-hook mock-hourly-tasks-hook]
        (add-hook! #'hourly-tasks-hook inc-task-test-atom-counter-by-system-hour)
        (reset! task-test-atom-counter 0)
        (start-task-runner!)
 
        [@task-test-atom-counter      ; should be 0, since not enough time has elaspsed for the hook to be executed
-        (do (Thread/sleep 75)
-            @task-test-atom-counter) ; should have been called once (~25ms ago)
-        (do (Thread/sleep 100)
+        (do (Thread/sleep 150)
+            @task-test-atom-counter) ; should have been called once (~50ms ago)
+        (do (Thread/sleep 200)
             @task-test-atom-counter) ; should have been called two more times
         (do (stop-task-runner!)
             :stopped)]))