Fix syncing MongoDB tables with no database-type

src/metabase/sync/sync_metadata/fields/sync_metadata.clj

@@ -27,6 +27,7 @@
         {new-database-type :database-type
          new-base-type     :base-type
          new-field-comment :field-comment} field-metadata
+        new-database-type                  (or new-database-type "NULL")
         new-special-type                   (common/special-type field-metadata)
 
         new-db-type?

test/metabase/sync/sync_metadata/fields/sync_metadata_test.clj

+(ns metabase.sync.sync-metadata.fields.sync-metadata-test
+  (:require [expectations :refer [expect]]
+            [metabase.models.table :refer [Table]]
+            [metabase.sync.sync-metadata.fields.sync-metadata :as sync-metadata]
+            [toucan.db :as db]
+            [toucan.util.test :as tt]))
+
+(defn- updates-that-will-be-performed [new-metadata-from-sync metadata-in-application-db]
+  (tt/with-temp Table [table]
+    (let [update-operations (atom [])]
+      (with-redefs [db/update! (fn [model id updates]
+                                 (swap! update-operations conj [(name model) id updates]))]
+        (#'sync-metadata/update-field-metadata-if-needed!
+         table
+         new-metadata-from-sync
+         metadata-in-application-db)
+        @update-operations))))
+
+;; test that if database-type changes we will update it in the DB
+(expect
+  [["Field" 1 {:database_type "Integer"}]]
+  (updates-that-will-be-performed
+   {:name          "My Field"
+    :database-type "Integer"
+    :base-type     :type/Integer}
+   {:name          "My Field"
+    :database-type "NULL"
+    :base-type     :type/Integer
+    :id            1}))
+
+;; no changes should be made (i.e., no calls to `update!`) if nothing changes
+(expect
+ []
+ (updates-that-will-be-performed
+  {:name          "My Field"
+   :database-type "Integer"
+   :base-type     :type/Integer}
+  {:name          "My Field"
+   :database-type "Integer"
+   :base-type     :type/Integer
+   :id            1}))
+
+;; test that if `database-type` comes back as `nil` in the metadata from the sync process, we won't try to set a `nil`
+;; value in the DB -- this is against the rules -- we should set `NULL` instead. See `TableMetadataField` schema.
+(expect
+  [["Field" 1 {:database_type "NULL"}]]
+  (updates-that-will-be-performed
+   {:name          "My Field"
+    :database-type nil
+    :base-type     :type/Integer}
+   {:name          "My Field"
+    :database-type "Integer"
+    :base-type     :type/Integer
+    :id            1}))
+
+;; if `database-type` comes back as `nil` and was already saved in application DB as `NULL` no changes should be made
+(expect
+  []
+  (updates-that-will-be-performed
+   {:name          "My Field"
+    :database-type nil
+    :base-type     :type/Integer}
+   {:name          "My Field"
+    :database-type "NULL"
+    :base-type     :type/Integer
+    :id            1}))