adjust method

src/server/models/page-tag-relation.js

@@ -35,21 +35,19 @@ class PageTagRelation {
    * remove all invalid relations that has reference to unlinked document
    */
   static removeAllInvalidRelations() {
-    return this.find()
-      .then(relations => {
-        // filter invalid documents
-        return relations.filter(relation => {
-          return relation.relatedTag == null || relation.relatedPage == null;
-        });
-      })
-      .then(invalidRelations => {
-        const ids = invalidRelations.map(relation => relation._id);
-        return this.deleteMany({
-          _id: {
-            $in: ids
-          }
-        });
+    const self = this;
+    self.find(function(err, relations) {
+      // filter invalid documents
+      const invalidRelations = relations.filter(function(relation) {
+        return relation.relatedTag == null || relation.relatedPage == null;
       });
+      const ids = invalidRelations.map(relation => relation._id);
+      self.deleteMany({
+        _id: {
+          $in: ids
+        }
+      });
+    });
   }
 }