Merge pull request #12677 from rdeavilafloqast/gh-12676

Fixing diffIndexes to cleanly return error instead of resulting in ty…

Author: vkarpov15

lib/model.js

@@ -1427,6 +1427,14 @@ Model.diffIndexes = function diffIndexes(options, callback) {
   return this.db.base._promiseOrCallback(callback, cb => {
     cb = this.$wrapCallback(cb);
     this.listIndexes((err, indexes) => {
+      if (err) {
+        // If the collection does not exist, it does not have indexes; safely proceed
+        if (err.codeName === 'NamespaceNotFound') {
+          indexes = [];
+        } else {
+          return cb(err, { toDrop, toCreate });
+        }
+      }
       const schemaIndexes = this.schema.indexes();
       // Iterate through the indexes created in mongodb and
       // compare against the indexes in the schema.

test/model.indexes.test.js

@@ -70,6 +70,15 @@ describe('model', function() {
       });
     });
 
+    it('should have schema-defined indexes in toCreate when calling diffIndexes on model with no documents (gh-12676)', () => {
+      const MySchema = new Schema({
+        name: { type: String, index: true }
+      });
+
+      const MyModel = db.model('my-model', MySchema); // This collection should not exist in DB; no documents
+      return MyModel.diffIndexes().then((res) => assert.deepEqual(res.toCreate[0], { name: 1 }));
+    });
+
     it('of embedded documents', function(done) {
       const BlogPosts = new Schema({
         _id: { type: ObjectId, index: true },