fix(model): allow bulkWrite upsert with empty update

Re: #8698

lib/helpers/model/castBulkWrite.js

@@ -44,6 +44,7 @@ module.exports = function castBulkWrite(model, op, options) {
           strict: model.schema.options.strict,
           overwrite: false
         });
+
         if (op['updateOne'].setDefaultsOnInsert) {
           setDefaultsOnInsert(op['updateOne']['filter'], model.schema, op['updateOne']['update'], {
             setDefaultsOnInsert: true,

lib/helpers/query/castUpdate.js

@@ -45,7 +45,6 @@ module.exports = function castUpdate(schema, obj, options, context, filter) {
   const ops = Object.keys(obj);
   let i = ops.length;
   const ret = {};
-  let hasKeys;
   let val;
   let hasDollarKey = false;
   const overwrite = options.overwrite;
@@ -81,12 +80,6 @@ module.exports = function castUpdate(schema, obj, options, context, filter) {
   // cast each value
   i = ops.length;
 
-  // if we get passed {} for the update, we still need to respect that when it
-  // is an overwrite scenario
-  if (overwrite) {
-    hasKeys = true;
-  }
-
   while (i--) {
     const op = ops[i];
     val = ret[op];
@@ -96,14 +89,8 @@ module.exports = function castUpdate(schema, obj, options, context, filter) {
         typeof val === 'object' &&
         !Buffer.isBuffer(val) &&
         (!overwrite || hasDollarKey)) {
-      hasKeys |= walkUpdatePath(schema, val, op, options, context, filter);
+      walkUpdatePath(schema, val, op, options, context, filter);
     } else if (overwrite && ret && typeof ret === 'object') {
-      // if we are just using overwrite, cast the query and then we will
-      // *always* return the value, even if it is an empty object. We need to
-      // set hasKeys above because we need to account for the case where the
-      // user passes {} and wants to clobber the whole document
-      // Also, _walkUpdatePath expects an operation, so give it $set since that
-      // is basically what we're doing
       walkUpdatePath(schema, ret, '$set', options, context, filter);
     } else {
       const msg = 'Invalid atomic update value for ' + op + '. '
@@ -116,7 +103,7 @@ module.exports = function castUpdate(schema, obj, options, context, filter) {
     }
   }
 
-  return hasKeys && ret;
+  return ret;
 };
 
 /*!

lib/query.js

@@ -3472,7 +3472,7 @@ Query.prototype._findAndModify = function(type, callback) {
     if (!isOverwriting) {
       this._update = castDoc(this, opts.overwrite);
       this._update = setDefaultsOnInsert(this._conditions, schema, this._update, opts);
-      if (!this._update) {
+      if (!this._update || Object.keys(this._update).length === 0) {
         if (opts.upsert) {
           // still need to do the upsert to empty doc
           const doc = utils.clone(castedQuery);

test/model.test.js

@@ -6474,4 +6474,26 @@ describe('Model', function() {
       assert.strictEqual(res.breed, 'Chorkie');
     });
   });
+
+  it('bulkWrite upsert works when update casts to empty (gh-8698)', function() {
+    const userSchema = new Schema({
+      name: String
+    });
+    const User = db.model('User', userSchema);
+    mongoose.set('debug', true)
+
+    return co(function*() {
+      yield User.bulkWrite([{
+        updateOne: {
+          filter: { name: 'test' },
+          update: { notInSchema: true },
+          upsert: true
+        }
+      }]);
+
+      const doc = yield User.findOne();
+      assert.ok(doc);
+      assert.strictEqual(doc.notInSchema, null);
+    });
+  });
 });

test/query.test.js

@@ -1645,14 +1645,6 @@ describe('Query', function() {
     assert.strictEqual(opts.maxTimeMS, 1000);
   });
 
-  describe('update', function() {
-    it('when empty, nothing is run', function(done) {
-      const q = new Query;
-      assert.equal(false, !!q._castUpdate({}));
-      done();
-    });
-  });
-
   describe('bug fixes', function() {
     describe('collations', function() {
       before(function(done) {