Add findOneAndUpdate to MongoCollection.

src/Adapters/Storage/Mongo/MongoCollection.js

@@ -46,7 +46,19 @@ export default class MongoCollection {
   count(query, { skip, limit, sort } = {}) {
     return this._mongoCollection.count(query, { skip, limit, sort });
   }
-  
+
+  // Atomically finds and updates an object based on query.
+  // The result is the promise with an object that was in the database !AFTER! changes.
+  // Postgres Note: Translates directly to `UPDATE * SET * ... RETURNING *`, which will return data after the change is done.
+  findOneAndUpdate(query, update) {
+    // arguments: query, sort, update, options(optional)
+    // Setting `new` option to true makes it return the after document, not the before one.
+    return this._mongoCollection.findAndModify(query, [], update, { new: true }).then(document => {
+      // Value is the object where mongo returns multiple fields.
+      return document.value;
+    })
+  }
+
   // Atomically find and delete an object based on query.
   // The result is the promise with an object that was in the database before deleting.
   // Postgres Note: Translates directly to `DELETE * FROM ... RETURNING *`, which will return data after delete is done.