what does ref means mongooose

ref basically means that mongoose would store the ObjectId values and when you call populate using those ObjectIds would fetch and fill the documents for you. So in this case:

stories: [{ type: Schema.Types.ObjectId, ref: 'Story' }]

An ObjectId for the Story would be only stored in the Person stories array and when you call on populate('stories') mongoose would go and do another query to find and match all the ObjectId and return you the actual Stories objects.

So ref just tells mongoose that you want to store there a reference to another model and at some point you want to populate those and get the full blown model by that reference.

In a sense it is nothing more than a foreign key to another collection by which you fetch the actual document when populate is called.

Here is the code broken down:

Story.findOne({ title: 'Casino Royale' })  // <-- filter on title  // once a story is found populate its `author` with full author document   // instead of the `ObjectId` stored by the `ref`  .populate('author')  // execute the current pipeline  .exec(function (err, story) { // handle the resulting record    if (err) return handleError(err);      console.log('The author is %s', story.author.name);    });

Hope this helps.