node.js - Push items into mongo array via mongoose

Question

I've scoured SO a good bit looking for the answer but I'm sure that I'm lost for the right words to describe what I'm after.

Basically I have a mongodb collection called 'people' The schema for that collection is as follows:

people: {
         name: String, 
         friends: [{firstName: String, lastName: String}]
        }

Now, I have a very basic express application that connects to the database and successfully creates 'people' with an empty friends array.

In a secondary place in the application, a form is in place to add friends. The form takes in firstName and lastName and then POSTs with the name field also for reference to the proper people object.

What I'm having a hard time doing is creating a new friend object and then "pushing" it into the friends array.

I know that when I do this via the mongo console I use the update function with $push as my second argument after the lookup criteria, but I can't seem to find the appropriate way to get mongoose to do this.

db.people.update({name: "John"}, {$push: {friends: {firstName: "Harry", lastName: "Potter"}}});

question from:https://stackoverflow.com/questions/65938008/how-to-push-new-values-to-existing-array-in-mongoose

Answer 1

Assuming, var friend = { firstName: 'Harry', lastName: 'Potter' };

There are two options you have:

Update the model in-memory, and save (plain javascript array.push):

person.friends.push(friend);
person.save(done);

or

PersonModel.update(
    { _id: person._id }, 
    { $push: { friends: friend } },
    done
);

I always try and go for the first option when possible, because it'll respect more of the benefits that mongoose gives you (hooks, validation, etc.).

However, if you are doing lots of concurrent writes, you will hit race conditions where you'll end up with nasty version errors to stop you from replacing the entire model each time and losing the previous friend you added. So only go to the former when it's absolutely necessary.