mongodb add item in array

Question

            await Cart.update(
              { $elemMatch: { user_id: decoded._id } },
              {
                $addToSet: {
                  "cart.&.items": {
                    product_id: req.query.product_id,
                    quantity: 1,
                  },
                },
              }
            );

My goal is to add elements to the array of items in the cart.

Answer 1

There's no syntax with & sign. MongoDB offers $ as a positional operator which allows you to modify existing item but you don't needed since you just want to append a new object to an array, try:

{
    $addToSet: {
        "cart.items": {
            product_id: req.query.product_id,
            quantity: 1,
        }
    }
}

Answer 2

            Cart.updateMany(
              { user_id: decoded._id },
              {
                $push: {
                  "cart.items": {
                    product_id: req.query.product_id,
                    quantity: 1,
                  },
                },
              }
            )

I finally found the right method through trial and error.