What is $set in MongoDB?

November 14, 2021

I am coding along with some MongoDB tutorial. I came across this.

const updatedUser = await User.findByIdAndUpdate(
      req.params.id,
      {
        $set: req.body,
      },
      { new: true }
    );

What exactly is $set? I think it is used to set anything from req.body to the DB, but I want to see some documentation about it and other $ use cases. However, I cannot find any documentation about $set.

>Solution :

The $set operator replaces the value of a field with the specified value.

This means that when u update some data, u can set the values of specific fields, even if those fields do not exist yet.

Here is all information u need: https://docs.mongodb.com/manual/reference/operator/update/set/

"If the field does not exist, $set will add a new field with the
specified value, provided that the new field does not violate a type
constraint. If you specify a dotted path for a non-existent field,
$set will create the embedded documents as needed to fulfill the
dotted path to the field."