Pass a Button value and Update the database - node.js

Question

Working on a personal project, one of the functions of the project is to update the user status on what event they are participating.
i wanted to submit a value using a button
<form action="/users/fooddrivebanner" method="POST"><button name="fooddrive" type="submit" value="fooddrive" id="fooddrive">Participate</button></form>
then pass the value to my route and save it inside my database
router.post('/fooddrivebanner', (req,res)=>{
const { fooddrive } = req.body;
const _id = ObjectId(req.session.passport.user._id);
User.findOne({ _id: _id }).then((user)=>{
if (!user) {
req.flash("error_msg", "user not found");
res.redirect("/fooddrivebanner");
}
if (typeof eventparticpating !== "undefined") {
user.eventparticpating = 'fooddrive';
}
user.save(function (err, resolve) {
if(err)
console.log('db error', err)
// saved!
});
})
.catch((err) => console.log(err));
Here is the User model
const mongoose = require('mongoose');
const UserSchema = new mongoose.Schema({
name: {
type: String,
required: true
},
email: {
type: String,
required: true
},
password: {
type: String,
required: true
},
date: {
type: Date,
default: Date.now
},
eventparticpating: {
type: String,
default: 'None At The Moment'
}
});
const User = mongoose.model('User', UserSchema);
module.exports = User;
It showed a console error
TypeError: Cannot set property 'eventparticpating' of null
UPDATE
Edit 1:
I followed Mr Gambino instructions, error Gone yet cannot update the database, how would i be able to adjust and find my user?

Answer 1

Instead of saving within the findOne function,you can do this:
router.post('/fooddrivebanner', async (req,res) => {
const { fooddrive } = req.body;
const _id = ObjectId(req.session.passport.user._id);
await User.findOne({ _id: _id }, (error, user) => {
if (error) {
req.flash("error_msg", "user not found");
res.redirect("/fooddrivebanner");
}
}).updateOne({ eventparticpating: "foodrive" });
});
I hope that answers your question