Update conflict in mongoose

Question

I'm having an issue with updating a user's count field in MongoDB using Mongoose. Here is my schema and the code I'm using:

const user=new Schema({
    username:String,
    count:{
        type:Number,
        default:()=>0
    }
},{
    optimisticConcurrency:true
});

async function helper(){

    //retriving user data from Db
    const user=await User.findOne({username:"ravi"});
    console.log(user);

    //updating using findoneAndUpdate
    await User.findOneAndUpdate({username:"ravi"},{$inc:{count:1}});
    
    
    //updating using save
    user.count+=1;
    const updatedUser=await user.save();
    console.log(updatedUser);

}

When I first update the user with findOneAndUpdate(), the count field is increased by 1. Then, when I update the user with save(), the count should increase by 1 again. The total count should be increased by 2, but it only increases by 1. How can I ensure the count field is updated correctly?

Answer 1

Because of this user local variable

const user= await User.findOne({username:"ravi"});
console.log(user); // count = 0 

You are getting user before findOneAndUpdate so count will be 0 initially. Then incrementing and save would give you 1 as count.

So you have to increment the local count value for findOneAndUpdate

async function helper(){

    //retriving user data from Db
    const user=await User.findOne({username:"ravi"});
    console.log(user);

    //updating using findoneAndUpdate and increment the local variable
    await User.findOneAndUpdate({username:"ravi"},{$inc:{count:1}}).then(()=> (++user.count));
    
    
    //updating using save
    user.count++;
    const updatedUser=await user.save();
    console.log(updatedUser);

}