Create or Update Sequelize

From the docs, you don’t need to query where to perform the update once you have the object. Also, the use of promise should simplify callbacks:

Implementation

function upsert(values, condition) {
    return Model
        .findOne({ where: condition })
        .then(function(obj) {
            // update
            if(obj)
                return obj.update(values);
            // insert
            return Model.create(values);
        })
}

Usage

upsert({ first_name: 'Taku' }, { id: 1234 }).then(function(result){
    res.status(200).send({success: true});
});

Note

1. This operation is not atomic.
2. Creates 2 network calls.

which means it is advisable to re-think the approach and probably just update values in one network call and either:

1. Look at the value returned (i.e. rows_affected) and decide what to do.
2. Return success if update operation succeeds. This is because whether the resource exists is not within this service’s responsibility.