getting values from WriteResult mongo - mongodb

Question

I was trying to get familiar with the WriteResult object in mongo, but I can't access any of its values. The docs say the number of values inserted is stored in WriteResult.nInserted. Trying to access nInserted is crashing my server.
var readings = new Readings({
val1: parseInt(Data[0]),
val2: parseInt(Data[1]),
val3: parseInt(Data[2]),
val4: parseInt(Data[3]),
val5: parseInt(Data[4]),
val6: parseInt(Data[5]),
})
var result = readings.save(function (err, post){
if(err){return next(err)}
res.status(201).json(readings)
})
if(result.nInserted > 0){
console.log('wrote to database')
}
else{
console.log('could not write to database')
}
I know the data is being written to the database. I see it in the mongo shell.

Answer 1

The save method on a model instance doesn't return anything. All results are reported via the callback method, so you'd use something like this:
readings.save(function (err, doc, numberAffected){
if(err){return next(err)}
if (numberAffected > 0) {
console.log('updated an existing doc');
} else {
console.log('added a new doc');
}
res.status(201).json(doc)
})
Mongoose doesn't give you access to the full WriteResult, but as long as err is null you can rest assured the save succeeded and it's only a matter of whether an existing doc was updated or a new one was added. Because you're creating a new doc here, numberAffected will always be 0.