Why can't I close mongoose after this promise? - node.js

Question

I have a MongoDB instance to which I want to add entries, and I am using the mongoose library for this.
import mongoose from 'mongoose'
const personSchema = new mongoose.Schema({
name: String,
number: String
})
const Person = mongoose.model('Person', personSchema)
// addToPhonebook adds an entry to the phonebook
//
const addToPhonebook = (name, number) => {
const person = new Person({
name: name,
number: number
})
return person.save()
.then(_result => {
console.log(`added ${name} number ${number} to phonebook`)
mongoose.connection.close()
},
error => console.log(`nothing happened: ${error}`))
}
// Do some initialization
const url = 'mongodb+srv://...'
await mongoose.connect(url, {
useNewUrlParser: true,
useUnifiedTopology: true,
useFindAndModify: false,
useCreateIndex: true,
}).then(
_result => {
console.log('logged in to phonebook')
},
error => {
console.log(`couldn't log in to phonebook: ${error}`)
process.exit(2)
}
)
await addToPhonebook('Some name', '1-800-xxx-xxxx')
The code above works as expected. But, if I were to rearrange addToPhonebook such that mongoose.connection.close() is called after the first .then:
const addToPhonebook = (name, number) => {
const person = new Person({
name: name,
number: number
})
return person.save()
.then(_result => console.log(`added ${name} number ${number} to phonebook`),
error => console.log(`nothing happened: ${error}`))
.then(mongoose.connection.close())
}
It always returns nothing happened: MongoError: server is closed.
Am I doing something wrong or is my knowledge about promises faulty?

Answer 1

You're using your second .then() function wrong. You have to change it to this:
.then(() => mongoose.connection.close))
Explanation:
.then() needs a function as parameter. If you call the function just like this:
.then(mongoose.connection.close());
... you're passing the return value of .close() as parameter, therefore nothing happens.

Answer 2

mongoose.connection.close() is deprecated, check here use mongoose.disconnect().
I would suggest you not to close connection on every query, may be you need it at this moment, but try to make it more robust.
This stack overflow thread is good to check how to close connection i.e whenever your node process might end up or any other thing which might cause your application to restart.
const addToPhonebook = (name, number) => {
const person = new Person({
name: name,
number: number
})
return person.save()
.then(_result => console.log(`added ${name} number ${number} to phonebook`),
error => console.log(`nothing happened: ${error}`))
.then(mongoose.disconnect) // this will execute the method automatically
}