How can I retrieve an id from MongoDB create operation during a transaction? - mongodb

Question

I am trying to create an audit trail using Apollo Server and Mongoose. When a user initially registers, I create a document in the users collection and a document in the history collection for each piece of data they provided (username, password, email, etc) . For each history collection document, I include the id for the user document to create a relationship. Works perfectly.
However, when I add a transaction in (see below), the userId for the user document comes back as undefined, so I cannot add it to the history entry documents. I am assuming that the id for a document does not get created until the entire transaction has been completed?
Any ideas?
Mutation: {
register: async (_, { data }) => {
// Start a mongo session & transaction
const session = await mongoose.startSession()
session.startTransaction()
try {
// Hash password and create user
const hashedPassword = await bcrypt.hash(data.password, 12)
const user = await User.create(
[{ ...data, password: hashedPassword }],
{ session }
)
// Add history entries
HistoryEntry.create([
{
user: user.id,
action: 'registered'
},
{
user: user.id,
action: 'set',
object: 'profile',
instance: user.id,
property: 'firstName',
value: firstName
},
{
user: user.id,
action: 'set',
object: 'profile',
instance: user.id,
property: 'lastName',
value: lastName
},
{
user: user.id,
action: 'set',
object: 'profile',
instance: user.id,
property: 'password'
}
])
if (loginType === 'email') {
HistoryEntry.create({
user: user.id,
action: 'set',
object: 'profile',
instance: user.id,
property: 'email',
value: login
})
}
if (loginType === 'mobile') {
HistoryEntry.create({
user: user.id,
action: 'set',
object: 'profile',
instance: user.id,
property: 'mobile',
value: login
})
}
// commit the changes if everything was successful
await session.commitTransaction()
return {
ok: true,
user
}
} catch (err) {
// if anything fails above, rollback the changes in the transaction
await session.abortTransaction()
return formatErrors(err)
} finally {
// end the session
session.endSession()
}
}
}

Answer 1

If you think about it, how can you add a HistoryEntry if you haven't added User yet? It's not a 'history' as you are currently doing it. I believe you got two options here - set _id on User manually new Schema({ _id: { type: Schema.ObjectId, auto: true }}) and then generate it within the transaction: var userId = ObjectId(); and use for both User and History Entries.
And the second option, more semantically correct in this context, I believe - you should attach to post-save hook:
schema.post('save', function(doc) {
console.log('%s has been saved', doc._id);
});
So, whenever an User is created, a post-save hook is fired to update History.

Answer 2

Came across the same issue recently, hope you have figured it out already. I may add this for future seekers.
Following create function returns an array of created documents.
const user = await User.create(
[{ ...data, password: hashedPassword }],
{ session }
);
Therefore access the user id as user[0]._id
Pass the session also to HistoryEntry.create()
HistoryEntry.create([{...},{...}], {session})
Note: In this use case, I personally prefer #marek second option to use a post-save hook.