如何在 mongoose 中重用 pre 中间件功能

Question

I need to reuse one of pre middleware functions in another pre middleware, for that I extracted a function like so:

async function encryptPassword(next) {
    if (!this.isModified('password')) {
        return next();
    }
    this.password = await bcrypt.hash(this.password, 5);
    this.passwordChangedAt = new Date();
    next();
}

UserSchema.pre('save', encryptPassword);

UserSchema.pre("findOneAndUpdate", encryptPassword);

But I am getting an error saying that this.isModified is not a function, I assume that this is referring to something else. How to fix this?

Answer 1

I dived into these pre/post hooks with a help of debugger & docs and I have found several things (these apply to both pre and post ):

Using save hook will mean that this refers a document itself. Thus, you can update its fields, call methods like isModified , etc. You should not have any issues with the above method.

However, findOneAndUpdate hook will mean that this refers to a query instead of document. And Query object will not have documents or their inherited methods (like isModified ).

I checked with debugger and can confirm it is the case (up-to-date with documentation).

A list of hooks:https://mongoosejs.com/docs/middleware.html#types-of-middleware

You will see that only the following hooks allow to modify documents:

validate
save
remove
updateOne
deleteOne
init (note: init hooks are synchronous)

And all others will not. It seems this is intentional ( https://github.com/Automattic/mongoose/issues/964 ).

To solve an issue with findOneAndUpdate , it seems the only way (most closely resembling) is to rework to findOne and updateOne as separate queries.