Why keep business logic out of Mongoose hooks?
Hooks are for data-related concerns (hashing, normalizing, logging). Business logic (emails, payments) in hooks becomes a tangled web that is hard to test and reason about. Put it in services or controllers instead.
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More FAQs in Mongoose Middleware: pre and post Hooks Explained
Middleware functions that run before or after operations like save, validate, update. pre('save') runs before writing; post('save') runs after. Useful for hashing, normalizing, logging, and side effects.
Use a pre('save') hook. Check if the password field is modified with this.isModified('passwordHash'). If yes, hash with bcrypt and set this.passwordHash. Call next() to continue. Skip hashing otherwise (e.g., profile updates).
Hooks use this to refer to the document being saved. Arrow functions do not bind this, so this would be undefined. Use regular functions (function(next) { ... }) instead.
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