Mongoose middleware (pre/post hooks) in Express - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Mongoose middleware (pre/post hooks)?

Mongoose middleware are functions that run before (pre) or after (post) certain Mongoose actions like saving or removing data. They let you add extra steps automatically.

beginner

When would you use a pre('save') hook in Mongoose?

Use a pre('save') hook to run code before saving a document, like hashing a password or validating data.

intermediate

What is the difference between pre and post hooks in Mongoose?

Pre hooks run before an action (like saving), so you can modify data or stop the action. Post hooks run after the action, useful for logging or cleanup.

intermediate

How do you define a post hook for the 'remove' action in Mongoose?

You add a post hook by calling schema.post('remove', function(doc) { /* code here */ }); This runs after a document is removed.

intermediate

Can Mongoose middleware hooks be asynchronous? How?

Yes, Mongoose middleware can be async by using async functions or calling next() after async work finishes. This helps wait for tasks like database calls.

Which Mongoose middleware hook runs before saving a document?

A pre('save')

B post('save')

C pre('remove')

D post('remove')

The pre('save') hook runs before a document is saved, allowing you to modify or validate data first.

What is a common use case for a post('save') hook?

A Hashing a password before saving

B Validating data before save

C Preventing save if invalid

D Logging that a document was saved

Post('save') hooks run after saving, so they are good for logging or triggering actions after data is stored.

How do you make a Mongoose middleware function asynchronous?

A Only use synchronous code

B Use async keyword or call next() after async work

C Return a promise without async keyword

D Use setTimeout inside the hook

You can define middleware as async functions or call next() after async tasks to handle asynchronous operations properly.

Which hook would you use to run code after a document is deleted?

A post('remove')

B pre('delete')

C pre('save')

D post('save')

The post('remove') hook runs after a document is removed from the database.

Can pre hooks prevent an action from completing?

A Yes, but only post hooks can do that

B No, pre hooks only run after the action

C Yes, by throwing an error or not calling next()

D No, hooks cannot affect actions

Pre hooks run before actions and can stop them by throwing errors or not calling next(), which halts the process.

Explain how Mongoose pre and post middleware hooks work and give an example use case for each.

Think about what you want to do before or after saving or deleting data.

Describe how to write an asynchronous pre-save hook in Mongoose and why you might need it.

Consider tasks that take time, like talking to other services or encrypting data.