Upsert behavior (update or insert) in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'upsert' mean in MongoDB?

Upsert means to update a document if it exists, or insert a new document if it does not exist.

beginner

Which MongoDB method supports upsert behavior?

The updateOne(), updateMany(), and findOneAndUpdate() methods support upsert when you set the option { upsert: true }.

beginner

What option must be set to true to enable upsert in an update operation?

The option 'upsert: true' must be set in the update operation options.

intermediate

If no document matches the filter in an upsert operation, what happens?

A new document is created using the filter and update fields combined, then inserted into the collection.

intermediate

Can upsert cause duplicate documents if the filter is not unique?

Yes, if the filter does not uniquely identify documents, multiple inserts can happen on repeated upserts.

What does setting { upsert: true } do in a MongoDB update operation?

A Only updates existing documents

B Deletes the matched document

C Inserts a new document if no match is found

D Returns an error if no document matches

Setting { upsert: true } inserts a new document if no existing document matches the filter.

Which method can perform an upsert in MongoDB?

A find()

B updateOne()

C deleteOne()

D insertOne()

updateOne() supports upsert when used with { upsert: true } option.

If a document matches the filter in an upsert operation, what happens?

A The document is updated

B A new document is inserted

C The document is deleted

D Nothing happens

If a document matches, it is updated according to the update instructions.

What happens if the filter in an upsert is not unique?

A The operation is ignored

B Only one document is updated

C An error is thrown

D Multiple documents may be inserted on repeated upserts

Non-unique filters can cause multiple inserts if no matching document is found.

Which option is required to perform an upsert with findOneAndUpdate()?

A { upsert: true }

B { multi: true }

C { new: true }

D { returnOriginal: true }

The { upsert: true } option enables upsert behavior in findOneAndUpdate().

Explain how upsert works in MongoDB and when you would use it.

Think about saving time by combining update and insert in one step.

Describe the risks of using upsert with a non-unique filter.

Consider what happens if MongoDB can't find a unique match.