Setting with merge option in Firebase - Cheat Sheet & Quick Revision

Recall & Review

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What does the 'merge' option do when setting data in Firebase Firestore?

The 'merge' option updates only the specified fields in a document without deleting other existing fields. It merges new data with existing data.

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How do you use the 'merge' option in Firestore's set() method?

You pass an object with { merge: true } as the second argument to the set() method, like: set(data, { merge: true }).

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What happens if you set data without the merge option in Firestore?

The entire document is overwritten, and any fields not included in the new data are deleted.

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Why is using the merge option useful in real-life applications?

It lets you update only parts of a document, like changing a user's email without losing their profile info, similar to editing one part of a form without erasing the rest.

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Can the merge option be used to add new fields to an existing Firestore document?

Yes, merge allows adding new fields while keeping existing fields intact.

What does setting { merge: true } do in Firestore's set() method?

A Deletes the entire document

B Prevents any changes to the document

C Creates a new collection

D Updates only specified fields without deleting others

The merge option updates only the fields you specify, keeping other fields unchanged.

If you call set() without merge on an existing document, what happens?

A Document is overwritten completely

B Only specified fields update

C Document is deleted

D Nothing changes

Without merge, set() replaces the entire document with new data.

Which of these is a benefit of using merge when updating Firestore documents?

A It creates a backup copy

B It deletes old data automatically

C It merges new data with existing data

D It locks the document from changes

Merge combines new data with existing fields without deleting them.

How do you pass the merge option in Firestore's set() method?

A set(data, { merge: true })

B set(data, { overwrite: false })

C set(data, true)

D set(data, { update: true })

The merge option is passed as an object: { merge: true }.

Can merge option add new fields to an existing document?

A No, it only updates existing fields

B Yes, it adds new fields without removing old ones

C No, it deletes all fields first

D Yes, but only if the document is empty

Merge allows adding new fields while keeping existing fields intact.

Explain how the merge option affects updating a Firestore document.

Think about how you can change part of a document without losing the rest.

Describe a real-life scenario where using the merge option is helpful.

Imagine changing your email address but keeping your name and photo unchanged.