Batch writes in Firebase - Step-by-Step Execution

Process Flow - Batch writes

Start Batch Write

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Add Write Operation 1

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Add Write Operation 2

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Commit Batch

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All Writes Applied Atomically

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End

Batch writes collect multiple write operations and apply them all at once atomically.

Execution Sample

Firebase

const batch = db.batch();
const doc1 = db.collection('users').doc('user1');
batch.set(doc1, {name: 'Alice'});
const doc2 = db.collection('users').doc('user2');
batch.update(doc2, {age: 30});
await batch.commit();

This code creates a batch, adds two write operations, then commits them together.

Process Table

Step	Action	Batch State	Result
1	Create batch object	Empty batch	Batch initialized
2	Add set operation for doc1	Batch with 1 write (set user1)	Operation queued
3	Add update operation for doc2	Batch with 2 writes (set user1, update user2)	Operation queued
4	Commit batch	Batch with 2 writes	Writes applied atomically
5	Batch cleared after commit	Empty batch	Ready for new writes

💡 Batch commit applies all writes atomically, then batch resets

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5
batch	undefined	1 write queued	2 writes queued	writes committed	empty batch

Key Moments - 3 Insights

Why do all writes happen at once and not one by one?

Because batch.commit() applies all queued writes atomically in one step, as shown in execution_table step 4.

What happens if one write in the batch fails?

The entire batch fails and no writes are applied, ensuring atomicity (all or nothing), as implied by the commit step in execution_table.

Can I reuse the batch object after commit?

No, after commit the batch is cleared (step 5), so you need to create a new batch for more writes.

Visual Quiz - 3 Questions

Look at the execution_table, what is the batch state after adding the second write?

A Empty batch

B Batch with 2 writes

C Batch with 1 write

D Writes committed

💡 Hint

Check execution_table row 3 under 'Batch State'

At which step does the batch apply all writes atomically?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look for 'Writes applied atomically' in execution_table

If you try to add a write after commit without creating a new batch, what happens?

A You must create a new batch first

B The batch is empty so write is queued normally

C The write is queued in the old batch

D The write is automatically committed

💡 Hint

Refer to variable_tracker and key_moments about batch state after commit

Concept Snapshot

Batch writes let you queue multiple write operations.
Use db.batch() to start.
Add writes with batch.set(), batch.update(), etc.
Call batch.commit() to apply all writes atomically.
Batch resets after commit; create new batch for more writes.

Full Transcript

Batch writes in Firebase let you group multiple write operations together. You start by creating a batch object. Then you add write operations like set or update to the batch. These writes are not applied immediately but queued. When you call commit on the batch, all writes are applied at once atomically, meaning either all succeed or none do. After commit, the batch is cleared and you need a new batch object for more writes. This ensures consistency and efficiency when updating multiple documents.