Transactions — Animate | AI Wisdom

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🎞 ANIMATE · Mode 3 of 5 · +100 XP— Database Transactions
📋BEGIN
⚙️Lock
🔄Execute
✅COMMIT
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Step 1 / 4
Speed
BEGIN Transaction
BEGIN starts a transaction — all following queries are isolated💡 Analogy
Like pressing "Lock" on a spreadsheet before editing — changes are staged, not live yet.
BEGIN starts a transaction block. All queries inside see a consistent database snapshot. Nothing commits until COMMIT.
Console Output
> BEGIN
> Transaction started
> Isolation: READ COMMITTED (default)
> All reads see committed data
●transactions.ts
BEGIN TransactionL11–12
1import { Pool } from 'pg';
2const pool = new Pool({ connectionString: process.env.DATABASE_URL });
3 
4// Bank transfer — must be atomic
5async function transferFunds(
6  fromId: string,
7  toId: string,
8  amount: number
9): Promise<void> {
10  const client = await pool.connect();
11  try {
12    await client.query('BEGIN');
13 
14    // Check sufficient balance (row-level lock with FOR UPDATE)
15    const { rows } = await client.query(
16      'SELECT balance FROM accounts WHERE id = $1 FOR UPDATE',
17      [fromId]
18    );
19    if (rows[0].balance < amount) {
20      throw new Error('Insufficient funds');
21    }
22 
23    // Debit source
24    await client.query(
25      'UPDATE accounts SET balance = balance - $1 WHERE id = $2',
26      [amount, fromId]
27    );
28 
29    // Credit destination
30    await client.query(
31      'UPDATE accounts SET balance = balance + $1 WHERE id = $2',
32      [amount, toId]
33    );
34 
35    // Log transaction
36    await client.query(
37      'INSERT INTO transfers (from_id, to_id, amount) VALUES ($1, $2, $3)',
38      [fromId, toId, amount]
39    );
40 
41    await client.query('COMMIT');
42  } catch (err) {
43    await client.query('ROLLBACK');
44    throw err;
45  } finally {
46    client.release();
47  }
48}
48 lines
Timeline — 4 Steps
BEGIN Transaction
BEGIN starts a transaction — all following queries are isolated💡 Analogy
Like pressing "Lock" on a spreadsheet before editing — changes are staged, not live yet.
BEGIN starts a transaction block. All queries inside see a consistent database snapshot. Nothing commits until COMMIT.
Console Output
> BEGIN
> Transaction started
> Isolation: READ COMMITTED (default)
> All reads see committed data

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Discussion

BEGIN starts a transaction — all following queries are isolated

💡 Analogy

Like pressing "Lock" on a spreadsheet before editing — changes are staged, not live yet.

BEGIN starts a transaction block. All queries inside see a consistent database snapshot. Nothing commits until COMMIT.

Console Output

> BEGIN
> Transaction started
> Isolation: READ COMMITTED (default)
> All reads see committed data

BEGIN starts a transaction — all following queries are isolated

💡 Analogy

Like pressing "Lock" on a spreadsheet before editing — changes are staged, not live yet.

BEGIN starts a transaction block. All queries inside see a consistent database snapshot. Nothing commits until COMMIT.

Console Output

> BEGIN
> Transaction started
> Isolation: READ COMMITTED (default)
> All reads see committed data