الـ Transactions بـ node-postgres: كله أو ولا حاجة

import { pool, setup, balances } from "./db.js";

await setup();

// ❌ من غير transaction: خطوتين منفصلين
async function transfer(from, to, amount) {
  await pool.query("UPDATE accounts SET balance = balance + $1 WHERE id = $2", [amount, to]);
  await pool.query("UPDATE accounts SET balance = balance - $1 WHERE id = $2", [amount, from]);
}

try {
  await transfer(2, 1, 800); // عمر معاه 500 بس
} catch (err) {
  console.log("error:", err.message);
}
console.log(await balances());
await pool.end();

$ node main.js
error: new row for relation "accounts" violates check constraint "accounts_balance_check"
مُنى=1800 عمر=500 | المجموع=2300

import { pool, setup, balances } from "./db.js";

await setup();

// ❌ BEGIN على الـ pool: كل query ممكن تروح لـ connection مختلفة
async function transfer(from, to, amount) {
  await pool.query("BEGIN");
  try {
    await pool.query("UPDATE accounts SET balance = balance + $1 WHERE id = $2", [amount, to]);
    await pool.query("UPDATE accounts SET balance = balance - $1 WHERE id = $2", [amount, from]);
    await pool.query("COMMIT");
  } catch (err) {
    await pool.query("ROLLBACK");
    throw err;
  }
}

// 10 transfers مع بعض، زي server عليه requests كتير: نصهم هيفشل (عمر معاه 500 بس)
const jobs = Array.from({ length: 10 }, (_, i) => (i % 2 ? transfer(1, 2, 10) : transfer(2, 1, 800)));
const results = await Promise.allSettled(jobs);
console.log(results.map((r) => (r.status === "fulfilled" ? "✓" : "✗")).join(""));
console.log(await balances());
await pool.end();

$ node main.js
✗✓✗✓✗✓✗✓✗✓
مُنى=1770 عمر=510 | المجموع=2280

import { pool, setup, balances } from "./db.js";
import { withTransaction } from "./tx.js";

await setup();

function transfer(from, to, amount) {
  return withTransaction(async (c) => {
    await c.query("UPDATE accounts SET balance = balance + $1 WHERE id = $2", [amount, to]);
    await c.query("UPDATE accounts SET balance = balance - $1 WHERE id = $2", [amount, from]);
    await c.query("INSERT INTO transfers (from_id, to_id, amount) VALUES ($1, $2, $3)", [from, to, amount]);
  });
}

const jobs = Array.from({ length: 10 }, (_, i) => (i % 2 ? transfer(1, 2, 10) : transfer(2, 1, 800)));
const results = await Promise.allSettled(jobs);
console.log(results.map((r) => (r.status === "fulfilled" ? "✓" : "✗")).join(""));
console.log(await balances());
const { rows } = await pool.query("SELECT count(*) FROM transfers");
console.log("transfers:", rows[0].count, typeof rows[0].count);
await pool.end();

$ node main.js
✗✓✗✓✗✓✗✓✗✓
مُنى=950 عمر=550 | المجموع=1500
transfers: 5 string

import { pool, setup, balances } from "./db.js";
import { withTransaction } from "./tx.js";

await setup();
await pool.query("CREATE TABLE IF NOT EXISTS orders (id bigint GENERATED ALWAYS AS IDENTITY PRIMARY KEY, account_id bigint, total bigint)");


function checkout(accountId, items, coupon) {
  return withTransaction(async (c) => {
    const total = items.reduce((s, i) => s + i.price, 0);
    const { rows } = await c.query(
      "INSERT INTO orders (account_id, total) VALUES ($1, $2) RETURNING id",
      [accountId, total],
    );
    await c.query("UPDATE accounts SET balance = balance - $1 WHERE id = $2", [total, accountId]);
    if (coupon) {
      await c.query("SAVEPOINT coupon");
      try {
        await c.query("INSERT INTO coupons_used (code) VALUES ($1)", [coupon]);
      } catch {
        await c.query("ROLLBACK TO SAVEPOINT coupon");
      }
    }
    return { orderId: Number(rows[0].id), total };
  });
}

console.log(await checkout(1, [{ price: 300 }, { price: 200 }], "WELCOME"));
try {
  await checkout(2, [{ price: 900 }]);
} catch (err) {
  console.log("error:", err.message);
}
console.log(await balances());
const { rows } = await pool.query("SELECT count(*)::int AS n FROM orders");
console.log("orders:", rows[0].n);
await pool.end();

$ node main.js
{ orderId: 1, total: 500 }
error: new row for relation "accounts" violates check constraint "accounts_balance_check"
مُنى=500 عمر=500 | المجموع=1000
orders: 1

import { pool } from "./db.js";

// كل الـ queries على نفس الـ client، وأي error = ROLLBACK، والـ client يرجع للـ pool دايمًا
export async function withTransaction(fn) {
  const client = await pool.connect();
  try {
    await client.query("BEGIN");
    const result = await fn(client);
    await client.query("COMMIT");
    return result;
  } catch (err) {
    await client.query("ROLLBACK");
    throw err;
  } finally {
    client.release();
  }
}