Transactions

Transactions

Transactions ensure that a series of database operations either all succeed or all fail, maintaining data integrity. UQL provides several ways to handle transactions depending on your needs.

Functional Transactions

The functional approach is the most convenient way to run transactions. UQL handles the entire lifecycle automatically.

Using pool.transaction()

Obtains a fresh querier from the pool, runs the callback in a transaction, and releases automatically:

import { pool } from './uql.config.js';
import { User, Profile } from './shared/models/index.js';

const result = await pool.transaction(async (querier) => {
  const user = await querier.findOne(User, { $where: { email: '...' } });
  const profileId = await querier.insertOne(Profile, { userId: user.id, bio: '...' });
  return { userId: user.id, profileId };
});
// The querier is automatically released after the transaction

Using querier.transaction()

If you already have an active querier instance, you can use its transaction method for automatic commit/rollback:

const querier = await pool.getQuerier();

try {
  const result = await querier.transaction(async () => {
    const userId = await querier.insertOne(User, { name: '...' });
    await querier.insertOne(Profile, { userId, bio: '...' });
    return userId;
  });
} finally {
  await querier.release();
}

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Declarative Transactions

Perfect for NestJS and other Dependency Injection frameworks. Use @Transactional() to wrap a method and @InjectQuerier() to access the managed connection. UQL automatically handles the entire lifecycle: acquiring/starting the transaction, committing on success, rolling back on error, and releasing the connection.

import { Transactional, InjectQuerier, type Querier } from 'uql-orm';
import { User, Profile } from './shared/models/index.js';

export class UserService {
  @Transactional()
  async register(
    userData: Partial<User>,
    profileData: Partial<Profile>,
    @InjectQuerier()
    querier?: Querier
  ) {
    const userId = await querier.insertOne(User, userData);
    await querier.insertOne(Profile, { ...profileData, userId });
  }
}

You can specify an isolation level directly at the decorator level:

@Transactional({ isolationLevel: 'serializable' })
async transferFunds(
  fromId: string, toId: string, amount: number,
  @InjectQuerier() querier?: Querier
) {
  // runs under serializable isolation
}

Note

The @Transactional() decorator requires experimentalDecorators and emitDecoratorMetadata to be enabled in your tsconfig.json.

---

Imperative Transactions

For scenarios requiring granular control, you can manually manage the transaction lifecycle.

[!WARNING] When using manual transactions, always ensure queriers are released back to the pool, even in the event of an error.

import { pool } from './uql.config.js';
import { User, Profile } from './shared/models/index.js';

async function registerUser(userData: Partial<User>, profileData: Partial<Profile>) {
  const querier = await pool.getQuerier();

  try {
    await querier.beginTransaction();

    const userId = await querier.insertOne(User, userData);
    await querier.insertOne(Profile, { ...profileData, userId });

    await querier.commitTransaction();
  } catch (error) {
    await querier.rollbackTransaction();
    throw error;
  } finally {
    await querier.release();
  }
}

---

Isolation Levels

All transaction methods accept an optional TransactionOptions object to specify the isolation level. This controls the degree of visibility a transaction has to changes made by other concurrent transactions.

Supported Levels

Level	Description
read uncommitted	Allows dirty reads — can see uncommitted changes from other transactions.
read committed	Only sees data committed before the query began. Default for most databases.
repeatable read	Ensures repeated reads within the transaction return the same result.
serializable	Strictest level — transactions execute as if they were serial.

Usage

Pass isolationLevel in the options object to any transaction method:

// Functional — pool.transaction()
const result = await pool.transaction(async (querier) => {
  const account = await querier.findOne(Account, { $where: { id: accountId } });
  await querier.updateOneById(Account, accountId, {
    balance: account.balance - amount,
  });
  return account;
}, { isolationLevel: 'serializable' });

// Functional — querier.transaction()
await querier.transaction(async () => {
  // operations...
}, { isolationLevel: 'repeatable read' });

// Imperative
await querier.beginTransaction({ isolationLevel: 'read committed' });

Database Support

Database	Behavior
PostgreSQL	Full support — uses BEGIN TRANSACTION ISOLATION LEVEL ....
MySQL / MariaDB	Full support — uses SET TRANSACTION ISOLATION LEVEL before START TRANSACTION.
SQLite / LibSQL	Silently ignored (SQLite uses serializable by default).
MongoDB	Silently ignored.

Tip

The isolationLevel option is safely ignored on databases that don’t support it — your code remains portable across all supported databases without conditional logic.

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Nesting Behavior

When querier.transaction() or @Transactional() is called inside an existing transaction, UQL reuses the active transaction instead of starting a new one. This makes your code composable — a service method that uses querier.transaction() works correctly whether called standalone or from within another transaction.

const result = await pool.transaction(async (querier) => {
  await querier.insertOne(User, { name: 'Alice' });

  // This nested call reuses the outer transaction — no new BEGIN/COMMIT
  await querier.transaction(async () => {
    await querier.insertOne(Profile, { userId: 1, bio: '...' });
  });

  return querier.count(User, {});
});
// Both inserts are committed together by the outer transaction

If the inner callback throws, the error propagates to the outer transaction which rolls back everything — both outer and inner operations.

Note

beginTransaction() is the lowest-level API and does not support composable transactions — it throws TypeError('pending transaction') if called inside an existing transaction. Use querier.transaction() or @Transactional() for that use case.

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Transaction API Reference

Method	Lifecycle	Isolation Level	Nesting
pool.transaction(callback, opts?)	Automatic — acquires, commits/rollbacks, releases.	✅ via opts	Fresh querier
querier.transaction(callback, opts?)	Semi-Automatic — commits/rollbacks (caller releases).	✅ via opts	Reuses outer
querier.beginTransaction(opts?)	Manual — caller commits/rollbacks/releases.	✅ via opts	Throws
querier.commitTransaction()	Commits the active transaction.	—	—
querier.rollbackTransaction()	Rolls back the active transaction.	—	—
@Transactional({ isolationLevel? })	Automatic — full lifecycle via decorator.	✅ via options	Reuses outer