Transactions

Use transactions for business flows where partial success is unacceptable.

Contract

db.transaction<R>(fn: (tx: Database) => Promise<R>): Promise<R>

Inside the callback:

• all operations run in a single transaction
• any thrown error rolls back the full unit
• returned value becomes the transaction result

Canonical example

const transfer = await db.transaction(async (tx) => {
  await tx.wallets.update({ userId: fromId }, { balance: fromBalance - amount })
  await tx.wallets.update({ userId: toId }, { balance: toBalance + amount })
  const rows = await tx.transfers.insert({ fromId, toId, amount: String(amount) })
  return rows
})

Usage rules

• Use tx.* inside the callback, not outer db.*.
• Keep blocks short and database-focused.
• Do not call slow external services inside open transactions.
• Validate request payload before entering transaction().

Failure behavior

• Any thrown error causes rollback.
• Kadak rethrows the error for your service layer to handle.