This package implements transactions on top of node-postgres, based on this answer, but improved to remove a class of subtle bugs.
- No use-after-release bugs
- Automatic transactions-inside-transactions with savepoints
- Can be used with either
PoolorPoolClient
import tx from `pg-tx`
const pg = new Pool()
await tx(pg, async (db) => {
await db.query(`UPDATE accounts SET money = money - 50 WHERE name = 'bob'`)
await db.query(`UPDATE accounts SET money = money + 50 WHERE name = 'alice'`)
})
await tx(pg, async (db) => {
await db.query(`UPDATE accounts SET money = money - 50 WHERE name = 'bob'`)
await db.query(`UPDATE accounts SET money = money + 50 WHERE name = 'debbie'`)
// Any errors thrown inside the callback will terminate the transaction
throw new Error(`screw Debbie`)
})
// You can also use it with other packages that use Pool or PoolClient, like pgtyped
import { sql } from '@pgtyped/query'
const updateAccount = sql<IUpdateAccountQuery>`
UPDATE accounts
SET money = momey + $delta
WHERE name = $name
`
await tx(pg, async(db) => {
await udpateAccount.run({ name: 'bob', delta: -50 })
await udpateAccount.run({ name: 'charlie', delta: 50 })
})Naive approach to pg transactions, featured in this answer and used in many projects looks like this:
// DO NOT USE THIS CODE
export default async function tx<T>(
pg: Pool,
callback: (db: PoolClient) => Promise<T>
): Promise<T> {
const client = await pg.connect()
await client.query(`BEGIN`)
try {
const result = await callback(client)
await client.query(`COMMIT`)
return result
} catch (e) {
await client.query(`ROLLBACK`)
throw e
} finally {
client.release()
}
}However, this approach contains a subtle bug, because the client it passes to the callback stays valid after transaction finishes (successfully or not), and can be unknowingly used. In essence, it's a variation of use-after-free bug, but with database clients instead of memory.
Here's a demonstration of code that can trigger this condition:
async function failsQuickly(db: PoolClient) {
await db.query(`This query has an error`)
}
async function executesSlowly(db: PoolClient) {
// Takes a couple of seconds to complete
await externalApiCall()
// This operation will be executed OUTSIDE of transaction block!
await db.query(`
UPDATE external_api_calls
SET amount = amount + 1
WHERE service = 'some_service'
`)
}
await tx(pg, async (db) => {
await Promise.all([
failsQuickly(db),
executesSlowly(db)
])
})To prevent this, we use ProxyClient, which implements a disposable pattern. After the client has been released, any attempts to use it will throw an error.
To run tests, specify POSTGRES_URL in .env file like this:
POSTGRES_URL="postgres://postgres:password@127.0.0.1:5432/test-db"