Transactions

A transaction groups multiple database operations so they either all succeed or all fail. Toasty supports interactive transactions on SQL databases (SQLite, PostgreSQL, MySQL).

Tip: If you just need multiple operations to execute atomically, consider using batch operations first. Batch operations are atomic and more efficient — they can be sent as a single statement, avoiding the extra round-trips that interactive transactions require (begin, execute, commit). Use interactive transactions when you need to read data and branch on the results within the same atomic scope.

Starting a transaction

Call db.transaction() to begin a transaction:

#![allow(unused)]
fn main() {
use toasty::{Model, Executor};
#[derive(Debug, toasty::Model)]
struct User {
    #[key]
    #[auto]
    id: u64,
    name: String,
}
async fn __example(mut db: toasty::Db) -> toasty::Result<()> {
let mut tx = db.transaction().await?;

toasty::create!(User { name: "Alice" }).exec(&mut tx).await?;
toasty::create!(User { name: "Bob" }).exec(&mut tx).await?;

tx.commit().await?;
Ok(())
}
}

The transaction borrows &mut Db, preventing other operations on the same Db handle while the transaction is open. Pass &mut tx to query builders the same way you pass &mut db.

The exclusive borrow is deliberate. Without it, it would be easy to run a statement against db while holding tx — that statement would execute on a separate connection pulled from the pool, bypassing the transaction entirely. The &mut keeps db unusable until the transaction ends, so every statement has to go through &mut tx.

If you genuinely need a second handle while a transaction is open — for example, an independent task doing unrelated work — clone the Db before starting the transaction:

let mut db2 = db.clone();
let mut tx = db.transaction().await?;

// `db2` is a separate handle backed by the same pool; use it freely
// for work that is not part of `tx`.

Clones share the underlying pool, so cloning is cheap and does not open a new connection.

The same rule applies to transactions started from a Connection and to nested transactions created from an existing Transaction: each takes &mut self so statements cannot accidentally bypass the innermost scope.

Running queries in a transaction

All the same operations work inside a transaction — creates, queries, updates, and deletes:

let mut tx = db.transaction().await?;

// Create
let user = toasty::create!(User { name: "Alice" }).exec(&mut tx).await?;

// Query
let users = User::all().exec(&mut tx).await?;

// Update
user.update().name("Bob").exec(&mut tx).await?;

// Delete
User::filter_by_id(user.id).delete().exec(&mut tx).await?;

tx.commit().await?;

Reads inside a transaction see the writes made earlier in the same transaction, even before commit:

let mut tx = db.transaction().await?;

toasty::create!(User { name: "Alice" }).exec(&mut tx).await?;

// This sees the record we just created
let users = User::all().exec(&mut tx).await?;
assert_eq!(users.len(), 1);

tx.commit().await?;

Commit and rollback

Call .commit() to save all changes made in the transaction:

let mut tx = db.transaction().await?;
toasty::create!(User { name: "Alice" }).exec(&mut tx).await?;
tx.commit().await?;

// The record is now visible outside the transaction
let users = User::all().exec(&mut db).await?;
assert_eq!(users.len(), 1);

Call .rollback() to discard all changes:

let mut tx = db.transaction().await?;
toasty::create!(User { name: "Alice" }).exec(&mut tx).await?;
tx.rollback().await?;

// The record was never persisted
let users = User::all().exec(&mut db).await?;
assert!(users.is_empty());

Auto-rollback on drop

If a transaction is dropped without calling .commit() or .rollback(), it automatically rolls back. This means you don’t need explicit rollback when an error occurs — just let the transaction go out of scope:

let mut tx = db.transaction().await?;
toasty::create!(User { name: "Alice" }).exec(&mut tx).await?;
// tx is dropped here without commit — changes are rolled back

This is useful in functions that return Result. If an operation inside the transaction fails with ?, the transaction is dropped and rolled back:

async fn transfer(db: &mut Db) -> toasty::Result<()> {
    let mut tx = db.transaction().await?;

    // If this fails, tx is dropped and rolled back
    let user = User::get_by_id(&mut tx, &1).await?;
    user.update().balance(user.balance - 100).exec(&mut tx).await?;

    let other = User::get_by_id(&mut tx, &2).await?;
    other.update().balance(other.balance + 100).exec(&mut tx).await?;

    tx.commit().await?;
    Ok(())
}

Nested transactions

Call .transaction() on an existing transaction to create a nested transaction. Nested transactions use database savepoints:

let mut tx = db.transaction().await?;
toasty::create!(User { name: "Alice" }).exec(&mut tx).await?;

{
    let mut nested = tx.transaction().await?;
    toasty::create!(User { name: "Bob" }).exec(&mut nested).await?;
    nested.commit().await?; // releases the savepoint
}

tx.commit().await?; // commits both Alice and Bob

Rolling back a nested transaction only undoes the work done inside it. The outer transaction continues:

let mut tx = db.transaction().await?;
toasty::create!(User { name: "Alice" }).exec(&mut tx).await?;

{
    let mut nested = tx.transaction().await?;
    toasty::create!(User { name: "Bob" }).exec(&mut nested).await?;
    nested.rollback().await?; // rolls back to savepoint — Bob is discarded
}

tx.commit().await?; // only Alice is committed

Nested transactions also auto-rollback on drop, just like top-level transactions.

Transaction options

Use transaction_builder() to configure a transaction before starting it:

use toasty::IsolationLevel;

let mut tx = db.transaction_builder()
    .isolation(IsolationLevel::Serializable)
    .read_only(true)
    .begin()
    .await?;

Isolation levels

Toasty supports four isolation levels:

Driver support varies. SQLite only supports Serializable. PostgreSQL and MySQL support all four levels.

Read-only transactions

Set .read_only(true) to create a read-only transaction. The database rejects write operations inside a read-only transaction.