- (with-transaction CONN THUNK [isolation: LEVEL] [access: MODE])procedure
Execute THUNK within a BEGIN TRANSACTION block, and return the value of thunk.
The transaction is committed if thunk returns a true value. If an exception occurs during thunk, or thunk returns #f, or the commit fails, the transaction will be rolled back. If this rollback fails, that is a critical error and you should likely abort.
However, escaping or re-entering the dynamic extent of thunk will not commit or rollback the in-progress transaction, so it is highly discouraged to jump out of a transaction. You will definitely run into trouble, unless you can ensure that no other statements will be executed on this connection until the outermost with-transaction returns normally.
If you provide LEVEL (which can be the symbol read-committed or serializable) this will set the transaction isolation mode for the transaction. If you provide MODE (which can be the symbol read/write or read-only) this will set the access mode for the transaction.
LEVEL is only allowed in the outermost transaction (when in-transaction? returns #f); if you provide it in an inner transaction, an error is raised. In subtransactions, MODE can only be "downgraded" to read-only from inside a read/write transaction, but you can't "upgrade" to read/write from a read-only transaction.