#Hosi121/moondb_session

// acquire/release/close are callbacks for the caller's connection source.
let db = @sessions.database(acquire~, release~, close~, max_leases=4)
defer @async.protect_from_cancel(async fn() { db.close_and_wait() })
db.with_transaction((), async fn(tx) {
  let rows = tx.query("SELECT value FROM counters WHERE id = $1", params=[@moondb.Int(1)])
  ignore(tx.execute("UPDATE counters SET value = $1 WHERE id = $2",
    params=[@moondb.Int64(rows[0].int64(0) + 1L), @moondb.Int(1)]))
})

#Connection-source contract

• acquire: async () -> C, where C: AsyncDriver, transfers one exclusive connection. It must close any connection it cannot return, including on cancellation. It must not return a connection already owned by another scope.
• release: async (C, Bool) -> Unit takes ownership back. The boolean means discard: never put that connection back into service. It may already have been closed after a failed operation. A reusable source must rollback/reset session state before reusing a healthy connection, and retire it if reset fails.
• close: () -> Unit stops the source and wakes pending acquisition calls. Existing leases are released through the normal callback after their scopes end.

#Deliberate boundaries

• query and execute delegate separately and exactly once. run raises CombinedResultUnavailable; the upstream contract has no combined result.
• Value cases, row lookup, command metadata and errors are moondb's. In particular, its first-match duplicate-column lookup and its limited numeric value model are not silently changed. Prefer explicit column aliases.
• This adapter collects rows using upstream query; it adds no row/byte memory limit or streaming API. Use an appropriate driver or bounded SQL queries.
• It does not adopt the synchronous moondb.Pool for an async server, implement a wire protocol, or convert native unsigned/decimal values to Double.