Roles

Each #[field(..)] role turns on one behaviour of the queue: group, priority, partition key, retry_after, attempt, processed_at, lease, headers, payload.

A column that plays a role switches its behaviour on, and a table without it keeps the default:

Role	With the role	Without it
`group`	a subscription reads the group its name selects; a dead letter moves the row to another group	a subscription reads the whole table; a dead letter moves the row into another table
`group, fifo = true`	one row of a group is in work at a time, in claim order (FIFO)	the rows of a group run side by side
`priority`	a smaller value is claimed first	rows are claimed by `retry_after` where the table has it, then by id
`partition_key`	the delivery's partition key: under `workers_by_key(n)` the rows of one key run in order	the delivery has no key
`retry_after`	`retry_after(d)` hides the row for `d`	`retry_after(d)` returns the row at once, with a warning
`attempt`	`Ctx<keys::Attempt>` reads the count, and `max_attempts(n)` caps it	`Ctx<keys::Attempt>` reads `None`, and a mount with `max_attempts(n)` stops at startup
`processed_at`	acknowledgement marks the row	acknowledgement deletes the row
`locked_until`	the lease form	the row lock form, or the advisory lock form under `advisory_lock`
`headers`	the delivery's headers, kept in one column	the delivery's headers are empty
`payload`	payload mode: the handler takes the decoded payload	row mode: the handler takes the row

Every role but id is optional, and each plays on one column at most. generated beside a role marks a column the database fills in, such as a serial id or a column with a default, and the derive's insert leaves it out.

By hand, each role is a setter of InboxSpec. A role a delivery reads off the row also names its marker in type Table and implements a small trait: Payload and PayloadRow, Key and KeyRow, Attempt and AttemptRow, Headers and HeaderRow. The roles only the queue reads, such as group, priority and processed_at, need no field in the struct.

Example

The billing queue of a support table takes urgent tickets first, keeps each customer's tickets in order on one worker, and hides an open ticket for five minutes; an answered ticket stays in the table with its processed_at set.

Macros
Manual

examples/sqlx_tables_roles.rs
#[derive(Inbox, sqlx::FromRow)]
#[inbox(table = "support_tickets")]
struct Ticket {
    #[field(id, generated)]
    id: i64,
    #[field(group)]
    queue: String,
    #[field(priority)]
    urgency: i16,
    #[field(partition_key)]
    customer: String,
    #[field(retry_after)]
    retry_after: DateTime<Utc>,
    #[field(attempt, generated)]
    attempt: i16,
    #[field(processed_at)]
    processed_at: Option<DateTime<Utc>>,
    #[field(locked_until)]
    locked_until: Option<DateTime<Utc>>,
    #[field(payload)]
    payload: Vec<u8>,
}

#[subscriber(InboxQueue::<Ticket>::new("billing"))]
async fn triage(question: &Question) -> HandlerOutcome {
    if answer(question) {
        return HandlerOutcome::ack();
    }
    HandlerOutcome::retry_after(Duration::from_secs(300))
}

/// The service on the database `url` names.
fn service(url: &str) -> RustStream {
    let schema_url = url.to_owned();
    // Nothing connects here: the broker builds its pool when the service starts.
    let broker = SqlxBroker::from_url(url, SqlitePoolOptions::new());
    RustStream::new(AppInfo::new("support", "0.1.0"))
        // The table, created before the subscription checks it.
        .on_startup(async move |()| {
            let mut conn = SqliteConnection::connect(&schema_url).await?;
            sqlx::raw_sql(SCHEMA).execute(&mut conn).await?;
            conn.close().await
        })
        .with_broker(broker.route::<Ticket>("billing"), |b| {
            b.include(triage.workers_by_key(nonzero!(4)));
        })
}

examples/manual/sqlx_tables_roles.rs
#[derive(sqlx::FromRow)]
struct Ticket {
    id: i64,
    customer: String,
    attempt: i16,
    payload: Vec<u8>,
}

impl InboxTable for Ticket {
    type Id = i64;
    type Table = InboxSpec<(
        Key,
        RetryAfter<DateTime<Utc>>,
        Attempt,
        ProcessedAt<DateTime<Utc>>,
        Lease<DateTime<Utc>>,
        Payload,
    )>;
    const TABLE: Self::Table = InboxSpec::new("support_tickets", Column::new("id").generated())
        .group(Column::new("queue"))
        .priority(Column::new("urgency"))
        .partition_key(Column::new("customer"))
        .retry_after(Column::new("retry_after"))
        .attempt(Column::new("attempt").generated())
        .processed_at(Column::new("processed_at"))
        .lease(Column::new("locked_until"))
        .payload(Column::new("payload"));

    fn id(&self) -> &i64 {
        &self.id
    }
}

impl KeyRow for Ticket {
    type Key = String;

    fn partition_key(&self) -> &String {
        &self.customer
    }
}

impl AttemptRow for Ticket {
    type Attempt = i16;

    fn attempt(&self) -> &i16 {
        &self.attempt
    }
}

impl PayloadRow for Ticket {
    type Column = Vec<u8>;

    fn payload(&self) -> &[u8] {
        &self.payload
    }
}

struct Triage;

impl Handle<Question> for Triage {
    fn handle(
        &self,
        question: &Question,
        _outs: &(),
        _ctx: &mut Context<'_>,
    ) -> impl Future<Output = Result<(), HandlerOutcome>> {
        if answer(question) {
            return ready(Ok(()));
        }
        ready(Err(HandlerOutcome::retry_after(Duration::from_secs(300))))
    }
}

/// The service on the database `url` names.
fn service(url: &str) -> RustStream {
    let schema_url = url.to_owned();
    // Nothing connects here: the broker builds its pool when the service starts.
    let broker = SqlxBroker::from_url(url, SqlitePoolOptions::new());
    RustStream::new(AppInfo::new("support", "0.1.0"))
        // The table, created before the subscription checks it.
        .on_startup(async move |()| {
            let mut conn = SqliteConnection::connect(&schema_url).await?;
            sqlx::raw_sql(SCHEMA).execute(&mut conn).await?;
            conn.close().await
        })
        .with_broker(broker.route::<Ticket>("billing"), |b| {
            let triage = subscriber("billing", Triage)
                .map_source(|_| InboxQueue::<Ticket>::new("billing"))
                .workers_by_key(nonzero!(4));
            b.include(triage.build());
        })
}

Example​

Example