# subscribe > Declares that a workflow state waits on an event, and configures the wait — who may hold it, who may hand it on, whether it is armed at all, and what must be satisfied first. A subscribe holds CONFIG only: the routes that fire when the event arrives live at the state level, and the SLA promises live in its own Assigned/Finished blocks. ## Summary {#summary} `subscribe` declares that a workflow state is listening for an event, and configures that wait — who may fill it, when it is armed, what must hold first, and what it promises. It is **config only**: the guarded routes that fire when the event arrives (`on Event when (…) { … goto … }`) live at the **state** level alongside the wait, not inside the `subscribe` block. ## Signature {#signature} ```osy syntax subscribe () [as ] [foreach ( in )] { Candidates = bool> | <() => List>; // who may HOLD or satisfy it Reassign = bool>; // who may hand it ON Assignee = ; // who it is handed to at arm time When = ; // whether it is armed on this run at all After = [, …]; // slots that must be satisfied first Assigned { … } // the pickup promise — Within, Remind, a breach arm Finished { … } // the completion promise Requires { … } // named preconditions on filling it } subscribe (); // bodyless — a wait with no configuration ``` ## Description {#description} A workflow state advances when an event it subscribes to arrives and a matching route transitions it. `subscribe` names that event and restates its typed parameters (so the payload is visible at the handler), then configures the wait itself. Each setting has its own page — see [See also](#see-also) — and the shape to hold is that they answer different questions: | setting | question | |---|---| | [`Candidates`](https://osysharp.com/reference/workflow/candidates/) | who may **hold or satisfy** this slot | | [`Reassign`](https://osysharp.com/reference/workflow/assign/) | who besides the holder may **move** it | | `Assignee` | who it belongs to from the moment it is armed (a slot with one is not a pool slot) | | `When` | whether this run gets the slot **at all** | | [`After`](https://osysharp.com/reference/workflow/slot-dependencies/) | which sibling slots must be satisfied before it opens | The **promises** — how long a slot may sit unclaimed, how long its holder has, the nudges along the way, the retries, and where a missed one routes — are declared in the [`Assigned`/`Finished`](https://osysharp.com/reference/workflow/milestone/) blocks inside the slot, not as flat settings on it. That is where `Within`, `Remind`, `Retries`, `Backoff` and the `Unassigned` / `Unfinished` / `Exhausted` arms live. A slot's **success** routes (`on when (…)`, `on (…)`) and the state's own timers (`on Expire`, `on Deadline`) live at the **state** level, not inside the `subscribe` — every `on …` in one place. An **entity-typed parameter is a live row, not a copy**. A route may read it and write through it, exactly as it can through the workflow's own tracked item, and those writes are saved with the rest of the transition: ```osy title="an event that carries the row it is about" syntax app=order-fulfillment event CustomerWithdrawsItem(OrderItem item); on CustomerWithdrawsItem(OrderItem item) { item.Status = ItemStatus.Withdrawn; // persisted with the transition RefundItem(item); } ``` The event's delivery context (who deposited, the claim) is available to a route that opts into a `Deposit` parameter — see workflow-route; it is never ambient. A state may hold more than one `subscribe` (multi-wait / N-of-M); that is its own surface — see workflow-multiwait. ## Examples {#examples} A pool slot the support team may take, a supervisor may move, and which promises to be picked up within an hour: ```osy title="a pool slot with a gate, a hand-over rule and a promise" syntax subscribe Respond() as Reply { Candidates = u => u.Team == Team.Support && u.OnDuty; Reassign = a => a.IsSupervisor; Assigned { Within = TimeSpan.FromHours(1); Unassigned { goto Escalated; } } } ``` The same wait as an app writes it, in context: ```osy title="a guarded approval wait" syntax sample=wf-approvals/model/po_approval.osy#draft-state state Draft { subscribe Submit(); on Submit { goto Review; } } ``` Minimal — a wait with no config, just the event: ```osy title="minimal" syntax app=order-fulfillment subscribe Submit(); ``` ## See also {#see-also} - [Candidates (slot)](https://osysharp.com/reference/workflow/candidates/) — the slot's `Candidates` gate: who may HOLD/satisfy this slot (predicate or computed set), and how a screen ASKS it before offering a button: `.For(item)..Candidates(u)` - [Assign — handing a slot to a named colleague](https://osysharp.com/reference/workflow/assign/) — `Reassign`, and the verbs that hand a slot to a named colleague - [Assigned / Finished (milestones)](https://osysharp.com/reference/workflow/milestone/) — the `Assigned`/`Finished` promises declared inside the slot: `Within`, `Remind`, `Retries`, `Backoff`, and the breach arms - [slot dependencies (After / When / Pending)](https://osysharp.com/reference/workflow/slot-dependencies/) — `After`: the sibling slots that must be satisfied before this one opens - [Requires — named preconditions, and the live checklist](https://osysharp.com/reference/workflow/requires/) — `Requires`: named preconditions on filling the slot, and the live checklist that reports them - workflow-event — the `event` this subscribes to (a method signature) - workflow-route — the state-level `on … goto …` routes that consume the deposit - workflow-state — the enclosing state and its `Expire` deadline - [Tracks and Initial (the field a workflow drives)](https://osysharp.com/reference/workflow/tracks/) — how the workflow binds to an entity's enum property