# @onAssign

Legacy decorator that calls a method with the values at one or more string paths of the store, once all of them are defined. For new code, use [@handle](/docs/decorators/handle) with `{ waitForAllDefined: true }`: same behaviour, with typed `DataProviderKey` paths.

## Import

<sonic-code language="typescript">
  <template>
import { onAssign } from "@supersoniks/concorde/decorators";

@onAssign("passenger", "passengerSettings")
onReady(passenger: Passenger, settings: Settings) {}
  </template>
</sonic-code>

## Wait for every path

The method is called only when every path holds a value other than `null` or `undefined`, with the values in the order of the paths. After that, each assignment calls it again with the latest values. Subscriptions start after `connectedCallback` and stop in `disconnectedCallback`.

<sonic-code>
  <template>
    <docs-demo-sources for="demo-on-assign"></docs-demo-sources>
    <demo-on-assign></demo-on-assign>
  </template>
</sonic-code>

## Dynamic path

Paths accept `${prop}` placeholders resolved on the host. While a placeholder is `null` or `undefined`, that path is unsubscribed. Write the paths as plain strings, not template literals. Rules: [Dynamic path placeholders](/docs/misc/dynamic-path).

<sonic-code language="typescript">
  <template>
@property({ type: Number }) seat = 0;

@onAssign("passengers.${seat}", "passengerSettings.${seat}")
onSeat(passenger: Passenger, settings: Settings) {}
  </template>
</sonic-code>

## Migrate to @handle

<sonic-code language="typescript">
  <template>
// Before
@onAssign("passenger", "passengerSettings")
onReady(passenger: any, settings: any) {}

// After
const passengerKey = new DataProviderKey&lt;Passenger&gt;("passenger");
const settingsKey = new DataProviderKey&lt;Settings&gt;("passengerSettings");

@handle(passengerKey, settingsKey, { waitForAllDefined: true })
onReady(passenger: Passenger, settings: Settings) {}
  </template>
</sonic-code>

`@handle` accepts up to three keys. For more paths, keep `@onAssign` or split the logic into several `@handle` methods.

## API reference

| Argument | Type | Description |
|----------|------|-------------|
| `...paths` | `string[]` | Dot paths in the store (`"flights.0.status"`), optionally with `${prop}` placeholders; the method receives one argument per path, in order |