## NATS Server Configuration

Your NATS server must be configured to allow jetstreams before initiation. Please see [the documentation](https://docs.nats.io/nats-concepts/jetstream) for more details.

By configuring a stream and consumer, messages that are sent while a subscription is inactive can be consumed at a later time, e.g., when the subscription is restarted. This can help to prevent the loss of messages.

## Event-Driven Graph Schema Configuration

The `@edfs__natsSubscribe` directive defines an optional `streamConfiguration` argument. Providing this input object allows the configuration of a stream and consumer on a NATS connection. Note that if the `streamConfiguration` argument is undefined, the connection will be interpreted not to use a stream/consumer. If defined, all input object fields are required:

| Input Name                    | Type    | Value                                                                         |
| ----------------------------- | ------- | ----------------------------------------------------------------------------- |
| consumerInactiveThreshold     | Int!    | The inactive threshold of the consumer in seconds. The default value is 30 seconds. |
| consumerName                  | String! | The name of the consumer.                                                   |
| streamName                    | String! | The name of the stream.                                                    |

## NATS Configuration

### Stream

The stream name that is supplied to the `streamName` input must already be configured by your NATS server. If the relevant stream for a stream-reliant subscription cannot be found, an error will be returned. Please consult the following documentation on creating a stream (and ensure your NATS server has been configured to allow jetstreams): [https://docs.nats.io/nats-concepts/jetstream/streams](https://docs.nats.io/nats-concepts/jetstream/streams). Typically, this can be achieved using the [NATS CLI](https://docs.nats.io/using-nats/nats-tools/nats_cli) and following the prompts:

```
nats str add stream-name
```

### Consumer

As long as the stream exists, when a subscription is started, the router will attempt to identify an existing consumer. This identification is the name (supplied by the `consumerName` input), followed by a hash of the subjects, and the host name and listen address of the router. If a consumer is not found, the router will create a new durable consumer with the same name. By default, consumers will automatically be deleted after 30 seconds of inactivity. Inactivity is classed as the lack of a running subscription. You can change this value by specifying the value for the `consumerInactiveThreshold` input in the stream configuration. If you set the `consumerInactiveThreshold` to `0` (or any negative value), the consumer will never be deleted. If you wish for your consumer to have a timeout threshold, please configure accordingly using the following documentation: [https://docs.nats.io/nats-concepts/jetstream/consumers](https://docs.nats.io/nats-concepts/jetstream/consumers) [https://docs.nats.io/nats-concepts/jetstream/consumers/example_configuration](https://docs.nats.io/nats-concepts/jetstream/consumers/example_configuration). Typically, this can be achieved using the [NATS CLI](https://docs.nats.io/using-nats/nats-tools/nats_cli) and following the prompts:

```
nats consumer add stream-name consumer-name
```

## Example

In the example below, the NATS provider `my-nats` has also defined a stream configuration. The `streamName` input has been set to “myStream”, and the `consumerName` input has been set to `myConsumer`.

```
directive @edfs__natsSubscribe(
  subjects: [String!]!,
  providerId: String! = "default",
  streamConfiguration: edfs__NatsStreamConfiguration
) on FIELD_DEFINITION

input edfs__NatsStreamConfiguration {
    consumerInactiveThreshold: Int! = 30
    consumerName: String!
    streamName: String!
}

type Subscription {
    userUpdated(id: Int!): User! @edfs__natsSubscribe(
        subjects: ["user.{{ args.id }}"],
        providerId: "my-nats",
        streamConfiguration: { consumerName: "myConsumer", streamName: "myStream" },
    )
}

type User @key(fields: "id", resolvable: false) {
    id: Int! @external
}
```