## Minimum requirements

| Package | Minimum version |
| --- | --- |
| controlplane | 0.88.3 |
| router | 0.88.0 |
| wgc | 0.55.0 |

## Full schema example

Here is a comprehensive example of how to use NATS with Cosmo Streams. This guide covers request, publish, subscribe directive. All examples can be modified to suit your specific needs. The schema directives and `edfs__*` types belong to the Cosmo Streams schema contract and must not be modified.

```
# Cosmo Streams

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

type edfs__PublishResult {
    success: Boolean!
}

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

# Custom

type Query {
    employeeFromEvent(id: Int!): Employee! @edfs__natsRequest(subject: "getEmployee.{{ args.id }}", providerId: "my-nats")
    employeeFromEventMyNats(employeeID: Int!): Employee! @edfs__natsRequest(subject: "getEmployeeMyNats.{{ args.employeeID }}", providerId: "my-nats")
}

input UpdateEmployeeInput {
    name: String
    email: String
}

type Mutation {
    updateEmployeeMyNats(employeeID: Int!, update: UpdateEmployeeInput!): edfs__PublishResult! @edfs__natsPublish(subject: "employeeUpdatedMyNats.{{ args.employeeID }}", providerId: "my-nats")
}

type Subscription {
    employeeUpdated(employeeID: Int!): Employee! @edfs__natsSubscribe(subjects: ["employeeUpdated.{{ args.employeeID }}"])
    employeeUpdatedMyNats(id: Int!): Employee! @edfs__natsSubscribe(subjects: ["employeeUpdatedMyNats.{{ args.id }}", "employeeUpdatedMyNatsTwo.{{ args.id }}"], providerId: "my-nats")
    employeeUpdatedNatsStream(id: Int!): Employee! @edfs__natsSubscribe(subjects: ["employeeUpdated.{{ args.id }}"], streamConfiguration: { consumerName: "consumerName", streamName: "streamName"}, providerId: "my-nats")
}

# Subgraph schema

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

You can create the Event-Driven Graph (EDG—an abstract subgraph) with the following command:

```
wgc subgraph publish edg --namespace default --schema edg.graphqls
```

## Router configuration

Based on the example above, you will need a compatible router configuration.

config.yaml

```
events:
  providers:
    nats:
      - id: my-nats
        url: "nats://localhost:4222"
        authentication:
          token: "token" # or
          user_info:
            username: "username"
            password: "password"
```

## Example Query

In the example query below, one or more subgraphs have been implemented alongside the Event-Driven Graph to resolve any other fields defined on `Employee`, e.g., `tag` and `details.surname`.Event-Driven Graphs (EDGs) do not define resolvers, and can only define fields that compose an entity’s primary key(s).

```
subscription {
  employeeUpdated(employeeID: 1) {
    id # resolved by the Event-Driven Graph (through the event)
    tag # resolved by another subgraph
    details { # resolved by another subgraph
      surname
    }
  }
}
```

## System diagram

NATS subscription flow from service to clients.