Watching data - Subscriptions

The GraphQL specification allows for something called subscriptions that are like GraphQL queries but instead of returning data in one read, you get data pushed from the server.

This is useful for your app to subscribe to "events" or "live results" from the backend, while also allowing you to control the "shape" of the event from your app.

GraphQL subscriptions are a critical component of adding realtime or reactive features to your apps easily. GraphQL clients and servers that support subscriptions are great because they allow you to build great experiences without having to deal with websocket code!

Make your first GraphQL subscription

1. Step 1: Head to https://hasura.io/learn/graphql/graphiql?tutorial=react-native
2. Step 2: Write this GraphQL query in the textarea:

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subscription {
  online_users {
    id
    last_seen
    user {
      name
    }
  }
}

3. Every time the set of online users change, you'll see the latest set on the response window on the right

How do GraphQL subscriptions work?

GraphQL queries and mutations are strings sent to a POST endpoint. What is a GraphQL subscription? That can't happen over a POST endpoint, because a simple HTTP endpoint would just return the response and the connection would close.

A GraphQL subscription is a subscription query string sent to a websocket endpoint. And whenever data changes on the backend, new data is pushed over websockets from the server to the client.

Summary

• You know how to make GraphQL subscriptions

Now that you're comfortable with the basics of using GraphQL, let's start integrating GraphQL APIs with an app!