GraphQL is a powerful and flexible query language for APIs that allows clients to specify exactly what data they need. One of the lesser-known features of GraphQL is subscriptions, which allow for real-time updates to be pushed from the server to the client.
Here's an example of how you can set up a GraphQL subscription using the subscription
type in your schema:
type Subscription {
newMessage(roomId: ID!): Message!
@resolve(fn: "newMessageResolver")
}
type Message {
id: ID!
text: String!
room: Room!
}
type Room {
id: ID!
name: String!
}
In this example, the newMessage
subscription is defined as a field on the Subscription
type. It takes a single argument, roomId
, and returns a Message
type. The @resolve
directive is used to specify the function that will be used to resolve the subscription.
To actually subscribe to the newMessage
subscription, you can use a GraphQL client library, such as Apollo Client or Relay, to open a websocket connection to the server and send a subscription query. Here's an example using Apollo Client:
const subscription = gql`
subscription newMessage($roomId: ID!) {
newMessage(roomId: $roomId) {
id
text
room {
id
name
}
}
}
`;
const observer = client.subscribe({
query: subscription,
variables: { roomId: "123" }
});
observer.subscribe({
next: data => console.log(data)
});
With this code, the client will open a websocket connection to the server and subscribe to the newMessage
subscription, passing the roomId
variable as an argument. The server will push new messages to the client in real-time as they become available, and the next
callback will be called with the updated data.
In conclusion, GraphQL subscriptions allow for real-time updates to be pushed from the server to the client, making it easy to build dynamic and responsive web applications. Whether you're building a chat app, a real-time dashboard, or any other type of application that requires real-time updates, GraphQL subscriptions are a great tool to have in your toolbox.
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