Hasura trigger subscription server

Hasura trigger subscription server is a simple example of adding trigger event-based subscription support for hasura (see hasura/graphql-engine#2317 and hasura/graphql-engine#1355), using event triggers in hasura.

Overview

We use the following database schema:

scalar Timestamp
type Todo {
  id: ID!
  created_at: Timestamp!
  updated_at: Timestamp!
  content: String!
}

expose the following events in hasura console:

enum TodoEvent {
  on_todo_created
  on_todo_updated
  on_todo_deleted
}

and add a subscription in the custom subscription server:

type Subscription {
  todoSub(trigger: [TodoEvent]): Todo
}

Customization

This example implementation uses the following two endpoints at port 5000:

• /graphql: for exposing the graphql endpoint.
• /webhook: for listening to hasura event triggers.

Both endpoints can be configured in ./index.js

Add event-based subscription to an existing table

Say you added a new table tag to the database.

scalar Timestamp
type Todo {
  id: ID!
  created_at: Timestamp!
  updated_at: Timestamp!
  content: String!
  tags: [Tag]
}
type Tag {
  id: ID!
  text: String!
  todos: [Todo]
}

To add subscription to an existing table, you need to:

1. Add a trigger in hasura console (say if you want to get notified when tag get updated).

   • Click create in EVENTS tab in hasura console.
   • Add trigger named on_tag_updated.
   • choose table tag, trigger operations to update.
   • set webhook URL to http://localhost:5000/webhook, if you used the preset parameters in this repository.
   • Click Create Event Trigger

2. Add corresponding schema in ./schema.

   • Create a file called ./schema/tag.js.
   • Customize the typeDefs and resolvers in ./schema/tag.js. You can refer to ./schema/todo.js as a reference, or define your own logic.
   • Add tag schema to ./schema/index.js, in mergeSchemas function.

Todos

• [ ] This repo does not cover how to authenticate a user over websocket connection.
• [ ] This repo does not cover detailed information about how to filter a subscription with variables in resolvers.