Subscriptions

What is a GraphQL Subscription

SubQuery now also supports Graphql Subscriptions. Like queries, subscriptions enable you to fetch data. Unlike queries, subscriptions are long-lasting operations that can change their result over time.

Subscriptions are very useful when you want your client application to change data or show some new data as soon as that change occurs or the new data is available. Subscriptions allow you to subscribe to your SubQuery project for changes.

Note Read more about [Subscriptions](https://www.apollographql.com/docs/react/data/subscriptions/). :::

How to Subscribe to an Entity

The basic example of a GraphQL subscription is to be notified when any new entities are created. In the following example, we subscribe to the Transfer entity and receive an update when there are any changes to this table.

You can create the subscription by querying the GraphQL endpoint as follows. Your connection will then subscribe to any changes made to the Transfer entity table.

subscription {
  transfer {
    id
    mutation_type
    _entity
  }
}

The body of the entity in your query indicates what data you want to receive via your subscription when the Transfer table is updated:

• id: Returns the ID of the entity that has changed.
• mutation_type: The action that has been made to this entity. Mutation types can be either INSERT, UPDATE or DELETE.
• _entity: the value of the entity itself in JSON format.

Filtering

We also support filter on subscriptions, which means a client should only receive updated subscription data if that data or mutation meets certain criteria.

There are two types of filters we are supporting:

• id : Filter to only return changes that affect a specific entity (designated by the ID).
• mutation_type: Only the same mutation type been made will return an update.

Assume we have an entity Balances, and it records the balance of each account.

type Balances {
  id: ID! # someone's account , eg. 15rb4HVycC1KLHsdaSdV1x2TJAmUkD7PhubmhL3PnGv7RiGY
  amount: Int! # the balance of this account
}

If we want to subscribe to any balance updates that affect a specific account, we can specify the subscription filter as follows:

subscription {
  balances(
    id: "15rb4HVycC1KLHsdaSdV1x2TJAmUkD7PhubmhL3PnGv7RiGY"
    mutation: UPDATE
  ) {
    id
    mutation_type
    _entity
  }
}

Note that the mutation filter can be one of INSERT, UPDATE or DELETE.

Important Please note that you must enable the `--subscription` flag on both the node and query service in order to use these functions. :::

Important

The subcription feature works on SubQuery's Managed Service when you directly call the listed GraphQL endpoint. It will not work within the in-browser GraphQL playground.