Smart subscriptions plugin

This plugin provides a way of turning queries into GraphQL subscriptions. Each field, Object, and Interface in a schema can define subscriptions to be registered when that field or type is used in a smart subscription.

The basic flow of a smart subscription is:

Run the query the smart subscription is based on and push the initial result of that query to the subscription
As the query is resolved, register any subscriptions defined on fields or types that where used in the query
When any of the subscriptions are triggered, re-execute the query and push the updated data to the subscription.

There are additional options which will allow only the sub-tree of a field/type that triggered a fetch to re-resolved.

This pattern makes it easy to define subscriptions without having to worry about what parts of your schema are accessible via the subscribe query, since any type or field can register a subscription.

Usage

Install

npm install --save @pothos/plugin-smart-subscriptions

Setup

import SchemaBuilder from '@pothos/core';
import SmartSubscriptionsPlugin from '@pothos/plugin-smart-subscriptions';
 
const builder = new SchemaBuilder({
  plugins: [SmartSubscriptionsPlugin],
  smartSubscriptions: {
    debounceDelay: number | null;
    subscribe: (
      name: string,
      context: Context,
      cb: (err: unknown, data?: unknown) => void,
    ) => Promise<void> | void;
    unsubscribe: (name: string, context: Context) => Promise<void> | void;
  },
});

Helper for usage with async iterators

const builder = new SchemaBuilder({
  smartSubscriptions: {
    ...subscribeOptionsFromIterator((name, { pubsub }) => {
      return pubsub.asyncIterator(name);
    }),
  },
});

Creating a smart subscription

builder.queryFields((t) => ({
  polls: t.field({
    type: ['Poll'],
    smartSubscription: true,
    subscribe: (subscriptions, root, args, ctx, info) => {
      subscriptions.register('poll-added')
      subscriptions.register('poll-deleted')
    },
    resolve: (root, args, ctx, info) => {
      return ctx.getThings();
    },
  }),
})

Adding smartSubscription: true to a query field creates a field of the same name on the Subscriptions type. The subscribe option is optional, and shows how a field can register a subscription.

This would be queried as:

subscription {
  polls {
    question
    answers {
      id
      value
    }
  }
}

registering subscriptions for objects

builder.objectType('Poll', {
  subscribe: (subscriptions, poll, context) => {
    subscriptions.register(`poll/${poll.id}`)
  },
  fields: (t) => ({
    question: t.exposeString('question', {}),
    answers: t.field({...}),
  }),
});

This will create a new subscription for every Poll that is returned in the subscription. When the query is updated to fetch a new set of results because a subscription event fired, the subscribe call will be called again for each poll in the new result set.

more options

builder.objectType('Poll', {
  subscribe: (subscriptions, poll, context) => {
    subscriptions.register(`poll/${poll.id}`, {
      filter: (value) => true | false,
      invalidateCache: (value) => context.PollCache.remove(poll.id),
      refetch: ():  => context.Polls.fetchByID(poll.id)!),
    });
  },
  fields: (t) => ({
    ...
  }),
});

Passing a filter function will filter the events, any only cause a re-fetch if it returns true.

invalidateCache is called before refetching data, to allow any cache invalidation to happen so that when the new data is loaded, results are not stale.

refetch enables directly refetching the current object. When refetch is provided and a subscription event fires for the current object, or any of its children, other parts of the query that are not dependents of this object will no be refetched.

registering subscriptions for fields

builder.objectType('Poll', {
  fields: (t) => ({
    question: t.exposeString('question', {}),
    answers: t.field({
      type: ['Answer'],
      subscribe: (subscriptions, poll) => subscriptions.register(`poll-answers/${poll.id}`),
      resolve: (parent, args, context, info) => {
        return parent.answers;
      },
    }),
  }),
});

more options for fields

builder.objectType('Poll', {
  fields: (t) => ({
    question: t.exposeString('question', {}),
    answers: t.field({
      type: ['Answer'],
      canRefetch: true,
      subscribe: (subscriptions, poll) =>
        subscriptions.register(`poll-answers/${poll.id}`, {
          filter: (value) => true | false,
          invalidateCache: (value) => context.PollCache.remove(poll.id),
        }),
      resolve: (parent, args, context, info) => {
        return parent.answers;
      },
    }),
  }),
});

Similar to subscriptions on objects, fields can pass filter and invalidateCache functions when registering a subscription. Rather than passing a refetch function, you can set canRefetch to true in the field options. This will re-run the current resolve function to update it (and it's children) without having to re-run the rest of the query.

Known limitations

Currently value passed to filter and invalidateCache is typed as unknown. This should be improved in the future.
Does not work with list fields implemented with async-generators (used for @stream queries)

Smart subscriptions plugin

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