Context

import {FbInternalOnly, fbContent} from 'docusaurus-plugin-internaldocs-fb/internal'; import Tabs from '@theme/Tabs'; import TabItem from '@theme/TabItem';

In order to pass a service, or other values to be shared with all resolvers, the RelayModernStore provides a means of passing context. This gets passed to the third argument of all resolvers (live and non-live). This context argument analogous to the context argument used on the server which usually holds things like the database connection.

Setup

In order to pass context to live resolvers, pass a resolverContext argument to the initialization of RelayModernStore before creating the environment:

const store = new RelayModernStore(source, {
  resolverContext: {
    store: customStore,
  },
});

Usage in Resolvers

<Tabs groupId="resolver" defaultValue="JavaScript" values={fbContent({ internal: [ {label: 'JavaScript', value: 'JavaScript'}, {label: 'Flow', value: 'Flow'}, ], external: [ {label: 'JavaScript', value: 'JavaScript'}, {label: 'Flow', value: 'Flow'}, ] })}> <TabItem value="JavaScript">

The last argument in a resolver will contain the context type which contains the value passed into the store on initialization. If the resolver is on a model type or reads a @rootFragment, the context value will be the third argument. If the resolver is not on a model type and does not read a @rootFragment the context value will be passed as the thrid argument. Relay's generated artifacts will include generated type assertions to check that your resolver is typed correctly.

import type { LiveState } from 'relay-runtime';

/**
 * @RelayResolver Query.counter: Int
 * @live
 */
export function counter(
  _args,
  context
) {
  return {
    read: () => context.store.getState().counter,
    subscribe: (callback) => {
      return context.store.subscribe(callback);
    },
  };
}

Context is not currently supported in Flow

Type Checking

In order to ensure that the resolver is implemented with the correct types, pass a resolverContextType in the project config. This parameter expects a type name and a path to import from:

{
    "name": "project",
    "language": "flow",
    "resolverContextType": {
        "name": "IResolverContextType",
        "path": "path/to/file/IResolverContextType"
    }
}

To import from a package, use the following syntax for a package import:

{
    "name": "project",
    "language": "flow",
    "resolverContextType": {
        "name": "IResolverContextType",
        "package": "@package/name"
    }
}