Rendering Connections

import DocsRating from '@site/src/core/DocsRating'; import {OssOnly, FbInternalOnly} from 'docusaurus-plugin-internaldocs-fb/internal';

In Relay, in order to display a list of data that is backed by a GraphQL connection, first you need to declare a fragment that queries for a connection:

const {graphql} = require('RelayModern');

const userFragment = graphql`
  fragment UserFragment on User {
    name
    friends(after: $cursor, first: $count)
      @connection(key: "UserFragment_friends") {
      edges {
        node {
          ...FriendComponent
        }
      }
    }
  }
`;

• In the example above, we're querying for the friends field, which is a connection; in other words, it adheres to the connection spec. Specifically, we can query the edges and nodes in the connection; the edges usually contain information about the relationship between the entities, while the nodes are the actual entities at the other end of the relationship; in this case, the nodes are objects of type User representing the user's friends.
• In order to indicate to Relay that we want to perform pagination over this connection, we need to mark the field with the @connection directive. We must also provide a static unique identifier for this connection, known as the key. We recommend the following naming convention for the connection key: <fragment_name>_<field_name>.
• We will go into more detail later as to why it is necessary to mark the field as a @connection and give it a unique key in our Updating Connections section.

In order to render this fragment which queries for a connection, we can use the usePaginationFragment Hook:

import type {FriendsListComponent_user$key} from 'FriendsList_user.graphql';

const React = require('React');
const {Suspense} = require('React');

const {graphql, usePaginationFragment} = require('react-relay');

type Props = {
  user: FriendsListComponent_user$key,
};

function FriendsListComponent(props: Props) {
  const {data} = usePaginationFragment(
    graphql`
      fragment FriendsListComponent_user on User
      @refetchable(queryName: "FriendsListPaginationQuery") {
        name
        friends(first: $count, after: $cursor)
        @connection(key: "FriendsList_user_friends") {
          edges {
            node {
              ...FriendComponent
            }
          }
        }
      }
    `,
    props.user,
  );


  return (
    <>
      {data.name != null ? <h1>Friends of {data.name}:</h1> : null}

      <div>
        {(data.friends?.edges ?? []).map(edge => {
          const node = edge.node;
          return (
            <Suspense fallback={<Glimmer />}>
              <FriendComponent user={node} />
            </Suspense>
          );
        })}
      </div>
    </>
  );
}

module.exports = FriendsListComponent;

• usePaginationFragment behaves the same way as a useFragment (see the Fragments section), so our list of friends is available under data.friends.edges.node, as declared by the fragment. However, it also has a few additions:
  • It expects a fragment that is a connection field annotated with the @connection directive
  • It expects a fragment that is annotated with the @refetchable directive. Note that @refetchable directive can only be added to fragments that are "refetchable", that is, on fragments that are on Viewer, on Query, on any type that implements Node (i.e. a type that has an id field), or on a @fetchable type. <FbInternalOnly> For more info on @fetchable types, see this post. </FbInternalOnly>
• It takes two Flow type parameters: the type of the generated query (in our case FriendsListPaginationQuery), and a second type which can always be inferred, so you only need to pass underscore (_).