lablup/relay-patterns

Relay Patterns for Backend.AI WebUI

Activation Triggers

• "Create a Relay query/fragment"
• "Add GraphQL data fetching"
• "Refetch pattern" or "fragment architecture"
• Working with useLazyLoadQuery, useFragment, useRefetchableFragment, usePaginationFragment
• Creating query orchestrator + fragment component pairs
• Questions about Relay naming conventions

Quick Reference

Commonly Used Hooks

• useLazyLoadQuery - Fetch data on component mount
• useFragment - Read fragment data from parent query
• useRefetchableFragment - Fragment with refetch capability
• usePaginationFragment - Fragment with pagination support

Naming Conventions

• Query fragments: prop name queryRef (type: ComponentQuery$key)
• Other types: prop name {typeName}Frgmt (e.g., userFrgmt: UserProfile_user$key)

Architecture Pattern

Query Orchestrator (useLazyLoadQuery, manages fetchKey/transitions)
  └── Fragment Component (useFragment, receives ref as prop, focused on presentation)

Detailed Patterns

Fragment Architecture

Separate data fetching (query orchestrator) from presentation (fragment component):

// Query Orchestrator Component
const UserManagement: React.FC = () => {
  const [fetchKey, updateFetchKey] = useUpdatableState('first');
  const [isPendingRefetch, startRefetchTransition] = useTransition();

  const { users } = useLazyLoadQuery<UserManagementQuery>(
    graphql`
      query UserManagementQuery {
        users {
          ...UserNodes_users
        }
      }
    `,
    {},
    { fetchPolicy: 'store-and-network', fetchKey },
  );

  return (
    <UserNodes
      usersFrgmt={users}
      loading={isPendingRefetch}
      onRefresh={() => {
        startRefetchTransition(() => {
          updateFetchKey();
        });
      }}
    />
  );
};

// Fragment Component
interface UserNodesProps {
  usersFrgmt: UserNodes_users$key;
  loading?: boolean;
  onRefresh?: () => void;
}

const UserNodes: React.FC<UserNodesProps> = ({
  usersFrgmt,
  loading,
  onRefresh,
}) => {
  const data = useFragment(
    graphql`
      fragment UserNodes_users on Query {
        users { id, email, username, is_active }
      }
    `,
    usersFrgmt,
  );

  return <BAITable dataSource={data.users} loading={loading} />;
};

Relay Hook Usage Examples

// useLazyLoadQuery
const data = useLazyLoadQuery(
  graphql`query MyQuery { user { id ...UserProfile_user } }`,
  {},
);

// useFragment
const data = useFragment(
  graphql`fragment UserProfile_user on User { id, name, email }`,
  userRef,
);

// useRefetchableFragment
const [data, refetch] = useRefetchableFragment(
  graphql`
    fragment UserList_users on Query
    @refetchable(queryName: "UserListRefetchQuery") {
      users { id, name }
    }
  `,
  usersRef,
);

Modern Relay Patterns

• @required directive - Type-safe null handling in fragments
• @alias directive - Rename fields for better semantics
• Suspense boundaries - Better loading state handling with concurrent features

Fragment Colocation

• Colocate GraphQL fragments with components that use them
• Use Relay's fragment composition for nested data requirements

Query Optimization

• Avoid over-fetching data - only request fields you need
• Use usePaginationFragment for lists
• Consider @defer and @stream for progressive loading

Client Directives

Backend.AI uses custom client-side directives to handle multi-version backend compatibility. These directives are defined in data/client-directives.graphql and processed at runtime by react/src/helper/graphql-transformer.ts before queries are sent to the server.

Directive Reference

| Directive | Purpose | When field is removed | |---|---|---| | @since(version: "X.Y.Z") | Field introduced in version X.Y.Z | Backend version < X.Y.Z | | @deprecatedSince(version: "X.Y.Z") | Field removed/replaced in version X.Y.Z | Backend version >= X.Y.Z | | @sinceMultiple(versions: [...]) | Multi-branch version support | Backend incompatible with version array | | @deprecatedSinceMultiple(versions: [...]) | Multi-branch deprecation | Backend compatible with version array | | @skipOnClient(if: $var) | Conditionally skip field at runtime | Variable evaluates to true |

Usage Patterns

# Field added in a specific version
query SessionDetailQuery {
  compute_session {
    name
    image
    permissions @since(version: "24.09.0")
    replicas @since(version: "24.12.0")
  }
}

# Field replaced in a newer version
fragment ImageInfo_image on ImageNode {
  name @deprecatedSince(version: "24.12.0")
  namespace @since(version: "24.12.0")
}

# Conditional field based on runtime feature flag
query UserSettingsQuery($isNotSupportTotp: Boolean!) {
  user {
    email
    totp_activated @skipOnClient(if: $isNotSupportTotp)
  }
}

How It Works

1. Directives are defined in data/client-directives.graphql and merged into the Relay schema via relay-base.config.js
2. At runtime, manipulateGraphQLQueryWithClientDirectives() in react/src/helper/graphql-transformer.ts strips incompatible fields before sending the query
3. The transformer also cleans up orphaned fragments and unused variables after field removal
4. Version comparison uses backendaiclient.isManagerVersionCompatibleWith() (PEP 440 semver)

Guidelines

• Always add @since when using fields introduced in newer backend versions
• Use @deprecatedSince + @since together when a field is replaced (old and new coexist)
• Prefer @skipOnClient over complex runtime conditionals for feature-flagged fields
• @sinceMultiple / @deprecatedSinceMultiple are for fields backported across version branches (rare)

Code Review Checklist

• [ ] Query orchestrator components separate from fragment components
• [ ] Fragment refs properly typed with generated $key types
• [ ] Fragment props follow naming conventions (queryRef / {typeName}Frgmt)
• [ ] @required directive used for non-null fields
• [ ] Fragments colocated with components that use them
• [ ] @since / @deprecatedSince used for version-dependent fields
• [ ] @skipOnClient used for feature-flagged fields instead of runtime conditionals