Apollo GraphQL Best Practices

You are an expert in Apollo Client, GraphQL, TypeScript, and React development. Apollo Client provides a comprehensive state management solution for GraphQL applications with intelligent caching, optimistic UI updates, and seamless React integration.

Core Principles

Use Apollo Client for state management and data fetching
Implement query components for data fetching
Utilize mutations for data modifications
Use fragments for reusable query parts
Implement proper error handling and loading states
Leverage TypeScript for type safety with GraphQL operations

Project Structure

src/
  components/
  graphql/
    queries/
      users.ts
      posts.ts
    mutations/
      users.ts
      posts.ts
    fragments/
      user.ts
      post.ts
  hooks/
    useUser.ts
    usePosts.ts
  pages/
  utils/
    apollo-client.ts
  types/
    generated/           # Generated TypeScript types

Setup and Configuration

Apollo Client Setup

typescript

// utils/apollo-client.ts
import { ApolloClient, InMemoryCache, HttpLink, from } from '@apollo/client';
import { onError } from '@apollo/client/link/error';

const httpLink = new HttpLink({
  uri: process.env.NEXT_PUBLIC_GRAPHQL_ENDPOINT,
});

const errorLink = onError(({ graphQLErrors, networkError }) => {
  if (graphQLErrors) {
    graphQLErrors.forEach(({ message, locations, path }) => {
      console.error(`[GraphQL error]: Message: ${message}, Path: ${path}`);
    });
  }
  if (networkError) {
    console.error(`[Network error]: ${networkError}`);
  }
});

export const apolloClient = new ApolloClient({
  link: from([errorLink, httpLink]),
  cache: new InMemoryCache({
    typePolicies: {
      Query: {
        fields: {
          users: {
            merge(existing = [], incoming) {
              return [...existing, ...incoming];
            },
          },
        },
      },
    },
  }),
  defaultOptions: {
    watchQuery: {
      fetchPolicy: 'cache-and-network',
      errorPolicy: 'all',
    },
    query: {
      fetchPolicy: 'cache-first',
      errorPolicy: 'all',
    },
    mutate: {
      errorPolicy: 'all',
    },
  },
});

Apollo Provider Setup

typescript

// pages/_app.tsx or app/providers.tsx
import { ApolloProvider } from '@apollo/client';
import { apolloClient } from '@/utils/apollo-client';

function App({ children }: { children: React.ReactNode }) {
  return (
    <ApolloProvider client={apolloClient}>
      {children}
    </ApolloProvider>
  );
}

Schema Design Best Practices

Naming Conventions

Use descriptive naming for types, fields, and arguments:

graphql

# Good
type User {
  id: ID!
  firstName: String!
  lastName: String!
  emailAddress: String!
  createdAt: DateTime!
}

type Query {
  getUserById(id: ID!): User
  getUsersByRole(role: UserRole!): [User!]!
}

# Avoid
type Query {
  getUser(id: ID!): User  # Less descriptive
}

Schema Structure

Define a clear schema reflecting your business domain:

graphql

type Query {
  user(id: ID!): User
  users(first: Int, after: String, filter: UserFilter): UserConnection!
}

type Mutation {
  createUser(input: CreateUserInput!): CreateUserPayload!
  updateUser(id: ID!, input: UpdateUserInput!): UpdateUserPayload!
  deleteUser(id: ID!): DeleteUserPayload!
}

input CreateUserInput {
  firstName: String!
  lastName: String!
  email: String!
}

type CreateUserPayload {
  user: User
  errors: [UserError!]
}

Query Patterns

Defining Queries with Fragments

typescript

// graphql/fragments/user.ts
import { gql } from '@apollo/client';

export const USER_FIELDS = gql`
  fragment UserFields on User {
    id
    firstName
    lastName
    email
    avatar
    createdAt
  }
`;

// graphql/queries/users.ts
import { gql } from '@apollo/client';
import { USER_FIELDS } from '../fragments/user';

export const GET_USER = gql`
  ${USER_FIELDS}
  query GetUser($id: ID!) {
    user(id: $id) {
      ...UserFields
    }
  }
`;

export const GET_USERS = gql`
  ${USER_FIELDS}
  query GetUsers($first: Int, $after: String) {
    users(first: $first, after: $after) {
      edges {
        node {
          ...UserFields
        }
        cursor
      }
      pageInfo {
        hasNextPage
        endCursor
      }
    }
  }
`;

Custom Query Hooks

typescript

// hooks/useUser.ts
import { useQuery, QueryHookOptions } from '@apollo/client';
import { GET_USER } from '@/graphql/queries/users';
import { User, GetUserQuery, GetUserQueryVariables } from '@/types/generated';

export function useUser(
  id: string,
  options?: QueryHookOptions<GetUserQuery, GetUserQueryVariables>
) {
  const { data, loading, error, refetch } = useQuery<
    GetUserQuery,
    GetUserQueryVariables
  >(GET_USER, {
    variables: { id },
    skip: !id,
    ...options,
  });

  return {
    user: data?.user,
    loading,
    error,
    refetch,
  };
}

Mutation Patterns

Defining Mutations

typescript

// graphql/mutations/users.ts
import { gql } from '@apollo/client';
import { USER_FIELDS } from '../fragments/user';

export const CREATE_USER = gql`
  ${USER_FIELDS}
  mutation CreateUser($input: CreateUserInput!) {
    createUser(input: $input) {
      user {
        ...UserFields
      }
      errors {
        field
        message
      }
    }
  }
`;

export const UPDATE_USER = gql`
  ${USER_FIELDS}
  mutation UpdateUser($id: ID!, $input: UpdateUserInput!) {
    updateUser(id: $id, input: $input) {
      user {
        ...UserFields
      }
      errors {
        field
        message
      }
    }
  }
`;

Custom Mutation Hooks

typescript

// hooks/useCreateUser.ts
import { useMutation, MutationHookOptions } from '@apollo/client';
import { CREATE_USER } from '@/graphql/mutations/users';
import { GET_USERS } from '@/graphql/queries/users';

export function useCreateUser(options?: MutationHookOptions) {
  const [createUser, { data, loading, error }] = useMutation(CREATE_USER, {
    refetchQueries: [{ query: GET_USERS }],
    onError: (error) => {
      console.error('Failed to create user:', error);
    },
    ...options,
  });

  return {
    createUser: (input: CreateUserInput) => createUser({ variables: { input } }),
    data,
    loading,
    error,
  };
}

Optimistic Updates

typescript

function useUpdateUser() {
  const [updateUser] = useMutation(UPDATE_USER, {
    optimisticResponse: ({ id, input }) => ({
      __typename: 'Mutation',
      updateUser: {
        __typename: 'UpdateUserPayload',
        user: {
          __typename: 'User',
          id,
          ...input,
        },
        errors: null,
      },
    }),
    update: (cache, { data }) => {
      const updatedUser = data?.updateUser?.user;
      if (updatedUser) {
        cache.modify({
          id: cache.identify(updatedUser),
          fields: {
            firstName: () => updatedUser.firstName,
            lastName: () => updatedUser.lastName,
          },
        });
      }
    },
  });

  return { updateUser };
}

Caching Strategies

Cache Normalization

typescript

const cache = new InMemoryCache({
  typePolicies: {
    User: {
      keyFields: ['id'],
    },
    Post: {
      keyFields: ['id'],
      fields: {
        author: {
          merge: true,
        },
      },
    },
  },
});

Reading and Writing Cache

typescript

// Read from cache
const user = client.readFragment({
  id: `User:${userId}`,
  fragment: USER_FIELDS,
});

// Write to cache
client.writeFragment({
  id: `User:${userId}`,
  fragment: USER_FIELDS,
  data: {
    ...user,
    firstName: 'Updated Name',
  },
});

Pagination

Cursor-Based Pagination (Relay Style)

Cursor-based pagination is recommended for large or rapidly changing data:

typescript

function useInfiniteUsers() {
  const { data, loading, fetchMore } = useQuery(GET_USERS, {
    variables: { first: 10 },
  });

  const loadMore = () => {
    if (!data?.users.pageInfo.hasNextPage) return;

    fetchMore({
      variables: {
        after: data.users.pageInfo.endCursor,
      },
    });
  };

  return {
    users: data?.users.edges.map((edge) => edge.node) ?? [],
    loading,
    hasMore: data?.users.pageInfo.hasNextPage ?? false,
    loadMore,
  };
}

Cache Merge Policy for Pagination

typescript

const cache = new InMemoryCache({
  typePolicies: {
    Query: {
      fields: {
        users: {
          keyArgs: ['filter'],
          merge(existing = { edges: [] }, incoming) {
            return {
              ...incoming,
              edges: [...existing.edges, ...incoming.edges],
            };
          },
        },
      },
    },
  },
});

Performance Optimization

DataLoader Pattern

Use batching techniques to reduce backend requests:

typescript

// Server-side with DataLoader
import DataLoader from 'dataloader';

const userLoader = new DataLoader(async (ids: string[]) => {
  const users = await db.users.findMany({ where: { id: { in: ids } } });
  return ids.map((id) => users.find((u) => u.id === id));
});

// In resolver
const resolvers = {
  Post: {
    author: (post) => userLoader.load(post.authorId),
  },
};

Query Batching

typescript

import { BatchHttpLink } from '@apollo/client/link/batch-http';

const batchLink = new BatchHttpLink({
  uri: '/graphql',
  batchMax: 10,
  batchInterval: 20,
});

Fetch Policies

typescript

// Network only - skip cache
useQuery(GET_USER, {
  fetchPolicy: 'network-only',
});

// Cache first - prefer cache
useQuery(GET_USER, {
  fetchPolicy: 'cache-first',
});

// Cache and network - return cache, then update
useQuery(GET_USER, {
  fetchPolicy: 'cache-and-network',
});

Error Handling

Query Error Handling

typescript

function UserProfile({ userId }: { userId: string }) {
  const { data, loading, error } = useUser(userId);

  if (loading) return <Skeleton />;

  if (error) {
    return (
      <ErrorMessage
        message="Failed to load user profile"
        retry={() => refetch()}
      />
    );
  }

  return <ProfileCard user={data} />;
}

Mutation Error Handling

typescript

function CreateUserForm() {
  const { createUser, loading, error } = useCreateUser({
    onCompleted: (data) => {
      if (data.createUser.errors?.length) {
        // Handle validation errors
        data.createUser.errors.forEach((err) => {
          setFieldError(err.field, err.message);
        });
      } else {
        // Success
        toast.success('User created successfully');
      }
    },
  });

  // ...
}

State Management

For simple state requirements, use Apollo Client's local state management:

typescript

// Define local-only fields
const typeDefs = gql`
  extend type Query {
    isLoggedIn: Boolean!
    cartItems: [CartItem!]!
  }
`;

// Read local state
const IS_LOGGED_IN = gql`
  query IsLoggedIn {
    isLoggedIn @client
  }
`;

// Write local state
client.writeQuery({
  query: IS_LOGGED_IN,
  data: { isLoggedIn: true },
});

For complex client-side state, consider using Zustand or Redux Toolkit alongside Apollo.

Anti-Patterns to Avoid

Over-fetching/Under-fetching: Only request fields you need
Chatty APIs: Minimize round trips with batching and DataLoader
God Objects: Avoid large, monolithic types with too many fields
Missing Error Handling: Always handle errors at query and mutation level
Ignoring Cache: Leverage Apollo's caching for performance
Not Using Fragments: Fragments improve reusability and maintainability
Skipping TypeScript: Generate types from your schema for type safety

Key Conventions

Use Apollo Provider at the root of your application
Implement custom hooks for Apollo operations
Use TypeScript for type safety with GraphQL operations (generate types)
Organize queries, mutations, and fragments in separate files
Use fragments for reusable query parts
Implement proper error handling and loading states
Use cursor-based pagination for large datasets
Leverage DataLoader for efficient data loading

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SKILL.md

Apollo GraphQL Best Practices

Core Principles

Project Structure

Setup and Configuration

Apollo Client Setup

Apollo Provider Setup

Schema Design Best Practices

Naming Conventions

Schema Structure

Query Patterns

Defining Queries with Fragments

Custom Query Hooks

Mutation Patterns

Defining Mutations

Custom Mutation Hooks

Optimistic Updates

Caching Strategies

Cache Normalization

Reading and Writing Cache

Pagination

Cursor-Based Pagination (Relay Style)

Cache Merge Policy for Pagination

Performance Optimization

DataLoader Pattern

Query Batching

Fetch Policies

Error Handling

Query Error Handling

Mutation Error Handling

State Management

Anti-Patterns to Avoid

Key Conventions