Using Apollo Client’s Cache for Better Performance

When building modern React applications with GraphQL, optimizing performance is crucial for delivering a smooth user experience. One of the most powerful features of Apollo Client is its sophisticated caching system. Let’s dive into how you can leverage Apollo’s cache to supercharge your app’s performance.

Understanding Apollo Client’s Cache

At its core, Apollo Client maintains a normalized cache of your GraphQL data. Think of it as a local database in your browser that stores query results and manages data updates intelligently.

Key Strategies for Cache Optimization

1. Type Policies

Type policies are the building blocks of cache configuration. They tell Apollo Client how to handle specific types of data:

const cache = new InMemoryCache({
  typePolicies: {
    User: {
      fields: {
        fullName: {
          read(_, { readField }) {
            const firstName = readField('firstName');
            const lastName = readField('lastName');
            return `${firstName} ${lastName}`;
          }
        }
      }
    }
  }
});

2. Field Policies

Field policies help you customize how individual fields are stored and retrieved:

const cache = new InMemoryCache({
  typePolicies: {
    Query: {
      fields: {
        todos: {
          merge(existing = [], incoming) {
            return [...existing, ...incoming];
          }
        }
      }
    }
  }
});

3. Cache Redirects

Cache redirects are powerful tools for avoiding unnecessary network requests:

const cache = new InMemoryCache({
  typePolicies: {
    Query: {
      fields: {
        user: {
          read(_, { args, toReference }) {
            return toReference({
              __typename: 'User',
              id: args?.id,
            });
          }
        }
      }
    }
  }
});

Best Practices

1. Identify Cacheable Data: Not all data needs to be cached. Focus on frequently accessed data that doesn’t change often.

2. Configure Cache Retention: Use cache.gc() to clean up unused data and prevent memory bloat.

3. Implement Optimistic Updates: Enhance perceived performance by updating the UI before server response.

4. Monitor Cache Size: Keep an eye on your cache size to prevent memory issues in long-running applications.

Advanced Techniques

Fragment Matching

Fragments are excellent for cache optimization when dealing with interface types:

const cache = new InMemoryCache({
  possibleTypes: {
    Character: ['Human', 'Droid', 'Alien']
  }
});

Cache Persistence

Save your cache to localStorage for improved subsequent visits:

import { persistCache } from 'apollo3-cache-persist';

await persistCache({
  cache,
  storage: window.localStorage,
});

Remember that effective cache management is about finding the right balance between performance and data freshness. Regular testing and monitoring are essential to ensure your caching strategy aligns with your application’s needs.