apollo-caching-strategies

# Apollo Caching Strategies

Master Apollo Client's caching mechanisms for building performant applications
with optimal data fetching and state management strategies.

## Overview

Apollo Client's intelligent cache is a normalized, in-memory data store that
allows for efficient data fetching and updates. Understanding cache policies
and management strategies is crucial for building high-performance apps.

## Installation and Setup

### Cache Configuration

```javascript
// apollo/cache.js
import { InMemoryCache, makeVar } from '@apollo/client';

export const cache = new InMemoryCache({
  typePolicies: {
    Query: {
      fields: {
        posts: {
          // Pagination with offset
          keyArgs: ['filter'],
          merge(existing = [], incoming, { args }) {
            const merged = existing.slice(0);
            const offset = args?.offset || 0;

            for (let i = 0; i < incoming.length; i++) {
              merged[offset + i] = incoming[i];
            }

            return merged;
          }
        }
      }
    },
    Post: {
      keyFields: ['id'],
      fields: {
        comments: {
          merge(existing = [], incoming) {
            return [...existing, ...incoming];
          }
        }
      }
    },
    User: {
      keyFields: ['email'],
      fields: {
        fullName: {
          read(_, { readField }) {
            return `${readField('firstName')} ${readField('lastName')}`;
          }
        }
      }
    }
  }
});
```

## Core Patterns

### 1. Fetch Policies

```javascript
// Different fetch policies for different use cases
import { useQuery } from '@apollo/client';
import { GET_POSTS } from './queries';

// cache-first (default): Check cache first, network if not found
function CacheFirstPosts() {
  const { data } = useQuery(GET_POSTS, {
    fetchPolicy: 'cache-first'
  });
  return <PostsList posts={data?.posts} />;
}

// cache-only: Never make network request, cache or error
function CacheOnlyPosts() {
  const { data }