Introduction to Apollo Cache

Apollo Cache is a key component for managing local state in Apollo Client applications. It provides a robust and flexible way to manage local data and improve the performance of your app by avoiding unnecessary network requests.

Understanding Apollo Cache

Apollo Cache stores the result of queries and mutations, maintaining an in-memory cache to speed up data retrieval and reduce network usage.

Setting Up Apollo Cache

Before diving into the APIs, let’s set up Apollo Client with Apollo Cache:

 import { ApolloClient, InMemoryCache } from '@apollo/client';
const client = new ApolloClient({
  uri: 'https://your-api.com/graphql',
  cache: new InMemoryCache(),
}); 

Apollo Cache APIs

readQuery

The readQuery method allows you to read data from the cache synchronously.

 const data = client.cache.readQuery({
  query: YOUR_GRAPHQL_QUERY,
  variables: {
    id: '1',
  },
}); console.log(data); 

writeQuery

The writeQuery method allows you to write data directly into the cache.

 client.cache.writeQuery({
  query: YOUR_GRAPHQL_QUERY,
  data: { ...newData },
}); 

readFragment

The readFragment method allows you to read a fragment from the cache.

 const fragmentResult = client.cache.readFragment({
  id: 'Post:1',
  fragment: gql`
    fragment MyPostFragment on Post {
      id
      title
    }
  `,
}); console.log(fragmentResult); 

writeFragment

The writeFragment method allows you to write a fragment into the cache.

 client.cache.writeFragment({
  id: 'Post:1',
  fragment: gql`
    fragment MyPostFragment on Post {
      id
      title
    }
  `,
  data: {
    id: '1',
    title: 'Updated Title',
  },
}); 

evict

The evict method allows you to remove specific items from the cache.

 client.cache.evict({ id: 'Post:1' }); 

reset

The reset method allows you to reset the cache to an empty state.

 client.cache.reset(); 

Example Application Using Apollo Cache

Below is an example of an application that utilizes the above APIs:

 import React from 'react'; import { ApolloProvider, useQuery, gql } from '@apollo/client'; import { client } from './apolloClient';
const GET_ITEMS = gql`
  query GetItems {
    items {
      id
      name
    }
  }
`;
const ItemsList = () => {
  const { loading, error, data } = useQuery(GET_ITEMS);

  if (loading) return 
Loading...
;
  if (error) return 
Error :(
;

  return (
    

      {data.items.map(({ id, name }) => (
        
{name}
      ))}
    
  );
};
const App = () => (
  
    
Items
    
  
);
export default App; 

By using Apollo Cache effectively, you can enhance the performance of your Apollo Client applications and provide a smoother user experience.

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