Managing Local State with Apollo

1. Introduction

This tutorial will take you through an in-depth look at managing local state with Apollo Client. Our main goal is to understand how Apollo Client can be used for state management in an HTML project.

You will learn:
- How to set up Apollo Client
- Ways to query and mutate local state using Apollo
- How to manage local state effectively

Prerequisites:
- Basic understanding of JavaScript and HTML
- Familiarity with GraphQL and state management concept is a plus

2. Step-by-Step Guide

Apollo Client is primarily used to interact with a GraphQL API. However, it can also manage local state, providing an all-in-one solution for data management.

Setup Apollo Client

First, you need to install the Apollo Client. You can do this using npm:

npm install @apollo/client graphql

After installing the package, you can setup Apollo Client as follows:

import { ApolloClient, InMemoryCache } from '@apollo/client';

const client = new ApolloClient({
  uri: 'http://localhost:4000/graphql',
  cache: new InMemoryCache()
});

Querying Local State

You can query the local state just like you would query a GraphQL API.

import { gql, useQuery } from '@apollo/client';

const GET_LOCAL_STATE = gql`
  query GetLocalState {
    localState @client
  }
`;

const { data, loading, error } = useQuery(GET_LOCAL_STATE);

Mutating Local State

You can also mutate the local state:

import { gql, useMutation } from '@apollo/client';

const UPDATE_LOCAL_STATE = gql`
  mutation UpdateLocalState($value: String!) {
    updateLocalState(value: $value) @client
  }
`;

const [updateLocalState] = useMutation(UPDATE_LOCAL_STATE);

3. Code Examples

Example: Querying Local State

Here is a practical example of querying local state:

import { gql, useQuery } from '@apollo/client';

const GET_LOCAL_STATE = gql`
  query GetLocalState {
    localState @client
  }
`;

function Component() {
  const { data, loading, error } = useQuery(GET_LOCAL_STATE);

  if (loading) return <p>Loading...</p>;
  if (error) return <p>Error :(</p>;

  return <h1>{data.localState}</h1>;
}

In the above code, we're using useQuery to fetch local state. The @client directive tells Apollo to fetch the data from the local cache.

Example: Mutating Local State

Here is an example of mutating local state:

import { gql, useMutation } from '@apollo/client';

const UPDATE_LOCAL_STATE = gql`
  mutation UpdateLocalState($value: String!) {
    updateLocalState(value: $value) @client
  }
`;

function Component() {
  const [updateLocalState] = useMutation(UPDATE_LOCAL_STATE);

  return (
    <button onClick={() => updateLocalState({ variables: { value: 'Updated!' } })}>
      Update State
    </button>
  );
}

In the above code, we're using useMutation to update the local state. Again, the @client directive tells Apollo to update the data in the local cache.

4. Summary

You've learned how to setup Apollo Client, query and mutate local state. You can use Apollo as a complete solution for data management in your applications, removing the need for other state management libraries.

Next Steps:
- Learn more about Apollo Client's advanced features
- Explore how to manage remote data with Apollo

Additional Resources:
- Apollo Client Documentation

5. Practice Exercises

Exercise 1: Create an Apollo Client instance and connect it to a local GraphQL server.

Exercise 2: Create a local state and query it using Apollo Client.

Exercise 3: Mutate the local state using Apollo Client.

Solutions:
- For Exercise 1, refer to the "Setting up Apollo Client" section.
- For Exercise 2 and 3, refer to the "Querying Local State" and "Mutating Local State" sections respectively.

Tips for further practice:
- Explore more complex queries and mutations
- Learn how to handle errors with Apollo Client
- Practice using Apollo Client with a real-world application.