How to use GraphQL Code Generator with Apollo

GraphQL can improve app development speed, but to fully leverage its potential, a GraphQL Code Generator (codegen) is necessary. In this blog post, discover how to use GraphQL Code Generator to enhance GraphQL development with React, Apollo Client, and TypeScript. By generating Typed Queries, Mutations, and Subscriptions, GraphQL Code Generator ensures accurate typings and autocompletion for all queries, mutations, and subscription variables and results in your code. Let's begin.

Setup

Setting up GraphQL Code Generator only takes three easy steps:

1. Install the necessary npm packages.
2. Create a configuration file for the GraphQL Code Generator.
3. Include a script for the Code Generator in package.json.

Install NPM packages

Install the following npm packages required to run GraphQL Code Generator.

npm install graphql
npm install -D typescript @graphql-codegen/cli @graphql-codegen/client-preset @graphql-typed-document-node/core
# or yarn
yarn add graphql
yarn add -D typescript @graphql-codegen/cli @graphql-codegen/client-preset @graphql-typed-document-node/core
# or pnpm
pnpm add graphql
pnpm add -D typescript @graphql-codegen/cli @graphql-codegen/client-preset @graphql-typed-document-node/core

Create a Config File for GraphQL Code Generator

Next, create a codegen.ts configuration file next to your package.json file.

This configuration file contains information about:

• GraphQL API URL.
• GraphQL API headers.
• Where GraphQL queries and mutations exist in your code.

Update the file with your GraphQL endpoint and headers. Here's an example:

import { CodegenConfig } from '@graphql-codegen/cli'

const config: CodegenConfig = {
  schema: [
    {
      'http://localhost:1337/v1/graphql': {
        headers: {
          'x-hasura-admin-secret': 'nhost-admin-secret',
        },
      },
    },
  ],
  ignoreNoDocuments: true,
  generates: {
    './src/gql/': {
      documents: ['src/**/*.tsx'],
      preset: 'client',
      plugins: [],
    },
  },
}

export default config

This example configuration file is for a Nhost project using Hasura. We've set the GraphQL endpoint to http://localhost:1337/v1/graphql and added the x-hasura-admin-secret header so the GraphQL Code Generator can introspect the GraphQL API as an admin to get all queries and mutations available.

GraphQL autocomplete in VS Code

This step is optional but highly recommended.

You can get autocomplete when writing GraphQL queries and mutations in VS Code. This is another great way to improve your development workflow and reduce errors caused by typos.

To get inline autocomplete when you're writing GraphQL in VS Code, install the GraphQL for VSCode extension and add the following configuration (graphql.config.yaml) file next to your package.json file:

schema:
  - http://localhost:1337/v1/graphql:
      headers:
        x-hasura-admin-secret: nhost-admin-secret

Add a Codegen Script to package.json

As the last step, add a script to the package.json to run the GraphQL Code Generator.

{
  /*...*/
  "scripts": {
    /*...*/
    "codegen": "graphql-codegen"
  }
  /*...*/
}

You'll run this script (npm run codegen) every time you've changed anything in your GraphQL API or in your GraphQL files to get the most up-to-date types generated. You can also run the script in watch mode to automatically generate new types when you change your code using npm run codegen -w.

You've now completed the three configuration steps. It's time to start using the GraphQL Code Generator and unleash its power!

Workflow

As a mental model, this is how you will use the GraphQL Code Generator in your development workflow:

1. Run npm run codegen -w in watch mode to automatically generate types for queries, mutations, and subscriptions.
2. Write GraphQL queries and mutations and wrap the GraphQL code with the graphql() function.
3. Use the generated types to get autocompletion and type safety.

The graphql() function is generated by the GraphQL Code Generator and located at src/gql/gql.

Here's an example of how to write a GraphQL query and wrap it with the graphql() function:

import { graphql } from '../gql/gql'

const GET_TASKS = graphql(`
  query GetTasks {
    tasks(order_by: { createdAt: desc }) {
      id
      name
      done
    }
  }
`)

Example: Todo App

We'll now go through two examples of how to use the GraphQL Code Generator setup with Apollo Client in a Todo App. The first example is by using a query to fetch data and the other example is to use a mutation to modify data.

The full source code can be found on GitHub - GraphQL Code Generator Example with Apollo Client. This blog post contains a subset of the code to give you a basic understanding of how to use GraphQL Code Generator with Apollo Client.

For the two examples, we're using a table tasks in Hasura with three columns:

• id - UUID
• name - Text
• done - Boolean

App Setup

Install Apollo Client (@apollo/client). We'll also install @nhost/react and @nhost/react-apollo to get a pre-configured Apollo client and the NhostApolloProvider component to wrap our app as well as some helper functions for Nhost and React. If you're not using Nhost, you can configure your own Apollo client and Apollo Provider following Apollo's getting started guide.

npm install @apollo/client @nhost/react @nhost/react-apollo
# or yarn
yarn add @apollo/client @nhost/react @nhost/react-apollo
# or pnpm
pnpm add @apollo/client @nhost/react @nhost/react-apollo

Let's continue by first setting up the Apollo client in our app.

App

In App.tsx, we'll set up the Apollo client and wrap our app with the NhostApolloProvider component. Again, if you're not using Nhost, you can set up your own Apollo client and Apollo Provider.

import { NhostApolloProvider } from '@nhost/react-apollo'
import { NhostClient, NhostProvider } from '@nhost/react'

import { Tasks } from './components/Tasks'

const nhost = new NhostClient({
  subdomain: '<app-subdomain>',
  region: '<app-region>',
})

function App() {
  return (
    <NhostProvider nhost={nhost}>
      <NhostApolloProvider nhost={nhost}>
        <div>
          <div>Todo App</div>
          <Tasks />
        </div>
      </NhostApolloProvider>
    </NhostProvider>
  )
}

export default App

Get Tasks (GraphQL Query)

As we mentioned under the Workflow section above, we use the three-step process when using GraphQL Code Generator.

Just to repeat, these are the three steps:

1. Run npm run codegen -w in watch mode to automatically generate types for GraphQL queries, mutations, and subscriptions.
2. Write GraphQL queries and mutations and wrap the GraphQL code with the graphql() function.
3. Use the generated types to get autocompletion and type safety.

Let's get going.

Run the codegen to automatically generate types:

npm run codegen -w

Next, we'll combine the graphql() function with the useQuery() and GraphQL Request hook to fetch the data.

import { useMutation, useQuery } from '@apollo/client'

import { graphql } from '../gql/gql'

const GET_TASKS = graphql(`
  query GetTasks {
    tasks(order_by: { createdAt: desc }) {
      id
      name
      done
    }
  }
`)

export function Tasks() {
  const { data, loading, error } = useQuery(GET_TASKS)

  if (loading) {
    return <div>Loading...</div>
  }

  if (error) {
    console.error(error)
    return <div>Error</div>
  }

  if (!data) {
    return <div>No data</div>
  }

  const { tasks } = data

  return (
    <div>
      <h2>Todos</h2>
      <ul>
        {tasks.map((task) => (
          <li key={task.id}>{task.name}</li>
        ))}
      </ul>
    </div>
  )
}

That's it. In this scenario, using Nhost, you now have type-safety from Postgres, to GraphQL to TypeScript. From your database to your frontend. Good job!

Now, let's see some benefits of this setup!

If you're trying to access a property on tasks that does not exist, TypeScript will throw an error. E.g. if you're trying to access task.age.

src/components/Tasks.tsx:160:44 - error TS2339: Property 'age' does not exist on type '{ __typename?: "tasks" | undefined; id: any; name: string; done: boolean; }'.

160               <div className={style}>{task.age}</div>
                                               ~~~


Found 1 error in src/components/Tasks.tsx:160

NOTE: If you're using Vite remember that Vite does not perform type checking. You need to run tsc -noEmit to see any TypeScript errors.

If you're using VS Code you also see the TypeScript error while you're coding:

TypeScript also knows that task.name is of type string, which it has inferred from Postgres ( the task.name column is of type text) and GraphQL (task.name is of type String). This means you can't use task.name to perform arithmetic operations.

As you see, with the GraphQL Code Generator (and Postgres, GraphQL, and TypeScript) you're less likely to run into type errors. Overall, your application becomes more robust with fewer bugs.

Let's continue and see how to use GraphQL Code Generator with GraphQL mutations.

Insert Task (Mutation)

Specify the GraphQL mutation and wrap it around the graphql() function.

Next, specify the mutation in the useMutation hook. The mutationFn is the function that will be called when the mutation is triggered. If the mutation is successful, the onSuccess function will be called where we invalidate the tasks query to refetch the data.

Now you can use the insertTask function to trigger the mutation.

import { useState } from 'react'
import { useMutation, useQuery } from '@apollo/client'

import { graphql } from '../gql/gql'

const INSERT_TASK = graphql(`
  mutation InsertTask($task: tasks_insert_input!) {
    insertTasks(objects: [$task]) {
      affected_rows
      returning {
        id
        name
      }
    }
  }
`)

export function NewTask() {
  const [name, setName] = useState('')

  const [insertTask, { loading, error }] = useMutation(INSERT_TASK)

  const handleSubmit = async (e: React.FormEvent<HTMLFormElement>) => {
    e.preventDefault()

    if (!name) {
      return
    }

    try {
      await insertTask({
        variables: {
          task: {
            name,
          },
        },
        refetchQueries: ['GetTasks'],
      })
      setName('')
      alert('Task added!')
    } catch (error) {
      return console.error(error)
    }
  }

  return (
    <div>
      <h2>New Task</h2>
      <div>
        <form onSubmit={handleSubmit} className="space-y-4">
          <div>
            <label
              htmlFor="email"
              className="block text-sm font-medium text-gray-700"
            >
              Todo
            </label>
            <div className="mt-1">
              <input
                type="text"
                placeholder="Todo"
                value={name}
                onChange={(e) => setName(e.target.value)}
              />
            </div>
          </div>
          {error && <div>Error: {JSON.stringify(error, null, 2)}</div>}
          <div>
            <button type="submit" disabled={loading}>
              Add
            </button>
          </div>
        </form>
      </div>
    </div>
  )
}

GitHub Repository

The example code for this blog post is on GitHub - GraphQL Code Generator Example with Apollo Client.

Summary

That's it. You've now a basic understanding of how to set up and use GraphQL Code Generator with Apollo Client. This will help you build robust applications with fewer bugs. Good luck!

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