Una guía para principiantes de GraphQL

Uno de los términos más discutidos hoy en día es API. Mucha gente no sabe exactamente qué es una API. Básicamente, API significa Interfaz de programación de aplicaciones. Es, como su nombre lo indica, una interfaz con la que las personas (desarrolladores, usuarios, consumidores) pueden interactuar con los datos.

Puedes pensar en una API como un bartender. Le pides un trago al barman y te dan lo que querías. Simple. Entonces, ¿por qué es eso un problema?

Desde el comienzo de la web moderna, la creación de API no ha sido tan difícil como parece. Pero aprender y comprender las API sí lo fue. Los desarrolladores forman la mayoría de las personas que usarán su API para crear algo o simplemente consumir datos. Por lo tanto, su API debe ser lo más limpia e intuitiva posible. Una API bien diseñada es muy fácil de usar y aprender. También es intuitivo, un buen punto a tener en cuenta cuando empiece a diseñar su API.

Hemos estado utilizando REST para crear API durante mucho tiempo. Junto con eso vienen algunos problemas. Al construir una API usando el diseño REST, enfrentará algunos problemas como:

1) tendrás muchos puntos finales

2) será mucho más difícil para los desarrolladores aprender y comprender su API

3) hay una búsqueda de información excesiva o insuficiente

Para resolver estos problemas, Facebook creó GraphQL. Hoy en día, creo que GraphQL es la mejor forma de crear API. Este artículo le dirá por qué debería comenzar a aprenderlo hoy.

En este artículo, aprenderá cómo funciona GraphQL. Le mostraré cómo crear una API potente, eficiente y muy bien diseñada utilizando GraphQL.

Probablemente ya haya oído hablar de GraphQL, ya que muchas personas y empresas lo están utilizando. Dado que GraphQL es de código abierto, su comunidad ha crecido enormemente.

Ahora es el momento de que empiece a aprender en la práctica cómo funciona GraphQL y todo sobre su magia.

¿Qué es GraphQL?

GraphQL es un lenguaje de consulta de código abierto desarrollado por Facebook. Nos proporciona una forma más eficiente de diseñar, crear y consumir nuestras API. Básicamente, es el reemplazo de REST.

GraphQL tiene muchas características, como:

  1. Escribe los datos que desea y obtiene exactamente los datos que desea. No más recaudación excesiva de información como estamos acostumbrados con REST.
  2. Nos da un único punto final , no más versión 2 o versión 3 para la misma API.
  3. GraphQL está fuertemente tipado , y con eso puede validar una consulta dentro del sistema de tipos GraphQL antes de la ejecución. Nos ayuda a crear API más potentes.

Esta es una introducción básica a GraphQL: por qué es tan poderoso y por qué está ganando mucha popularidad en estos días. Si desea obtener más información al respecto, le recomiendo que visite el sitio web GraphQL y lo revise.

Empezando

El objetivo principal de este artículo no es aprender a configurar un servidor GraphQL, por lo que no vamos a profundizar en eso por ahora. El objetivo es aprender cómo funciona GraphQL en la práctica, por lo que usaremos un servidor GraphQL de configuración cero llamado ☄️ Graphpack.

Para comenzar nuestro proyecto, vamos a crear una nueva carpeta y puedes nombrarla como quieras. Lo voy a nombrar graphql-server:

Abra su terminal y escriba:

mkdir graphql-server

Ahora, debe tener npm o hilo instalado en su máquina. Si no sabe cuáles son, npm y yarn son administradores de paquetes para el lenguaje de programación JavaScript. Para Node.js, el administrador de paquetes predeterminado es npm .

Dentro de su carpeta creada, escriba el siguiente comando:

npm init -y

O si usa hilo:

yarn init 

npm creará un package.jsonarchivo para usted, y todas las dependencias que instaló y sus comandos estarán allí.

Así que ahora vamos a instalar la única dependencia que vamos a usar.

☄️Graphpack le permite crear un servidor GraphQL sin configuración . Como recién estamos comenzando con GraphQL, esto nos ayudará mucho a continuar y aprender más sin preocuparnos por la configuración del servidor.

En su terminal, dentro de su carpeta raíz, instálelo así:

npm install --save-dev graphpack

O, si usa hilo, debería hacerlo así:

yarn add --dev graphpack

Después de instalar Graphpack, vaya a nuestros scripts en el package.jsonarchivo y coloque el siguiente código allí:

"scripts": { "dev": "graphpack", "build": "graphpack build" }

Vamos a crear una carpeta llamada src, y será la única carpeta en todo nuestro servidor.

Cree una carpeta llamada src, después de eso, dentro de nuestra carpeta, crearemos solo tres archivos.

Dentro de nuestra srccarpeta creamos un archivo llamado schema.graphql. Dentro de este primer archivo, ponga el siguiente código:

type Query { hello: String }

En este schema.graphqlarchivo estará todo nuestro esquema GraphQL. Si no sabe qué es, se lo explicaré más tarde, no se preocupe.

Ahora, dentro de nuestra srccarpeta, cree un segundo archivo. Llámalo resolvers.jsy, dentro de este segundo archivo, coloca el siguiente código:

import { users } from "./db"; const resolvers = { Query: { hello: () => "Hello World!" } }; export default resolvers;

Este resolvers.jsarchivo será la forma en que proporcionamos las instrucciones para convertir una operación GraphQL en datos.

Y finalmente, dentro de su srccarpeta, cree un tercer archivo. Llame a esto db.jsy, dentro de este tercer archivo, ponga el siguiente código:

export let users = [ { id: 1, name: "John Doe", email: "[email protected]", age: 22 }, { id: 2, name: "Jane Doe", email: "[email protected]", age: 23 } ];

In this tutorial we’re not using a real-world database. So this db.js file is going to simulate a database, just for learning purposes.

Now our src folder should look like this:

src |--db.js |--resolvers.js |--schema.graphql

Now, if you run the command npm run dev or, if you’re using yarn, yarn dev, you should see this output in your terminal:

You can now go to localhost:4000 . This means that we’re ready to go and start writing our first queries, mutations, and subscriptions in GraphQL.

You see the GraphQL Playground, a powerful GraphQL IDE for better development workflows. If you want to learn more about GraphQL Playground, click here.

Schema

GraphQL has its own type of language that’s used to write schemas. This is a human-readable schema syntax called Schema Definition Language (SDL). The SDL will be the same, no matter what technology you’re using — you can use this with any language or framework that you want.

This schema language its very helpful because it’s simple to understand what types your API is going to have. You can understand it just by looking right it.

Types

Types are one of the most important features of GraphQL. Types are custom objects that represent how your API is going to look. For example, if you’re building a social media application, your API should have types such as Posts, Users, Likes, Groups.

Types have fields, and these fields return a specific type of data. For example, we’re going to create a User type, we should have some name, email, and age fields. Type fields can be anything, and always return a type of data as Int, Float, String, Boolean, ID, a List of Object Types, or Custom Objects Types.

So now to write our first Type, go to your schema.graphql file and replace the type Query that is already there with the following:

type User { id: ID! name: String! email: String! age: Int }

Each User is going to have an ID, so we gave it an ID type. User is also going to have a name and email, so we gave it a String type, and an age, which we gave an Int type. Pretty simple, right?

But, what about those ! at the end of every line? The exclamation point means that the fields are non-nullable, which means that every field must return some data in each query. The only nullable field that we’re going to have in our User type will be age.

In GraphQL, you will deal with three main concepts:

  1. queries — the way you’re going to get data from the server.
  2. mutations — the way you’re going to modify data on the server and get updated data back (create, update, delete).
  3. subscriptions — the way you’re going to maintain a real-time connection with the server.

I’m going to explain all of them to you. Let’s start with Queries.

Queries

To explain this in a simple way, queries in GraphQL are how you’re going to get data. One of the most beautiful things about queries in GraphQL is that you are just going to get the exact data that you want. No more, no less. This has a huge positive impact in our API — no more over-fetching or under-fetching information as we had with REST APIs.

We’re going to create our first type Query in GraphQL. All our queries will end up inside this type. So to start, we’ll go to our schema.graphql and write a new type called Query:

type Query { users: [User!]! }

It’s very simple: the usersquery will return to us an array of one or more Users. It will not return null, because we put in the ! , which means it’s a non-nullable query. It should always return something.

But we could also return a specific user. For that we’re going to create a new query called user. Inside our Query type, put the following code:

user(id: ID!): User! 

Now our Query type should look like this:

type Query { users: [User!]! user(id: ID!): User! }

As you see, with queries in GraphQL we can also pass arguments. In this case, to query for a specific user, we’re going to pass its ID.

But, you may be wondering: how does GraphQL know where get the data? That’s why we should have a resolvers.js file. That file tells GraphQL how and where it's going to fetch the data.

First, go to our resolvers.js file and import the db.js that we just created a few moments ago. Your resolvers.js file should look like this:

import { users } from "./db"; const resolvers = { Query: { hello: () => "Hello World!" } }; export default resolvers;

Now, we’re going to create our first Query. Go to your resolvers.js file and replace the hello function. Now your Query type should look like this:

import { users } from "./db"; const resolvers = { Query: { user: (parent, { id }, context, info) => { return users.find(user => user.id === id); }, users: (parent, args, context, info) => { return users; } } }; export default resolvers;

Now, to explain how is it going to work:

Each query resolver has four arguments. In the user function, we’re going to pass id as an argument, and then return the specific user that matches the passed id. Pretty simple.

In the users function, we’re just going to return the users array that already exists. It’ll always return to us all of our users.

Now, we’re going to test if our queries are working fine. Go to localhost:4000 and put in the following code:

query { users { id name email age } }

It should return to you all of our users.

Or, if you want to return a specific user:

query { user(id: 1) { id name email age } }

Now, we’re going to start learning about mutations, one of the most important features in GraphQL.

Mutations

In GraphQL, mutations are the way you’re going to modify data on the server and get updated data back. You can think like the CUD (Create, Update, Delete) of REST.

We’re going to create our first type mutation in GraphQL, and all our mutations will end up inside this type. So, to start, go to our schema.graphql and write a new type called mutation:

type Mutation { createUser(id: ID!, name: String!, email: String!, age: Int): User! updateUser(id: ID!, name: String, email: String, age: Int): User! deleteUser(id: ID!): User! }

As you can see, we’re going to have three mutations:

createUser: we should pass an ID, name, email, and age. It should return a new user to us.

updateUser: we should pass an ID, and a new name, email, or age. It should return a new user to us.

deleteUser: we should pass an ID. It should return a new user to us.

Now, go to our resolvers.js file and below the Query object, create a new mutation object like this:

Mutation: { createUser: (parent, { id, name, email, age }, context, info) => { const newUser = { id, name, email, age }; users.push(newUser); return newUser; }, updateUser: (parent, { id, name, email, age }, context, info) => { let newUser = users.find(user => user.id === id); newUser.name = name; newUser.email = email; newUser.age = age; return newUser; }, deleteUser: (parent, { id }, context, info) => { const userIndex = users.findIndex(user => user.id === id); if (userIndex === -1) throw new Error("User not found."); const deletedUsers = users.splice(userIndex, 1); return deletedUsers[0]; } }

Now, our resolvers.js file should look like this:

import { users } from "./db"; const resolvers = { Query: { user: (parent, { id }, context, info) => { return users.find(user => user.id === id); }, users: (parent, args, context, info) => { return users; } }, Mutation: { createUser: (parent, { id, name, email, age }, context, info) => { const newUser = { id, name, email, age }; users.push(newUser); return newUser; }, updateUser: (parent, { id, name, email, age }, context, info) => { let newUser = users.find(user => user.id === id); newUser.name = name; newUser.email = email; newUser.age = age; return newUser; }, deleteUser: (parent, { id }, context, info) => { const userIndex = users.findIndex(user => user.id === id); if (userIndex === -1) throw new Error("User not found."); const deletedUsers = users.splice(userIndex, 1); return deletedUsers[0]; } } }; export default resolvers;

Now, we’re going to test if our mutations are working fine. Go to localhost:4000 and put in the following code:

mutation { createUser(id: 3, name: "Robert", email: "[email protected]", age: 21) { id name email age } }

It should return a new user to you. If you want to try making new mutations, I recommend you to try for yourself! Try to delete this same user that you created to see if it’s working fine.

Finally, we’re going to start learning about subscriptions, and why they are so powerful.

Subscriptions

As I said before, subscriptions are the way you’re going to maintain a real-time connection with a server. That means that whenever an event occurs in the server and whenever that event is called, the server will send the corresponding data to the client.

By working with subscriptions, you can keep your app updated to the latest changes between different users.

A basic subscription is like this:

subscription { users { id name email age } }

You will say it’s very similar to a query, and yes it is. But it works differently.

When something is updated in the server, the server will run the GraphQL query specified in the subscription, and send a newly updated result to the client.

We’re not going to work with subscriptions in this specific article, but if you want to read more about them click here.

Conclusion

As you have seen, GraphQL is a new technology that is really powerful. It gives us real power to build better and well-designed APIs. That’s why I recommend you start to learn it now. For me, it will eventually replace REST.

Thanks for reading the article.

Follow me on Twitter!

Follow me on GitHub!

I’m looking for a remote opportunity, so if have any I’d love to hear about it, so please contact me at my Twitter!