Una introducción a GraphQL

GraphQL es un lenguaje de consulta para su API y un conjunto de tiempos de ejecución del lado del servidor (implementados en varios lenguajes de backend) para ejecutar consultas

Que es GraphQL

GraphQL es la nueva frontera en API (Interfaces de programación de aplicaciones) diseño, y en cómo los construimos y consumimos.

Es un lenguaje de consulta y un conjunto de tiempos de ejecución del lado del servidor (implementados en varios lenguajes de backend) para ejecutar consultas. No está vinculado a una tecnología específica, pero puede implementarlo en cualquier idioma.

Es una metodología quecompite directamente con REST(Transferencia de estado representacional) API, al igual que REST compitió conJABÓNen primer lugar.

Y como veremos, es muy diferente a REST. Crea una dimensión completamente nueva para el diseño de API.

GraphQL eradesarrollado en Facebook, como muchas de las tecnologías que están sacudiendo el mundo de JavaScript últimamente, comoReaccionary React Native, y fue públicamentelaunched in 2015- aunque Facebook lo usó internamente durante unos años antes.

Muchas grandes empresas están adoptando GraphQL además de Facebook, incluidas GitHub, Pinterest, Twitter, Sky, The New York Times, Shopify, Yelp y miles de otras.

Estuve en contacto con GraphQL por primera vez cuando GitHub decidió implementar la v4 de su API usando esa tecnología, y me uní a su programa beta. Fue entonces cuando descubrí que cambia las reglas del juego en muchos aspectos.

Cómo funciona

GraphQL expone un único punto finaldesde su servidor.

enviar una consulta a ese punto finalmediante el uso de una sintaxis de lenguaje de consulta especial. Esa consulta essolo una cuerda.

El servidor responde a una consulta proporcionando un objeto JSON.

Veamos un primer ejemplo de una consulta de este tipo. Esta consulta obtiene el nombre de una persona conid=1:

GET /graphql?query={ person(id: "1") { name } }

or:

{
  person(id: "1") {
    name
  }
}

We’ll get this JSON response back:

{
  "name": "Tony"
}

Let’s add a bit more complexity: we get the name of the person, and the city where the person lives, by extracting it from the address object. We don’t care about other details of the address, and the server does not return them back to us because we didn’t ask for them:

GET /graphql?query={ person(id: "1") { name, address { city } } }

or

{
  person(id: "1") {
    name
    address {
      city
    }
  }
}

This is what we get back:

{
  "name": "Tony",
  "address": {
    "city": "York"
  }
}

As you can see the data we get is basically the same structure of the request we sent, filled with values that were fetched.

GraphQL Queries

In this section you’ll learn how is a GraphQL query composed.

The concepts I’ll introduce are

  • fields and arguments
  • aliases
  • fragments

Fields and arguments

Take this simple GraphQL query:

{
  person(id: "1") {
    name
  }
}

In this query you see 2 fields, person and name, and 1 argument.

The field person returns an Object which has another field in it, a String.

The argument allows us to specify which person we want to reference. We pass an id, but we could as well pass a name argument, if the API we talk to has the option to find a person by name.

Arguments are not limited to any particular field. We could have a friends field in person that lists the friends of that person, and it could have a limit argument, to specify how many we want the API to return:

{
  person(id: "1") {
    name
    friends(limit: 100)
  }
}

Aliases

You can ask the API to return a field with a different name. For example here you request the name field, but you want it returned as fullname:

{
  owner: person(id: "1") {
    fullname: name
  }
}

will return

{
  "data": {
    "owner": {
      "fullname": "Tony"
    }
  }
}

This feature, beside creating more ad-hoc naming for your client code, in case you need, is the only thing that can make the query work if you need to reference the same endpoint 2 times in the same query:

{
  owner: person(id: "1") {
    fullname: name
  }
  first_employee: person(id: "2") {
    fullname: name
  }
}

Fragments

In the above query we replicated the person structure. Fragments allow us to specify the structure just once (a very useful thing when you have many similar fields):

{
  owner: person(id: "1") {
    ...personFields
  }
  first_employee: person(id: "2") {
    ...personFields
  }
}

fragment personFields on person { fullname: name }

GraphQL Variables

More complex GraphQL queries need to use variables, a way to dynamically specify a value that is used inside a query.

In this case we added the person id as a string inside the query:

{
  owner: person(id: "1") {
    fullname: name
  }
}

The id will most probably change dynamically in our program, so we need a way to pass it, and not with string interpolation.

With variables, the same query can be written as this:

query GetOwner($id: String) {
  owner: person(id: $id) {
    fullname: name
  }
}

{ “id”: “1” }

In this snippet we have assigned the GetOwner name to our query. Think of it as named functions, while previously you had an anonymous function. Named queries are useful when you have lots of queries in your application.

The query definition with the variables looks like a function definition, and it works in an equivalent way.

Making variables required

Appending a ! to the type:

query GetOwner($id: String!)

instead of $id: String will make the $id variable required.

Specifying a default value for a variable

You can specify a default value using this syntax:

query GetOwner($id: String = "1")

GraphQL Directives

Directives let you include or exclude a field if a variable is true or false.

query GetPerson($id: String) {
  person(id: $id) {
    fullname: name,
    address: @include(if: $getAddress) {
      city
      street
      country
    }
  }
}

{ “id”: “1”, “getAddress”: false }

In this case if getAddress variable we pass is true, we also get the address field, otherwise not.

We have 2 directives available: include, which we have just seen (includes if true), and skip, which is the opposite (skips if true)

@include(if: Boolean)

query GetPerson($id: String) {
  person(id: $id) {
    fullname: name,
    address: @include(if: $getAddress) {
      city
      street
      country
    }
  }
}

{ “id”: “1”, “getAddress”: false }

@skip(if: Boolean)

query GetPerson($id: String) {
  person(id: $id) {
    fullname: name,
    address: @skip(if: $excludeAddress) {
      city
      street
      country
    }
  }
}

{ “id”: “1”, “excludeAddress”: false }


More graphql tutorials: