Interested in learning JavaScript? Get my free ebook at jshandbook.com GraphQL is the new frontier in APIs ( ). Application Programming Interfaces It’s a query language for your API, and a set of server-side runtimes (implemented in various backend languages) for executing queries. It’s not tied to a specific technology, but you can implement it in any language. It is a methodology that ( ) APIs, much like REST competed with at first. directly competes with REST Representational state transfer SOAP GraphQL was , like many of the technologies that are shaking the world lately, like and React Native, and it was publicly — although Facebook used it internally for a few years before. developed at Facebook React launched in 2015 Many big companies are adopting GraphQL beside Facebook, including GitHub, Pinterest, Twitter, Sky, The New York Times, Shopify, Yelp and thousands many other. GraphQL Principles . GraphQL exposes a single endpoint You by using a special Query Language syntax. That query is . send a query to that endpoint just a string The server responds to a query by providing a JSON object. Let’s see a first example of such a query. This query gets the name of a person with : id=1 GET /graphql?query={ person(id: "1") { name } } or simply { 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 object. We don’t care about other details of the address, and the server does not return them back to us. address GET /graphql?query={ person(id: "1") { name, address { city } } } or {   person(id: "1") {     name     address {       city     }   } }

{   "name": "Tony",   "address": {     "city": "York"   } } As you can see the data we get is basically the same request we sent, filled with values. GraphQL vs REST Since REST is such a popular, or I can say universal, approach to building APIs, it’s fair to assume you are familiar with it, so let’s see the differences between GraphQL and REST. Rest is a concept REST is a de-facto architecture standard but it actually has no specification and tons of unofficial definitions. GraphQL has a draft, and it’s a instead of an architecture, with a well defined set of tools built around it (and a flourishing ecosystem). specification Query Language While REST is built on top of an existing architecture, which in the most common scenarios is HTTP, GraphQL is building its own set of conventions. Which can be an advantage point or not, since REST benefits by caching on the HTTP layer. for free A single endpoint GraphQL has only one endpoint, where you send all your queries. With a REST approach, you create multiple endpoints and use HTTP to distinguish read actions (GET) and write actions (POST, PUT, DELETE). GraphQL does not use HTTP verbs to determine the request type. verbs Tailored to your needs With REST, you generally cannot choose what the server returns back to you, unless the server implements partial responses using , and clients use that feature. The API maintainer cannot enforce such filtering. sparse fieldsets The API will usually return you much more information than what you need, unless you control the API server as well, and you tailor your responses for each different request. With you explicitly request just the information you need, you don’t “opt out” from the full response default, but it’s mandatory to pick the fields you want. GraphQL This helps saving resources on the server, since you most probably need less processing, and also network savings, since the payload to transfer is smaller. GraphQL makes it easy to monitor for fields usage With REST, unless forcing sparse fieldsets, there is no way to determine if a field is used by clients, so when it comes to refactoring or deprecating, it’s impossible to determine actual usage. GraphQL makes it possible to track which fields are used by clients. Access nested data resources GraphQL allows to generate a lot less network calls. Let’s do an example: you need to access the names of the friends of a person. If your REST API exposes a endpoint, which returns a person object with a list of friends, you generally first get the person information by doing , which contains a list of ID of its friends. /person GET /person/1 Unless the list of friends of a person already contains the friend name, with 100 friends you’d need to do 101 HTTP requests to the endpoint, which is a huge time cost, and also a resource intensive operation. /person With GraphQL, you need only one request, which asks for the names of the friends of a person. Types A REST API is based on JSON which cannot provide type control. . GraphQL has a Type System Which one is better? Organizations around the world are questioning their API technology choices and they are trying to find out if migrating from REST to GraphQL is best for their needs. GraphQL is a perfect fit when you need to expose complex data representations, and when clients might need only a subset of the data, or they regularly perform nested queries to get the data they need. As with languages, there is no single winner, it all depends on your needs. programming GraphQL Queries In this article 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, and 1 argument. The field returns an which has another field in it, a . person Object String The argument allows us to specify which person we want to reference. We pass an , but we could as well pass a argument, if the API we talk to has the option to find a person by name. id name Arguments are not limited to any particular field, we could have a field in that lists the friends of that person, and it could have a argument, to specify how many we want the API to return: friends person limit {   person(id: "1") {     name    friends(limit: 100)   } } Aliases You can ask the API to return a field with a different name, for example: {   owner: person(id: "1") {     fullname: name   } } will return {   "data": {    "owner": {       "fullname": "Tony"     }   } } This feature, beside creating more ad-hoc naming for your client code, 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 once (much useful with many 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 , a way to dynamically specify a value that is used inside a query. variables 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 query GetOwner($id: String) {   owner: person(id: $id) {     fullname: name   } } 

{   "id": "1"} In this snippet we have assigned the name to our query. Think of it as named functions, while before you had an anonymous function. Named queries are useful when you have lots of queries in your application. GetOwner The query definition with the variables looks like a function definition, and it works in an equal way. Making variables required Appending a to the type: ! query GetOwner($id: String!) instead of will make the $id variable required. $id: String Specifying a default value for a variable You can specify a default value using this syntax: query GetOwner($id: String = "1") GraphQL Directives Directives let you include or exclude a field if a variable is true or false. query GetPerson($id: String, $getAddress: Boolean) {   person(id: $id) {     fullname: name,     address: @include(if: $getAddress) {       city       street       country     }   } }

{   "id": "1",   "getAddress": false} In this case if variable we pass is true, we also get the address field, otherwise not. getAddress We have 2 directives available: , which we have just seen (includes if true), and , which is the opposite (skips if true) include skip @include(if: Boolean) query GetPerson($id: String, $getAddress: Boolean) {   person(id: $id) {     fullname: name,     address: @include(if: $getAddress) {       city       street       country     }   } } 

{  "id": "1",   "getAddress": false } @skip(if: Boolean) query GetPerson($id: String, $excludeAddress: Boolean) {   person(id: $id) {     fullname: name,     address: @skip(if: $excludeAddress) {       city       street       country     }   } }

{   "id": "1",   "excludeAddress": false } Interested in learning JavaScript? Get my free ebook at jshandbook.com

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An Introduction to GraphQL

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