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geekpi
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[#]: collector: (lujun9972)
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[#]: translator: (geekpi)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (What is GraphQL?)
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[#]: via: (https://opensource.com/article/19/6/what-is-graphql)
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[#]: author: (Zach Lendon https://opensource.com/users/zachlendon)
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What is GraphQL?
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======
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GraphQL is a query language, an execution engine, and a specification,
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and it's leading developers to rethink how they build client and API
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applications.
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![Analytics: Charts and Graphs][1]
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GraphQL is one of the biggest buzzwords in software tech today. But _what is it_ _actually_? Is it a query language like [SQL][2]? An execution engine like the [JVM][3]? A specification like [XML][4]?
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If you answered all of the above, you are correct! [GraphQL][5] is a query language syntax, a programming language-agnostic execution engine, and a continuously evolving specification.
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Let's dive into how GraphQL can be all of these things and get a glimpse of why people are excited about it.
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### Query language
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GraphQL as a query language seems reasonable—"QL" seemed important enough to be in the name, after all. But what are we querying? It probably helps to look at a sample query request and the corresponding response.
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The following user query:
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```
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{
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user(id: 4) {
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name
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email
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phoneNumber
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}
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}
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```
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might return the following JSON response:
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```
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{
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"user": {
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"name": "Zach Lendon"
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“email”: “[zach@hydrate.io][6]”
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“phoneNumber”: “867-5309”
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}
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}
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```
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Imagine a client application querying for user details, taking the result, and using it to populate a profile screen. As a query language, one of GraphQL's core benefits is that a client application can request _only the data it needs_ and expect it to be returned in a consistent manner.
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_What_ is returning the GraphQL response, though? This is where the execution engine, typically in the form of a GraphQL server, comes into play.
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### Execution engine
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![GraphQL execution engine][7]
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The GraphQL execution engine is what is responsible for processing a GraphQL query and returning a JSON response. All GraphQL servers are made up of two core components that define the structure and behavior of the execution engine: a schema and resolvers, respectively.
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A GraphQL schema is a custom typed language that exposes which queries are both permitted (valid) and handled by a GraphQL server implementation. The schema for our user example query above might look like:
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```
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type User {
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name: String
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email: String
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phoneNumber: String
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}
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type Query {
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user: User
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}
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```
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This schema defines a user query that returns a user. Clients can request any of the fields on a user via the user query, and the GraphQL server will return only those fields in its response. By using the strongly typed schema, a GraphQL server can validate incoming queries to ensure they are valid based on the defined schema.
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Once a query is determined to be valid, it is processed by a GraphQL server by resolvers. A resolver function backs each field of each GraphQL type. An example resolver for our user query might look like:
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```
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Query: {
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user(obj, args, context, info) {
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return context.db.loadUserById(args.id).then(
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userData => new User(userData)
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)
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}
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}
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```
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While the above example is in JavaScript, GraphQL servers can be written in any number of languages. This is due to the fact that GraphQL is _also_ a specification!
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### Specification
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The GraphQL specification defines the capabilities and characteristics that GraphQL implementations must follow. As an open specification available under the Open Web Foundation Final Specification Agreement ([OWFa 1.0][8]), the technology community has the opportunity to both review what a GraphQL implementation must do to be spec-compliant and help craft the future of the language.
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While the specification is very specific about GraphQL's syntax, what is a valid query, and how a schema works, it provides no direction on how to store data or what implementation programming languages GraphQL servers should use. This is incredibly powerful and relatively unique in the software space—it allows GraphQL servers to be created in any number of programming languages, and clients will know exactly how they function since they are spec-compliant. And GraphQL server implementations have been created across many programming languages, not just ones folks might expect like JavaScript, Java, and C#, but languages like Go, Elixir, and Haskell. The language a server is implemented in will not be a barrier to adoption—not only are there implementations in many languages, but they are all open source. If there isn't an implementation in your language of choice, you are free to create your own.
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### Conclusion
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GraphQL is an exciting, relatively new entrant into the open source API space. It couples a query language and execution engine with an open source specification that defines how GraphQL implementations should look and function.
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GraphQL has already started to change how companies think about building both client and API applications. With GraphQL as part of a technology stack, front-end developers are freed to query for the data they want, and back-end developers can decouple client application needs from their back-end system architectures. Often companies journey into GraphQL by first building a GraphQL API "layer" that sits on top of their existing back-end services. This allows the client applications to begin to gain the performance and operational efficiencies they seek, while allowing the back-end teams an opportunity to determine what, if any, changes they might want to make "under the hood," behind their GraphQL layer. Often, those changes will be geared towards optimizations that will help ensure that applications using GraphQL can operate as performantly as possible. Because of the abstraction GraphQL provides, systems teams can make those changes while continuing to honor the GraphQL "contract" at their GraphQL API level.
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Because GraphQL is relatively new, developers are still finding new and exciting ways to leverage it to build better software solutions. How will GraphQL change how you build applications, and does it live up to the hype? There's only one way to find out—go out there and build something with GraphQL!
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/19/6/what-is-graphql
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作者：[Zach Lendon][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/zachlendon
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/analytics-graphs-charts.png?itok=sersoqbV (Analytics: Charts and Graphs)
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[2]: https://opensource.com/article/18/2/getting-started-sql
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[3]: https://www.cubrid.org/blog/understanding-jvm-internals/
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[4]: https://www.w3.org/TR/xml/
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[5]: http://graphql.org/
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[6]: mailto:zach@hydrate.io
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[7]: https://opensource.com/sites/default/files/pictures/graphql-execution-engine.png (GraphQL execution engine)
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[8]: http://www.openwebfoundation.org/legal/the-owf-1-0-agreements/owfa-1-0---patent-only
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127
translated/tech/20190605 What is GraphQL.md
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127
translated/tech/20190605 What is GraphQL.md
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[#]: collector: (lujun9972)
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[#]: translator: (geekpi)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (What is GraphQL?)
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[#]: via: (https://opensource.com/article/19/6/what-is-graphql)
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[#]: author: (Zach Lendon https://opensource.com/users/zachlendon)
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什么是 GraphQL？
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======
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GraphQL 是一种查询语言、执行引擎和规范，它让开发人员重新思考如何构建客户端和 API
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应用。
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![Analytics: Charts and Graphs][1]
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GraphQL 是当今软件技术中最大的流行语之一。但它_实际上_是什么？它是像 [SQL][2] 这样的查询语言吗？像 [JVM][3] 这样的执行引擎？像 [XML][4] 这样的规范？
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如果你的回答是上面这些，那么你是对的！[GraphQL][5] 是查询语言语法、编程语言无关的执行引擎和不断发展的规范。
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让我们深入了解 GraphQL 如何成为这些，并了解人们为什么对此感到兴奋。
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### 查询语言
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GraphQL 作为查询语言似乎是合理的—”QL“ 似乎足够重要，毕竟它出现在名称中。但是我们在查询什么？查看示例查询请求和相应的响应可能会有所帮助。
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以下的用户查询：
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```
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{
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user(id: 4) {
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name
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email
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phoneNumber
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}
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}
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```
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可能会返回下面的 JSON 结果：
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```
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{
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"user": {
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"name": "Zach Lendon"
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“email”: “[zach@hydrate.io][6]”
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“phoneNumber”: “867-5309”
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}
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}
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```
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想象一下，客户端应用查询用户详细信息，获取结果，并使用它填充配置文件。作为查询语言，GraphQL 的核心优势之一是客户端应用可以_只请求它需要_的数据，并期望以一致的方式返回这些数据。
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那么_什么_返回了 GraphQL 响应？这就是执行引擎（通常以 GraphQL 服务器的形式）发挥作用的地方。
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### 执行引擎
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![GraphQL execution engine][7]
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GraphQL 执行引擎负责处理 GraphQL 查询并返回 JSON 响应。所有 GraphQL 服务器由两个核心组件组成，分别定义了执行引擎的结构和行为：schema 和解析器。
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GraphQL schema 是一种自定义类型语言，它公开哪些查询既允许（有效），又由 GraphQL 服务器实现处理。上面用户示例查询的 schema 可能如下所示：
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```
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type User {
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name: String
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email: String
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phoneNumber: String
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}
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type Query {
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user: User
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}
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```
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此 schema 定义返回用户的用户查询。客户端可以通过用户查询请求用户上的任何字段，并且 GraphQL 服务器将仅返回请求的字段。通过使用强类型架构，GraphQL 服务器可以验证传入查询，以确保它们基于定义的 schema 有效。
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确定查询有效后，它由 GraphQL 服务器的解析器处理。解析器函数支持每个 GraphQL 类型的每个字段。用户查询的示例解析器可能如下所示：
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```
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Query: {
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user(obj, args, context, info) {
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return context.db.loadUserById(args.id).then(
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userData => new User(userData)
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)
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}
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}
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```
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虽然上面的例子是 JavaScript，但 GraphQL 服务器可以用任意语言编写。这是因为 GraphQL 也是_也是_一种规范！
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### 规范
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GraphQL 规范定义了 GraphQL 实现必须遵循的功能和特性。作为开放网络基金会最终规范协议（[OWFa 1.0][8]）所提供的开放规范，技术社区可以借此机会查看 GraphQL 实现必须符合规范的要求，并帮助制定 GraphQL 的未来。
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虽然该规范对 GraphQL 的语法，什么是有效查询以及 schema 进行了非常具体的说明，但它没有提供有关如何存储数据或 GraphQL 服务器应使用哪种编程语言实现的指导。这在软件领域是非常强大且相对独特。它允许以多种编程语言创建 GraphQL 服务器，并且由于它们符合规范，因此客户端将确切知道它们的工作方式。GraphQL 服务器已经有多种语言实现，人们不仅可以期望像 JavaScript、Java和 C# 这样的语言，还可以使用Go、Elixir 和 Haskell 等。服务器实现所使用的语言不会成为采用过程的障碍。它不仅存在多种语言实现，而且它们都是开源的。如果没有你选择的语言的实现，那么可以自己实现。
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### 总结
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GraphQL 是开源 API 领域中一个令人兴奋的，相对较新的参与者。它将查询语言和执行引擎与开源规范结合在一起，它定义了 GraphQL 实现的功能。
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GraphQL 已经开始改变公司对构建客户端和 API 应用的看法。通过将 GraphQL 作为技术栈的一部分，前端开发人员可以自由查询所需的数据，而后端开发人员可以将客户端应用需求与后端系统架构分离。通常，公司首先通过在其现有后端服务之上构建一个 GraphQL API “层”来使用 GraphQL。这使客户端应用开始获得寻求的性能和运营效率，同时使后端团队有机会在 GraphQL 层后面进行所需的“幕后”更改（如果有）。通常，这些更改将针对优化，这些优化将帮助确保使用 GraphQL 的应用可以尽可能高效地运行。由于 GraphQL 提供了抽象，因此系统团队可以进行更改的同时继续在其 GraphQL API 级别上遵守 GraphQL 的“合约”。
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由于 GraphQL 相对较新，因此开发人员仍在寻找新颖而激动人心的方法来利用它构建更好的软件解决方案。GraphQL 将如何改变你构建应用的方式，它不会辜负宣传吗？只有一种方法可以找到答案。去使用 GraphQL 构建一些东西！
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/19/6/what-is-graphql
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作者：[Zach Lendon][a]
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选题：[lujun9972][b]
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译者：[geekpi](https://github.com/geekpi)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/zachlendon
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/analytics-graphs-charts.png?itok=sersoqbV (Analytics: Charts and Graphs)
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[2]: https://opensource.com/article/18/2/getting-started-sql
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[3]: https://www.cubrid.org/blog/understanding-jvm-internals/
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[4]: https://www.w3.org/TR/xml/
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[5]: http://graphql.org/
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[6]: mailto:zach@hydrate.io
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[7]: https://opensource.com/sites/default/files/pictures/graphql-execution-engine.png (GraphQL execution engine)
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[8]: http://www.openwebfoundation.org/legal/the-owf-1-0-agreements/owfa-1-0---patent-only
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