如何在 GraphQL 中扩展类型？

Question

例如，Pet 是带有owner 和name 的Animal。

type Animal {
  species: String
}

type Pet extends Animal {
  owner: Owner
  name: String
}

Answer 1

从June2018 stable version of the GraphQL spec开始，一个Object类型可以扩展另一个Object类型：

对象类型扩展用于表示从某个原始类型扩展而来的类型。例如，这可能用于表示本地数据

在你的例子中，

type Animal {
  species: String
}

extend type Animal {
  owner: Owner
  name: String
}

这本身不是继承；您只能扩展基本类型，不能基于它创建新类型。请注意，新类型没有名称；现有的Animal 类型已扩展。

graphql.org documentation 没有提到任何关于extend 的内容，但文档是admittedly lackluster 并且是transitioned 来自Facebook 对Linux 基金会的所有权。 JavaScript 参考实现doesn't fully support extensions，但既然你已经标记了你的问题apollo-server，你可以使用graphql-tools，其中does：

const { graphql } = require('graphql');
const { makeExecutableSchema } = require('graphql-tools');

const typeDefs = `
  type Person {
    name: String!
  }
  extend type Person {
    salary: Int
  }  
  type Query {
    person: Person
  }
`;

const resolvers = {
  Query: {
    person: () => ({ name: "John Doe", salary: 1234 })
  }
}  

const schema = makeExecutableSchema({ typeDefs, resolvers });

graphql(schema, '{ person {name salary} }').then((response) => {
  console.log(response);
});

对于实际的类型继承，请参阅graphql-s2s library。

Answer 2

虽然您不能创建子类/子类型，但您可以使用接口进行某种形式的继承：https://graphql.org/learn/schema/#interfaces

以上链接中的示例：

interface Character {
  id: ID!
  name: String!
  friends: [Character]
  appearsIn: [Episode]!
}

type Human implements Character {
  id: ID!
  name: String!
  friends: [Character]
  appearsIn: [Episode]!
  starships: [Starship]
  totalCredits: Int
}
 
type Droid implements Character {
  id: ID!
  name: String!
  friends: [Character]
  appearsIn: [Episode]!
  primaryFunction: String
}

查询时可以为不同的实现指定特定的字段

hero(episode: $ep) {
    name
    ... on Droid {
      primaryFunction
    }
    ... on Human {
      totalCredits
    }
  }

Answer 3

目前这在 GraphQL 中是不可能的，但是有一个实验包可能对此有用。

https://github.com/Sydsvenskan/node-graphql-partials

查看示例：

partial LinkFields {
  links(
    rel: String
    type: String
  ): [Link]
}

partial DocumentFields using LinkFields {
  uuid: ID!

  # The document type, such as x-im/article
  type: String
  # If specified, then a list of the products to which this document's availability is limited
  products: [String]
  # The human readable name of the document, often used publicly to identify the document
  title: String

  # The specific path on the web page where this document is publicly available
  path: String

  # A single metadata block
  metaBlock(
    # The specific metadata block type to get
    type: String
  ): MetadataBlock
}

interface Document using DocumentFields {}

type AuthorDocument implements Document using DocumentFields {}

结果：

type AuthorDocument implements Document {
  links(
    rel: String
    type: String
  ): [Link]

  uuid: ID!

  # The document type, such as x-im/article
  type: String
  # If specified, then a list of the products to which this document's availability is limited
  products: [String]
  # The human readable name of the document, often used publicly to identify the document
  title: String

  # The specific path on the web page where this document is publicly available
  path: String

  # A single metadata block
  metaBlock(
    # The specific metadata block type to get
    type: String
  ): MetadataBlock
}

由于这些只是字符串，您还可以创建一些辅助函数来修改字符串并插入必要的字段。

如果你有兴趣关注 Github 上的讨论，可以看看下面的 issue。

https://github.com/graphql/graphql-js/issues/703

Answer 4

其他答案是正确的，这不是专门化的类型扩展。

请注意，类型扩展似乎有两种语法。根据Apollo Federation specification，graphql-java支持@extend语法。

在 Apollo 文档中，语法似乎是：

extend type Animal

但根据联邦规范，也支持另一种语法：

type Animal @key(fields: "id") @extends

一些框架似乎只支持@ 语法。