如何在GraphQL中扩展类型？

Question

例如，a Pet是Animal带有owner和的name。

type Animal {
  species: String
}

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

Answer 1

虽然您无法创建子类/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

上面链接中的示例：

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 2

从GraphQL规范的June2018稳定版本开始，对象类型可以扩展另一种对象类型：

对象类型扩展用于表示从某种原始类型扩展过来的类型。例如，这可能用于表示本地数据

在您的示例中

type Animal {
  species: String
}

extend type Animal {
  owner: Owner
  name: String
}

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

该graphql.org文件没有提及任何东西extend，但文档是无可否认的低迷和正在转变，从Facebook的所有权转让给Linux基金会。JavaScript参考实现不完全支持扩展，但是由于您已经标记了问题apollo-server，因此可以使用graphql-tools，它可以：

type Animal {
  species: String
}

extend type Animal {
  owner: Owner
  name: String
}

有关实际的类型继承，请参见graphql-s2s库。

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目的有用。

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

参见示例：

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 {}

结果是：

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，您还可以做的是创建一些辅助函数来修改字符串并插入必要的字段。

如果您有兴趣关注 Github 上的讨论，可以查看以下问题。

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