javascript - 无法在GraphQL模式中嵌套类型

我很难找出为什么我在“页面/页面”上的PageType给出“未定义PageType”的原因，我是否有另一种方式可以引用它？我觉得这可能是一个如何忽略其他类型的简单忽略

const PageType = new GraphQLObjectType({
  name: 'Page',
  fields: {
    _id: { type: new GraphQLNonNull(GraphQLID) },
    title: { type: GraphQLString },
    subtitle: { type: GraphQLString },
    description: { type: GraphQLString },
    page: {
      type: PageType
    }
    pages: {
      type: new GraphQLList(PageType),
    }
  },
});

错误(主要是为了帮助其他人搜索类似问题):

ReferenceError: PageType is not defined
    at Object.<anonymous> (H:\Coding\Projects\react-starter-kit\build\webpack:\src\data\types\PageType.js:50:1)
    at __webpack_require__ (H:\Coding\Projects\react-starter-kit\build\webpack:\webpack\bootstrap 8ce5b4572987765a465d:19:1)
    at Object.<anonymous> (H:\Coding\Projects\react-starter-kit\build\server.js:731:74)
    at __webpack_require__ (H:\Coding\Projects\react-starter-kit\build\webpack:\webpack\bootstrap 8ce5b4572987765a465d:19:1)
    at Object.<anonymous> (H:\Coding\Projects\react-starter-kit\build\webpack:\src\data\schema.js:1:1)
    at __webpack_require__ (H:\Coding\Projects\react-starter-kit\build\webpack:\webpack\bootstrap 8ce5b4572987765a465d:19:1)
    at Object.<anonymous> (H:\Coding\Projects\react-starter-kit\build\server.js:1098:72)
    at __webpack_require__ (H:\Coding\Projects\react-starter-kit\build\webpack:\webpack\bootstrap 8ce5b4572987765a465d:19:1)
    at Object.<anonymous> (H:\Coding\Projects\react-starter-kit\build\server.js:7455:18)
    at __webpack_require__ (H:\Coding\Projects\react-starter-kit\build\webpack:\webpack\bootstrap 8ce5b4572987765a465d:19:1)
    at H:\Coding\Projects\react-starter-kit\build\webpack:\webpack\bootstrap 8ce5b4572987765a465d:65:1
    at Object.<anonymous> (H:\Coding\Projects\react-starter-kit\build\server.js:71:10)
    at Module._compile (module.js:570:32)
    at Object.Module._extensions..js (module.js:579:10)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)

最佳答案

该错误非常简单..您正在尝试在进行赋值之前引用PageType。一个最小的例子将发生相同的错误:

const foo = {
  innerFoo: foo // error: foo is not defined
}

这就是为什么在这些递归情况下使用通常称为thunk的函数的原因

const foo = {
  innerFoo: () => foo
}

在调用foo.innerFoo()时，已经定义了foo，并且可以使用。出于这个原因，GraphQL模式支持将字段创建为函数。

const FooType = new GraphQLObjectType({
  name: 'Foo',
  fields: () => ({ // fields is a "thunk"
    foo: {
      type: FooType
    },
    foos: {
      type: new GraphQLList(FooType),
    }
  }),
})