我最近一直在实验React,GraphQL,Apollo和Relay符合性查询。现在,我有一个GraphQL后端,该后端具有一个带有一些Connection查询的简单graphql模式用于返回可以使用中继服务器规范进行分页的实体列表。
在前端,我发现自己在做出上述查询后重复自己的代码通常如下所示:
type isDefined = <T>(value: T | null | undefined): value is T => value !== null && value !== undefined;
export const AppleListComponent: React.FC = () => {
const { data } = useAppleQuery(); // FWIW, generating this with graphql-code-generator
const apples = data && data.apples;
const appleNodes = apples && apples.edges.map(apple => (
apple ? apple.node : undefined
)).filter(apple => isDefined(apple));
return (
<div>
{appleNodes && appleNodes.map(apple => (
<p key={apple.text}>{apple.text}</p>
))}
</div>
);
};
由于需要中继规范,所以必须检查存在的歌舞。边缘,并且节点可以为Nullable。我发现自己经常重复这种转变中继格式到简单的节点数组格式。我决定看看是否可以一个辅助函数,它需要符合连接接口的内容,并返回undefined或映射节点列表。该尝试看起来像这样:
type Maybe<T> = T | null;
type isDefined = <T>(value: T | null | undefined): value is T => value !== null && value !== undefined;
type Connection<T> = Maybe<{ edges: Array<Maybe<{ node: Maybe<T> }>>}>;
export const connectionToNodes = <T>(connection: Connection<T>): Maybe<T[]> => (
connection && connection.edges.map(edge => (
edge ? edge.node : undefined
)).filter(isDefined)
);
哪个允许以前的组件成为
export const AppleListComponent: React.FC = () => {
const { data } = useAppleQuery();
const apples = data && data.apples;
const appleNodes = connectionToNodes(apples);
return (
<div>
{appleNodes && appleNodes.map(apple => (
<p key={apple.text}>{apple.text}</p>
))}
</div>
);
};
我的问题是我的Connection类型当然不完全匹配根据我传递的类型,它具有更多类似于以下内容的属性:
Maybe<(
{ __typename?: 'AppleConnection' }
& { edges: Array<Maybe<(
{ __typename?: 'AppleEdge' }
& { node: Maybe<{ __typename?: 'AppleType' }
& { __typename?: 'QuestionType' }
& Pick<QuestionType, 'text'>
> }
)>> }
)>
因此,我最终收到有关任何类型问题的错误,以及我传递给connectionToNodes
的内容与指定的类型不匹配。我的本能是我需要说我的类型T
是其他某些事物的子类型-当然,出于应用目的,我不在乎它是Apple
还是Pear
连接/边缘/节点,但我希望最终可以推断出它-任何建议如何实现这一目标?
尝试使用此帮助程序从连接中提取节点
export type ExtractNode<T extends { edges: any }> = NonNullable<NonNullable<T['edges'][number]>['node']>;
用法
type Post = ExtractNode<FeedList_query['posts']>