打字稿：从应用于键控 object 的字符串文字联合推断出正确的类型

Question

我正在使用 MobX 并拥有包含我应用程序中所有实体的存储库。

我想要两个功能

addEntity: 获取一个实体并 updates/inserts 它
getEntity: Returns 未定义的实体

但我也希望它们是类型安全的。

假设我保留这个 collection:

@observable entities = {
   authors: {} as Record<string, Author>,
   comments: {} as Record<string, Comment>,
   posts: {} as Record<string, Post>
}

我想像下面这样使用我的函数：

// "authors" should be checked against "authors" | "posts" | "comments"
// by specifying "authors" statically, I want typescript to automatically refine the return type to be Author, otherwise Author | Posts | Comment
addEntity("authors", new Author(...)) 

// same here
getEntity("authors", id)

我已经尝试了很多方法来使用泛型，但我做不好。我必须添加一个泛型类型，我将类型转换为所以我的电话是这样的：

getEntity<Author>("authors")
// but nothing prevents me from writing
getEntity<Author>("posts")

有什么技巧可以实现吗？

Answer 1

不确定 MobX 部分，但是打字稿类型是索引类型查询的非常直接的应用，keyof:

class Author { id!: string; a!: string }
class Comment { id!: string; c!: string }
class Post {id!: string; p!: string }
class Store {
    entities = {
        authors: {} as Record<string, Author>,
        comments: {} as Record<string, Comment>,
        posts: {} as Record<string, Post>
    }
}
let store = new Store();
function addEntity<K extends keyof Store['entities']>(type: K, value: Store['entities'][K][string]) {
    let collection = store.entities[type] as Record<string, typeof value>; // some type assertions required
    collection[value.id] = value;
}
function getEntity<K extends keyof Store['entities']>(type: K, id: string): Store['entities'][K][string] {

    let collection = store.entities[type] as Record<string, Store['entities'][K][string]>; // some type assertions required
    return collection[id];
}
addEntity("authors", new Author()) 
addEntity("authors", new Post())  // err

// same here
let a: Author = getEntity("authors", "1") 
let p : Post = getEntity("authors", "1") //err

打字稿：从应用于键控 object 的字符串文字联合推断出正确的类型

Typescript: Infer correct type from string literal union applied on keyed object

type-inference

typescript

mobx