Question

我正在使用MobX，并且该存储库包含我的应用程序中的所有实体。

我想拥有两个功能

addEntity：：获取一个实体并更新/插入
getEntity：如果未定义则返回该实体

但是我也希望它们是类型安全的。

假设我保留此收藏集：

@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)

我已经尝试了很多使用泛型的方法，但是我做不到。我必须添加类型转换为的通用类型所以我的电话是这样的：

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

有一个技巧可以使这项工作成功吗？

Answer 1

不确定MobX部分，但打字稿类型是索引类型查询和keyof的直接应用：

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：根据应用于键控对象的字符串文字联合推断正确的类型

1 个答案: