作为对象的结果，其中key是数组中的每个值

Question

I am trying to figure out how it is possible to define the result of primaryKey where it is an object and each key is a value from the array $primaryKey . However I am not sure how this can be done. I don't think I can use keyof this.$primaryKey as I tried and get an error. How (if possible) can this be done?

TypeScript Playground

export type PrimaryKey = { [key: keyof Model.$primaryKey]: DBCell }

export abstract class Model extends DB {
  public $primaryKey: string[] = ['a', 'b']

  public get primaryKey(): PrimaryKey { 
    return { a: 123, b: 456 }
  }
}

Answer 1

I've managed to get PrimaryKey defined with the following changes:

public $primaryKey = ['a', 'b'] as const;

as const causes the type of $primaryKey to be inferred as ['a', 'b'] (a tuple of literal string types) instead of a plain string[] .

You can then turn this into 'a' | 'b' 'a' | 'b' using index types:

Model["$primaryKey"][number]

First set of brackets extracts the tuple type, the second set turns it into a union of its values.

From there it's trivial to create an object using the Record utility type:

export type PrimaryKey = Record<Model["$primaryKey"][number], DBCell>

TypeScript Playground