Typescript Mapped Template Literal Types as Index Type

Question

I'm using Typeorm and want to strongly type my raw entity results.

Let's say I know I have a class called User

class User {
   id: string;

   name: string;

   age: number;
}

When fetching raw entities in typeorm, which is sometimes useful for complex queries with performance issues, the result will be prefixed with a chosen alias in a returned piece of JSON, like so:

{ u_id: "1", u_name: "Hello", u_age: 23; }

Given that I know the keys in the User class, how can I use template literal types to create an interface corresponding to the returned JSON?

What I've tried:

type RawUser = { [K in `u_${keyof User}`]: User[K] };

Which won't work, obviously, as K is u_id, u_name etc which cannot index the User type.

Answer 1

The answer is:

type RawUser = { [K in keyof User as `u_${K}`]: User[K] };