是否可以有一个使用索引（类型或对象）的通用约束？

Question

I am code-generating client models(Entities) as well as corresponding Primary Keys.

I would like to have a method signature whereby predicated on the Entity, the 2nd param should be its Primary Key only.

The following use of type / class are not a requirement and may become interfaces or const for the map etc..

What I have tried is:

export type ClassType<T> = new (...args: any[]) => T

export class CustomerPk {
  customerId: number;
}

export class VendorPk {
  vendorId: number;
}

export class Customer implements CustomerPk {
  customerId: number;
  name: string;
}

export class Vendor implements VendorPk{
  vendorId: number;
  name: string;
}

export type EntityType = Customer | Vendor;
export type EntityPk = CustomerPk | VendorPk;

export type entityToPkMap = {
  Customer: CustomerPk, Vendor: VendorPk
}

To consume like so:

  constructor() {   
    const myCust = this.GetData(Customer, new CustomerPk());
    const myVend = this.GetData(Vendor, new CustomerPk());  // I want this to guard at design time.
  }
  
  // Can I(how) structure the generated code 
  //  to be able to consume similar to the following?
  public GetData<T extends EntityType, K>(entity: ClassType<T>, primaryKey: K): T {
    // Get from store.
    throw new Error('Not Implemented');
  } 

I have tried variations of the following without finding what I am looking for:

public GetData<T extends EntityType, K extends entityToPkMap[T]>(entity: ClassType<T>, primaryKey: K): T

Which errors with "Type 'T' cannot be used to index type 'entityToPkMap'."

Answer 1

You could use conditional type to resolve primary key type:

type PkMap<T> =
    T extends Customer ? CustomerPk :
    T extends Vendor ? VendorPk :
    never;

class Foo {
    constructor() {
        const myCust = this.GetData(Customer, new CustomerPk());
        const myVend = this.GetData(Vendor, new CustomerPk()); // expect error
    }

    public GetData<T>(entity: ClassType<T>, primaryKey: PkMap<T>): T {
        throw new Error('Not Implemented');
    }
}

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