NestJS : Inject Service into Models / Entities

Question

i am currently stuck on a problem, which i don't know how to propery solve:

In my NestJS application, I would like to make all my TypeORM Entities extend a BaseEntity class that provide some general features. For example, i would like to provide an additional getHashedID() method that hashed (and therefore hides) the internal ID from my API customers.

Hashing is done by a HashIdService, which provides an encode() and decode() method.

My setup looks like this (removed the Decorators for readability!):

export class User extends BaseEntity {
  id: int;
  email: string;
  name: string;
  // ...
}

export class BaseEntity {
  @Inject(HashIdService) private readonly hashids: HashIdService;

  getHashedId() {
    return this.hashids.encode(this.id);
  }
}

However, if i call the this.hashids.encode() method, it throws an exception with:

Cannot read property 'encode' of undefined

How can i inject a service into a entity/model class? Is this even possible?

UPDATE #1 In particular, i would like to "inject" the HashIdService into my Entities. Further, the Entities should have a getHashedId() method that returns their hashed ID.. As i don't want to do this "over and over again", i would like to "hide" this method in the BaseEntity as described above..

My current NestJS version is as follows:

Nest version:
+-- @nestjs/[email protected]
+-- @nestjs/[email protected]
+-- @nestjs/[email protected]
+-- @nestjs/[email protected]
+-- @nestjs/[email protected]

Thank you very much for your help!

Roselleroselyn

Why is it necessary that this particular service gets injected as opposed to just referencing a utility function? – Toy

@JesseCarter Maybe it needs something like access to DB which is otherwise injected? – Paxon

@JesseCarter I just updated my initial question. I would like to inject the HashIdService so my entites are able to hash their own ID.. How would you solve this issue? What do you mean with a "utility function"? – Roselleroselyn

You need to manually set the service, if you want to use it in the model. – Pedestrian

Did you considered extending BaseEntity and then using the extended version? – Kella

Answer 1

If you don't need to inject the HashIdService or mock it in a unit test you can simply do this:

BaseEntity.ts

import { HashIdService } from './HashIdService.ts';

export class BaseEntity {

    public id: number;

    public get hasedId() : string|null {
        const hashIdService = new HashIdService();
        return this.id ? hashIdService.encode(this.id) : null;
    }
}

User.ts

export class User extends BaseEntity {
    public email: string;
    public name: string;
    // ...
}

Then create your user:

const user = new User();
user.id = 1234;
user.name = 'Tony Stark';
user.email = '[email protected]';

console.log(user.hashedId);
//a1b2c3d4e5f6g7h8i9j0...

Commorancy

This becomes extremely difficult / impossible if HashIdService also has a DI chain. – Scarify