How to add a helper method to TypeORM?

Question

ORM

Tell me how to correctly specify the methods

import { Column, Entity } from "typeorm";

@Entity("users")
export class User extends Template {

@Column({ name: 'firstname', nullable: true })
  firstName: string

  @Column({ name: 'lastname', nullable: true })
  lastName: string

  public get fullName(): string {
    return `${this.firstName} ${this.lastName}`
  }
}

When accessing {users.fullName}, an empty field!