[Question] How to return the `mpath` field with TreeRepository?

Issue type:

[x] question [ ] bug report [ ] feature request [ ] documentation issue

Database system/driver:

[ ] cordova [ ] mongodb [] mssql [x] mysql / mariadb [ ] oracle [ ] postgres [ ] cockroachdb [ ] sqlite [ ] sqljs [ ] react-native [ ] expo

TypeORM version:

[x] latest [ ] @next [ ] 0.x.x (or put your version here)

Steps to reproduce or a small repository showing the problem:

here is my entity

import {
  Entity,
  Column,
  PrimaryGeneratedColumn,
  CreateDateColumn,
  UpdateDateColumn,
  Tree,
  TreeChildren,
  TreeParent,
} from 'typeorm';

@Entity()
@Tree('materialized-path')
export class Permission {
  permission: Promise<Permission>;
  @PrimaryGeneratedColumn('uuid')
  id: string;

  @Column({
    length: 20,
  })
  name: string;

  @Column({
    length: 100,
  })
  identify: string;

  @Column({
    length: 20,
    nullable: true,
  })
  alias: string;

  @Column({
    type: 'int',
    default: 0,
  })
  type: number;

  @Column({
    type: 'int',
    default: 1,
  })
  isShow: number;

  @Column({
    type: 'int',
    default: false,
  })
  hasChildren: boolean;

  @Column({
    length: 100,
    nullable: true,
  })
  icon: string;

  @Column({
    type: 'int',
    default: 0,
  })
  sortId: number;

  @Column({
    length: 100,
    nullable: true,
  })
  url: string;

  @TreeChildren()
  children: Permission[];

  @TreeParent()
  parent: Permission;

  @CreateDateColumn()
  createdAt;

  @UpdateDateColumn()
  updatedAt;
}

I used the @Tree('materialized-path'), it generated the mpath parentId field in my tables

this.permissionRepository.find({
        where: { parent: pid },
      });

How can I return the mpath field ?