metropolis/src/items/items.service.ts

import { Injectable } from '@nestjs/common';
import { InjectEntityManager, InjectRepository } from '@nestjs/typeorm';
import { EntityManager, Repository, TreeRepository } from 'typeorm';
import { NewItemInput } from './dto/new-item.input';
import { Item } from './items.entity';
import { ItemModel } from './items.model';

@Injectable()
export class ItemsService {
  constructor(
    @InjectRepository(Item)
    private itemRepository: Repository<Item>,
    @InjectEntityManager()
    private entityManager: EntityManager,
  ) {
    this.treeRepository = this.entityManager.getTreeRepository(Item);
  }
  treeRepository: TreeRepository<Item>;

  async getItem(id: string): Promise<Item | undefined> {
    return this.itemRepository.findOne(id);
  }

  async getItemParent(item: ItemModel): Promise<Item | undefined> {
    const childItem = await this.itemRepository.findOneOrFail(item.id, {
      relations: ['parent'],
    });
    return childItem.parent;
  }

  async getItemChildren(item: ItemModel): Promise<Item[]> {
    return this.itemRepository.find({
      where: {
        parent: item.id,
      },
    });
  }

  async getItemDescendents(item: ItemModel): Promise<Item[]> {
    const parentItem = await this.itemRepository.findOneOrFail(item.id, {
      relations: ['parent'],
    });
    return this.treeRepository.findDescendants(parentItem);
  }

  async createItem(input: NewItemInput): Promise<Item> {
    const item = this.itemRepository.create({
      ...input,
      id: input.id || undefined,
      parent: input.parent
        ? await this.itemRepository.findOneOrFail(input.parent)
        : undefined,
    });

    const highestIdQuery = this.itemRepository
      .createQueryBuilder()
      .select('id')
      .orderBy('id', 'DESC')
      .limit(1);

    const insert = await this.itemRepository
      .createQueryBuilder()
      .insert()
      .into(Item)
      .values({
        ...item,
        // if id is specified, use it.
        // if not, get the highest id in table and use highest_id+1
        id: input.id || (() => `((${highestIdQuery.getSql()}) + 1)`),
      })
      .returning(['id'])
      .execute();

    item.id = insert.identifiers[0].id || item.id;
    return item;
  }
}