CODEWITHSUNDEEP
nestjs
Benjamin RD
Benjamin RD

Reputation: 12034

Nestjs How to extend service from Generic

I've been implemented a code, written by https://github.com/krazibit


import { Type } from '@nestjs/common'
import { InjectRepository } from '@nestjs/typeorm'
import * as DataLoader from 'dataloader'
import { keyBy } from 'lodash'
import { Repository } from 'typeorm'

export interface IDataService<T> {
    readonly repository: Repository<T>
    load: (id: string | number) => Promise<T>
    loadMany: (ids: Array<string | number>) => Promise<T[]>
}

type Constructor<I> = new (...args: any[]) => I // Main Point

export function DataService<T>(entity: Constructor<T>): Type<IDataService<T>> {
    class DataServiceHost implements IDataService<T> {
        @InjectRepository(entity) public readonly repository: Repository<T>

        private get primaryColumnName(): string {
            return this.repository.metadata.primaryColumns[0]?.propertyName
        }

        private loader: DataLoader<number | string, T> = new DataLoader(async ids => {
            const entities = await this.repository.findByIds(ids as any[])
            const entitiesKeyed = keyBy(entities, this.primaryColumnName)
            return ids.map(id => entitiesKeyed[id])
        })

        public async load(id: string | number): Promise<T> {
            return this.loader.load(id)
        }

        public async loadMany(ids: Array<string | number>): Promise<T[]> {
            return this.loadMany(ids)
        }
    }
    return DataServiceHost
}

It should be a generic function to extend to services.

But, I'm trying to implement it using:

export class MyService extends IDataService(MyEntity)

But now, I'm trying to use the methods load and loadMany but every time I try to do it, I get an error. Does someone knows how to do reference to those methods to execute them?

Upvotes: 1

Views: 2500

Answers (1)

danielevigi
danielevigi

Reputation: 389

You need to inject repository inside constructor, so:

export function DataService<T>(entity: Constructor<T>): Type<IDataService<T>> {
  class DataServiceHost implements IDataService<T> {

    constructor(@InjectRepository(entity) public readonly repository: Repository<T>) {}

    // ...
 
  }
}

Upvotes: 1

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