Creating AoT compatible Service Factories

问题

I'm trying to create a service factory for a caching service. The major requirement is that a single service can be instanced with a different string each time.

The final result will have multiple cache services each defined by a unique databaseName. Each cache can have one or more stores also defined by a unique storeName. Other services will be able to use these stores:

mainCache                         = new Cache('main')
  ├── userStore                   = new Store(mainCache, 'user')
  │     ├── userService
  │     └── authenticationService
  │
  └── taskStore                   = new Store(mainCache, 'task')
        └── taskService

fooCache                          = new Cache('foo')
  └── barStore                    = new Store(otherCache, 'bar')

My current implementations look like this:

//indexeddb-cache.ts
import { Injectable } from '@angular/core';

@Injectable()
export class IndexedDBCache {
  constructor(
    protected databaseName : string
  ) {}
}

// indexeddb-store.ts
import { Injectable } from '@angular/core';
import { IndexedDBCache } from './indexeddb-cache';

@Injectable()
export class IndexedDBStore {
  constructor(
    protected database : IndexedDBCache,
    protected storeName : string
  ) {}
}

The services are factoried:

// test-api.cache.factory.ts
import { IndexedDBCache } from '../indexeddb-cache/indexeddb-cache';
import { IndexedDBStore } from '../indexeddb-cache/indexeddb-store';

// factory functions for FactoryProviders as exports instead of inline:
// https://github.com/rangle/angular-2-aot-sandbox#func-in-providers-usefactory-top
export function mainIndexedDBCacheFactory() { return new IndexedDBCache('main'); }
export function userIndexedDBStoreFactory(testIndexedDBCache: IndexedDBCache) { return new IndexedDBStore(testIndexedDBCache, 'user'); }
export function taskIndexedDBStoreFactory(testIndexedDBCache: IndexedDBCache) { return new IndexedDBStore(testIndexedDBCache, 'task'); }

And then provided:

// test-api.cache.ts
import { InjectionToken, Provider } from '@angular/core';
import { IndexedDBCache } from '../indexeddb-cache/indexeddb-cache';
import { IndexedDBStore } from '../indexeddb-cache/indexeddb-store';
import { mainIndexedDBCacheFactory,
         taskIndexedDBStoreFactory,
         userIndexedDBStoreFactory } from './test-api.cache.factory';

// Caches

export const mainIndexedDBCache = new InjectionToken<IndexedDBCache>('mainIndexedDBCache');

export let mainIndexedDBCacheProvider : Provider = {
  provide: mainIndexedDBCache,
  useFactory: mainIndexedDBCacheFactory
};

// Stores

export const userIndexedDBStore = new InjectionToken<IndexedDBStore>('userIndexedDBStore');

export let userIndexedDBStoreProvider : Provider = {
  provide: userIndexedDBStore, deps: [mainIndexedDBCache],
  useFactory: userIndexedDBStoreFactory
};

export const taskIndexedDBStore = new InjectionToken<IndexedDBStore>('taskIndexedDBStore');

export let taskIndexedDBStoreProvider : Provider = {
  provide: taskIndexedDBStore, deps: [mainIndexedDBCache],
  useFactory: taskIndexedDBStoreFactory
};

Declared in the main module:

// test-api-module.ts
import { NgModule, ModuleWithProviders } from '@angular/core';
import { mainIndexedDBCacheProvider,
         taskIndexedDBStoreProvider,
         userIndexedDBStoreProvider } from './test-api.cache';

@NgModule({
  imports: [], declarations: [], exports: []
})
export class TestAPIModule {
  static forRoot(): ModuleWithProviders {
    return {
      ngModule: TestAPIModule,
      providers: [
        mainIndexedDBCacheProvider,
        userIndexedDBStoreProvider,
        taskIndexedDBStoreProvider
      ]
    };
  }
}

And finally used in a service:

//user-service/user.service.ts
import { Inject, Injectable } from '@angular/core';
import { IndexedDBStore } from '../../indexeddb-cache/indexeddb-store';
import { userIndexedDBStore } from '../test-api.cache';

@Injectable()
export class UserService {
  constructor(
    @Inject(userIndexedDBStore) protected cache : IndexedDBStore
  ) {}
}

Everything works fine when using JIT compilers. When I'm trying to do AoT compilation I start receiving Warning: Can't resolve all parameters for x in y: (?). This will become an error in Angular v5.x for the string parameters of the cache and store service.

I've detailed my issue before in this question: Tokenizing for AoT compilation. Now it looks like using strings as parameters for an @Injectable() is completely impossible with the AoT compiler. Is there any other way of creating a factory for services initialized using a string as I've described?

I've created a workable example in this repository. Checkout the aot branch and npm install followed by npm run build.prod.rollup.aot should work just like that.

回答1:

Based on feedback from users @estus and @Toxicable the class that will only be instanced by a Factory should not be @Injectable itself. Removing this tag from the IndexedDBCache and IndexedDBStore classes will resolve the issue.

---

The Factory also has to be in the specific form

export function mainIndexedDBCacheFactory() { return new IndexedDBCache('main'); }

Other iterations of this definition will not work.

export const mainIndexedDBCacheFactory = function() { return new IndexedDBCache('main'); };
export let mainIndexedDBCacheFactory   = function() { return new IndexedDBCache('main'); };
export let mainIndexedDBCacheFactory   = () => new IndexedDBCache('main');

The export prefix is required even if the definition is in the same file as the Provider.

来源：https://stackoverflow.com/questions/44461657/creating-aot-compatible-service-factories