Enhance CanUpdateMediaUserMetadataEvent to allow it to be able to inject dependencies

Not sure if this is the best pattern, but playing it forward for now.

Author: CarsonF

src/common/create-and-inject.ts

@@ -0,0 +1,18 @@
+import { ModuleRef } from '@nestjs/core';
+import { pickBy } from 'lodash';
+import { Class } from 'type-fest';
+
+/**
+ * A helper to create an instance of a class and inject dependencies.
+ */
+export async function createAndInject<T extends Class<any>>(
+  moduleRef: ModuleRef,
+  type: T,
+  ...input: ConstructorParameters<T>
+): Promise<InstanceType<T>> {
+  const injection = await moduleRef.resolve(type);
+  const injectionProps = pickBy(injection);
+  const object = new type(...input);
+  Object.assign(object, injectionProps);
+  return object;
+}

src/common/index.ts

@@ -3,6 +3,7 @@ export { Many, many, maybeMany, JsonSet, ArrayItem } from '@seedcompany/common';
 export * from './temporal';
 export * from './calculated.decorator';
 export * from './context.type';
+export * from './create-and-inject';
 export * from './data-object';
 export * from './date-filter.input';
 export { DbLabel } from './db-label.decorator';

src/components/file/media/events/can-update-event.ts

@@ -1,14 +1,16 @@
+import { Injectable, Optional, Scope } from '@nestjs/common';
 import { PollVoter } from '~/common';
 import { AnyMedia, MediaUserMetadata } from '../media.dto';
 
 /**
  * An attempt to update the media metadata.
  * Vote with `allowUpdate` to control whether the update is allowed.
  */
+@Injectable({ scope: Scope.TRANSIENT })
 export class CanUpdateMediaUserMetadataEvent {
   constructor(
-    readonly media: AnyMedia,
-    readonly input: MediaUserMetadata,
-    readonly allowUpdate: PollVoter<boolean>,
+    @Optional() readonly media: AnyMedia,
+    @Optional() readonly input: MediaUserMetadata,
+    @Optional() readonly allowUpdate: PollVoter<boolean>,
   ) {}
 }

src/components/file/media/media.module.ts

@@ -2,6 +2,7 @@ import { forwardRef, Module } from '@nestjs/common';
 import { FileModule } from '../file.module';
 import { DetectExistingMediaMigration } from './detect-existing-media.migration';
 import { DimensionsResolver } from './dimensions.resolver';
+import { CanUpdateMediaUserMetadataEvent } from './events/can-update-event';
 import { MediaByFileVersionLoader } from './media-by-file-version.loader';
 import { MediaDetector } from './media-detector.service';
 import { MediaLoader } from './media.loader';
@@ -20,6 +21,7 @@ import { MediaService } from './media.service';
     MediaResolver,
     MediaService,
     DetectExistingMediaMigration,
+    CanUpdateMediaUserMetadataEvent,
   ],
   exports: [MediaService],
 })

src/components/file/media/media.service.ts

@@ -1,6 +1,8 @@
 import { Injectable } from '@nestjs/common';
+import { ModuleRef } from '@nestjs/core';
 import { RequireAtLeastOne } from 'type-fest';
 import {
+  createAndInject,
   IdOf,
   NotFoundException,
   Poll,
@@ -20,6 +22,7 @@ export class MediaService {
     private readonly detector: MediaDetector,
     private readonly repo: MediaRepository,
     private readonly eventBus: IEventBus,
+    private readonly moduleRef: ModuleRef,
   ) {}
 
   async detectAndSave(file: FileVersion, metadata?: MediaUserMetadata) {
@@ -40,7 +43,13 @@ export class MediaService {
   ) {
     const media = await this.repo.readOne(input);
     const poll = new Poll();
-    const event = new CanUpdateMediaUserMetadataEvent(media, input, poll);
+    const event = await createAndInject(
+      this.moduleRef,
+      CanUpdateMediaUserMetadataEvent,
+      media,
+      input,
+      poll,
+    );
     await this.eventBus.publish(event);
     if (!(poll.plurality && !poll.vetoed)) {
       throw new UnauthorizedException(