refactor(core): Decouple database entity registration (#15871)

Co-authored-by: Danny Martini <danny@n8n.io>

packages/@n8n/decorators/src/module/__tests__/module.test.ts

@@ -1,9 +1,9 @@
 import { Container } from '@n8n/di';
 
-import { N8nModule } from '../module';
+import { BackendModule } from '../module';
 import { ModuleMetadata } from '../module-metadata';
 
-describe('@N8nModule Decorator', () => {
+describe('@BackendModule decorator', () => {
 	let moduleMetadata: ModuleMetadata;
 
 	beforeEach(() => {
@@ -14,7 +14,7 @@ describe('@N8nModule Decorator', () => {
 	});
 
 	it('should register module in ModuleMetadata', () => {
-		@N8nModule()
+		@BackendModule()
 		class TestModule {
 			initialize() {}
 		}
@@ -26,17 +26,17 @@ describe('@N8nModule Decorator', () => {
 	});
 
 	it('should register multiple modules', () => {
-		@N8nModule()
+		@BackendModule()
 		class FirstModule {
 			initialize() {}
 		}
 
-		@N8nModule()
+		@BackendModule()
 		class SecondModule {
 			initialize() {}
 		}
 
-		@N8nModule()
+		@BackendModule()
 		class ThirdModule {
 			initialize() {}
 		}
@@ -50,7 +50,7 @@ describe('@N8nModule Decorator', () => {
 	});
 
 	it('should work with modules without initialize method', () => {
-		@N8nModule()
+		@BackendModule()
 		class TestModule {}
 
 		const registeredModules = Array.from(moduleMetadata.getModules());
@@ -62,7 +62,7 @@ describe('@N8nModule Decorator', () => {
 	it('should support async initialize method', async () => {
 		const mockInitialize = jest.fn();
 
-		@N8nModule()
+		@BackendModule()
 		class TestModule {
 			async initialize() {
 				mockInitialize();
@@ -81,10 +81,10 @@ describe('@N8nModule Decorator', () => {
 
 	describe('ModuleMetadata', () => {
 		it('should allow retrieving and checking registered modules', () => {
-			@N8nModule()
+			@BackendModule()
 			class FirstModule {}
 
-			@N8nModule()
+			@BackendModule()
 			class SecondModule {}
 
 			const registeredModules = Array.from(moduleMetadata.getModules());
@@ -95,7 +95,7 @@ describe('@N8nModule Decorator', () => {
 	});
 
 	it('should apply Service decorator', () => {
-		@N8nModule()
+		@BackendModule()
 		class TestModule {}
 
 		expect(Container.has(TestModule)).toBe(true);

packages/@n8n/decorators/src/module/index.ts

@@ -1,2 +1,2 @@
-export { BaseN8nModule, N8nModule } from './module';
+export { ModuleInterface, BackendModule, EntityClass } from './module';
 export { ModuleMetadata } from './module-metadata';

packages/@n8n/decorators/src/module/module-metadata.ts

@@ -1,12 +1,12 @@
 import { Service } from '@n8n/di';
 
-import type { Module } from './module';
+import type { ModuleClass } from './module';
 
 @Service()
 export class ModuleMetadata {
-	private readonly modules: Set<Module> = new Set();
+	private readonly modules: Set<ModuleClass> = new Set();
 
-	register(module: Module) {
+	register(module: ModuleClass) {
 		this.modules.add(module);
 	}
 

packages/@n8n/decorators/src/module/module.ts

@@ -2,14 +2,30 @@ import { Container, Service, type Constructable } from '@n8n/di';
 
 import { ModuleMetadata } from './module-metadata';
 
-export interface BaseN8nModule {
-	initialize?(): void | Promise<void>;
+/**
+ * Structurally similar (not identical) interface to typeorm's `BaseEntity`
+ * to prevent importing `@n8n/typeorm` into `@n8n/decorators`.
+ */
+export interface BaseEntity {
+	hasId(): boolean;
+	save(options?: unknown): Promise<this>;
+	remove(options?: unknown): Promise<this>;
+	softRemove(options?: unknown): Promise<this>;
+	recover(options?: unknown): Promise<this>;
+	reload(): Promise<void>;
 }
 
-export type Module = Constructable<BaseN8nModule>;
+export type EntityClass = new () => BaseEntity;
 
-export const N8nModule = (): ClassDecorator => (target) => {
-	Container.get(ModuleMetadata).register(target as unknown as Module);
+export interface ModuleInterface {
+	init?(): void | Promise<void>;
+	entities?(): EntityClass[];
+}
+
+export type ModuleClass = Constructable<ModuleInterface>;
+
+export const BackendModule = (): ClassDecorator => (target) => {
+	Container.get(ModuleMetadata).register(target as unknown as ModuleClass);
 
 	// eslint-disable-next-line @typescript-eslint/no-unsafe-return
 	return Service()(target);