feat(): composition with mixins

Author: egocentryk

src/coffees/coffees.controller.ts

@@ -13,6 +13,8 @@ import { CoffeesService } from './coffees.service'
 import { CreateCoffeeDto } from './dto/create-coffee.dto'
 import { UpdateCoffeeDto } from './dto/update-coffee.dto'
 import { CircuitBreakerInterceptor } from '../common/interceptors/circuit-breaker/circuit-breaker.interceptor'
+import { EntityExistPipe } from 'src/common/pipes/entity-exists.pipe'
+import { Coffee } from './entities/coffee.entity'
 
 @UseInterceptors(CircuitBreakerInterceptor)
 @Controller('coffees')
@@ -36,7 +38,11 @@ export class CoffeesController {
   }
 
   @Patch(':id')
-  update(@Param('id') id: string, @Body() updateCoffeeDto: UpdateCoffeeDto) {
+  update(
+    // @Param('id', EntityExistPipe(Coffee)) id: string,
+    @Param('id') id: string,
+    @Body() updateCoffeeDto: UpdateCoffeeDto,
+  ) {
     return this.coffeesService.update(+id, updateCoffeeDto)
   }
 

src/coffees/entities/coffee.entity.ts

@@ -1 +1,8 @@
-export class Coffee {}
+import { WithUuid } from '../../common/mixins/with-uuid.mixin'
+
+export class Coffee {
+  constructor(public name: string) {}
+}
+
+const CoffeeWithUuidCls = WithUuid(Coffee)
+const coffee = new CoffeeWithUuidCls('Flat White')

src/common/mixins/with-uuid.mixin.spec.ts

@@ -0,0 +1,7 @@
+import { WithUuidMixin } from './with-uuid.mixin';
+
+describe('WithUuidMixin', () => {
+  it('should be defined', () => {
+    expect(new WithUuidMixin()).toBeDefined();
+  });
+});

src/common/mixins/with-uuid.mixin.ts

@@ -0,0 +1,12 @@
+import { Type } from '@nestjs/common'
+import { randomUUID } from 'crypto'
+
+export function WithUuid<TBase extends Type>(Base: TBase) {
+  return class extends Base {
+    uuid = randomUUID()
+
+    regenerateUuid() {
+      this.uuid = randomUUID()
+    }
+  }
+}

src/common/pipes/entity-exists.pipe.spec.ts

@@ -0,0 +1,7 @@
+import { EntityExistsPipe } from './entity-exists.pipe';
+
+describe('EntityExistsPipe', () => {
+  it('should be defined', () => {
+    expect(new EntityExistsPipe()).toBeDefined();
+  });
+});

src/common/pipes/entity-exists.pipe.ts

@@ -0,0 +1,26 @@
+import {
+  ArgumentMetadata,
+  Inject,
+  Injectable,
+  PipeTransform,
+  Type,
+} from '@nestjs/common'
+
+export function EntityExistPipe(entityCls: Type): Type<PipeTransform> {
+  @Injectable()
+  class EntityExistsPipeCls implements PipeTransform {
+    constructor(
+      @Inject(entityCls)
+      private entityRepository: { exists(condition: unknown): Promise<void> },
+      // inline random type, but generally in normal application, this would likely
+      // represent a repository provided by an ORM
+    ) {}
+
+    async transform(value: any, metadata: ArgumentMetadata) {
+      await this.entityRepository.exists({ where: { id: value } }) // throws if entity does not exist
+      return value
+    }
+  }
+
+  return EntityExistsPipeCls
+}