Part 3: Building a REST API with NestJS and Prisma: Error Handling

src/articles/articles.controller.ts

@@ -1,4 +1,4 @@
-import { Controller, Get, Post, Body, Patch, Param, Delete, ParseIntPipe } from '@nestjs/common';
+import { Controller, Get, Post, Body, Patch, Param, Delete, NotFoundException, ParseIntPipe } from '@nestjs/common';
 import { ArticlesService } from './articles.service';
 import { CreateArticleDto } from './dto/create-article.dto';
 import { UpdateArticleDto } from './dto/update-article.dto';
@@ -30,8 +30,12 @@ export class ArticlesController {
 
   @Get(':id')
   @ApiOkResponse({ type: ArticleEntity })
-  findOne(@Param('id', ParseIntPipe) id: number) {
-    return this.articlesService.findOne(id);
+  async findOne(@Param('id', ParseIntPipe) id: number) {
+    const article = await this.articlesService.findOne(id)
+    if (!article) {
+      throw new NotFoundException(`Article with ${id} does not exist.`)
+    }
+    return article
   }
 
   @Patch(':id')

src/main.ts

@@ -1,7 +1,8 @@
-import { NestFactory } from '@nestjs/core';
+import { HttpAdapterHost, NestFactory } from '@nestjs/core';
 import { AppModule } from './app.module';
 import { SwaggerModule, DocumentBuilder } from '@nestjs/swagger';
 import { ValidationPipe } from '@nestjs/common'
+import { PrismaClientExceptionFilter } from './prisma-client-exception/prisma-client-exception.filter';
 
 async function bootstrap() {
   const app = await NestFactory.create(AppModule);
@@ -17,6 +18,9 @@ async function bootstrap() {
   const document = SwaggerModule.createDocument(app, config)
   SwaggerModule.setup('api', app, document)
 
+  const { httpAdapter } = app.get(HttpAdapterHost)
+  app.useGlobalFilters(new PrismaClientExceptionFilter(httpAdapter))
+
   await app.listen(3000);
 }
 bootstrap();

src/prisma-client-exception/prisma-client-exception.filter.spec.ts

@@ -0,0 +1,7 @@
+import { PrismaClientExceptionFilter } from './prisma-client-exception.filter';
+
+describe('PrismaClientExceptionFilter', () => {
+  it('should be defined', () => {
+    expect(new PrismaClientExceptionFilter()).toBeDefined();
+  });
+});

src/prisma-client-exception/prisma-client-exception.filter.ts

@@ -0,0 +1,39 @@
+//src/prisma-client-exception.filter.ts
+
+import { ArgumentsHost, Catch, HttpStatus } from '@nestjs/common';
+import { BaseExceptionFilter } from '@nestjs/core';
+import { Prisma } from '@prisma/client';
+import { Response } from 'express';
+
+@Catch(Prisma.PrismaClientKnownRequestError)
+export class PrismaClientExceptionFilter extends BaseExceptionFilter {
+  catch(exception: Prisma.PrismaClientKnownRequestError, host: ArgumentsHost) {
+    console.error(exception.message);
+    const ctx = host.switchToHttp();
+    const response = ctx.getResponse<Response>();
+    const message = exception.message.replace(/\n/g, '');
+
+    switch (exception.code) {
+      case 'P2002': {
+        const status = HttpStatus.CONFLICT;
+        response.status(status).json({
+          statusCode: status,
+          message: message,
+        });
+        break;
+      }
+      case 'P2025': {
+        const status = HttpStatus.NOT_FOUND;
+        response.status(status).json({
+          statusCode: status,
+          message: message,
+        });
+        break;
+      }
+      default:
+        // default 500 error code
+        super.catch(exception, host);
+        break;
+    }
+  }
+}