feat: added prisma client exception filter - specific HTTP responses

backend/src/prisma/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,
+  ): void {
+    const context = host.switchToHttp();
+    const response = context.getResponse<Response>();
+
+    switch (exception.code) {
+      case 'P2002':
+        // 409 error code when unique constraint violated
+        const statusCode = HttpStatus.CONFLICT;
+        const message = exception.message.replace(/\n/g, '');
+        response.status(statusCode).json({
+          statusCode,
+          message, // TODO: check the message if it does not expose more info than necessary
+        });
+        break;
+      // TODO: other exception codes?
+      default:
+        // default 500 error code
+        super.catch(exception, host);
+        break;
+    }
+  }
+}