How do you write an exception filter that handles GraphQL errors differently from REST errors in NestJS?

Q: How do you write an exception filter that handles GraphQL errors differently from REST errors in NestJS?

import { GqlArgumentsHost } from '@nestjs/graphql'; import { GraphQLError } from 'graphql'; @Catch() export class GqlAndHttpExceptionFilter implements ExceptionFilter { catch(exception: unknown, host: ArgumentsHost): void { if (host.getType () === 'graphql') { const message = exception instanceof HttpException ? exception.message : 'Internal server error'; const code = exception instanceof HttpException ? this.toGqlCode(exception.getStatus()) : 'INTERNAL_SERVER_ERROR'; // NestJS serializes GraphQLError into the errors array automatically throw new GraphQLError(message, { extensions: { code } }); } else { const ctx = host.switchToHttp(); const res = ctx.getResponse (); const status = exception instanceof HttpException ? exception.getStatus() : 500; res.status(status).json({ statusCode: status }); } } private toGqlCode(status: number): string { const map: Record = { 400: 'BAD_USER_INPUT', 401: 'UNAUTHENTICATED', 403: 'FORBIDDEN', 404: 'NOT_FOUND', }; return map[status] ?? 'INTERNAL_SERVER_ERROR'; } } GraphQL always returns HTTP 200 — errors go in the errors array of the response body. Throw GraphQLError inside the filter for GraphQL context — NestJS serializes it correctly. Use GqlArgumentsHost.create(host) to access the GraphQL info, args, and context. Map HTTP status codes to GraphQL error codes: 401 to UNAUTHENTICATED, 403 to FORBIDDEN. host.getType() returns 'graphql' for GraphQL resolvers when @nestjs/graphql is configured.

Difficulty: 6/10

Exception Filters, GraphQL vs REST error handling, NestJS host detection

Check host.getType() to detect GraphQL context and throw a GraphQLError instead of sending an HTTP response. For REST, send the standard HTTP response. Use GqlArgumentsHost.create(host) to access the GraphQL execution context. Map HTTP status codes to GraphQL error codes like UNAUTHENTICATED and FORBIDDEN.

Exception filter handling both GraphQL and REST

GraphQL vs REST error handling differences:

1
GraphQL always returns HTTP 200 — errors go in the errors array of the response body.
2

How do you write an exception filter that handles GraphQL errors differently from REST errors in NestJS?

Difficulty: 6/10

Exception Filters, GraphQL vs REST error handling, NestJS host detection

Check host.getType() to detect GraphQL context and throw a GraphQLError instead of sending an HTTP response. For REST, send the standard HTTP response. Use GqlArgumentsHost.create(host) to access the GraphQL execution context. Map HTTP status codes to GraphQL error codes like UNAUTHENTICATED and FORBIDDEN.

Exception filter handling both GraphQL and REST

GraphQL vs REST error handling differences:

1
GraphQL always returns HTTP 200 — errors go in the errors array of the response body.
2

How do you write an exception filter that handles GraphQL errors differently from REST errors in NestJS?

How do you write an exception filter that handles GraphQL errors differently from REST errors in NestJS?

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