How do you handle GraphQL errors and return partial results for mutations in NestJS?

Q: How do you handle GraphQL errors and return partial results for mutations in NestJS?

// Throw typed errors for expected failures import { UserInputError } from '@nestjs/apollo'; @Mutation(() => User) async createUser(@Args('input') input: CreateUserInput): Promise { const exists = await this.usersService.emailExists(input.email); if (exists) { throw new UserInputError('Email already registered', { extensions: { code: 'EMAIL_TAKEN', field: 'email' }, }); } return this.usersService.create(input); } // Result union pattern — errors are part of the schema @ObjectType() class CreateUserSuccess { @Field(() => User) user: User; } @ObjectType() class CreateUserError { @Field() message: string; @Field() code: string; } export const CreateUserResult = createUnionType({ name: 'CreateUserResult', types: () => [CreateUserSuccess, CreateUserError] as const, resolveType: v => ('user' in v ? CreateUserSuccess : CreateUserError), }); @Mutation(() => CreateUserResult) async createUser(@Args('input') input: CreateUserInput) { try { return { user: await this.usersService.create(input) }; } catch (e) { return { message: e.message, code: 'CREATE_FAILED' }; } } GraphQL always returns HTTP 200 — errors go in the errors array alongside partial data. UserInputError — for client validation errors; sends extensions.code to help clients identify the issue. ForbiddenError — for authorization failures inside resolvers. Result union pattern — makes errors part of the schema; clients get typed access to success and failure cases. The result union pattern is the modern preferred approach for complex mutations with multiple failure modes.

Difficulty: 6/10

Error handling, Partial responses, NestJS GraphQL

GraphQL always returns HTTP 200 — errors appear in the errors array alongside any data that was successfully resolved. Throw UserInputError or GraphQLError for expected failures. For typed error handling use the result union pattern, creating a union of success and error ObjectTypes so clients get typed access to failure cases.

GraphQL error handling and result union pattern

GraphQL error handling strategies:

1
GraphQL always returns HTTP 200 — errors go in the errors array alongside partial data.
2

How do you handle GraphQL errors and return partial results for mutations in NestJS?

Difficulty: 6/10

Error handling, Partial responses, NestJS GraphQL

GraphQL always returns HTTP 200 — errors appear in the errors array alongside any data that was successfully resolved. Throw UserInputError or GraphQLError for expected failures. For typed error handling use the result union pattern, creating a union of success and error ObjectTypes so clients get typed access to failure cases.

GraphQL error handling and result union pattern

GraphQL error handling strategies:

1
GraphQL always returns HTTP 200 — errors go in the errors array alongside partial data.
2

How do you handle GraphQL errors and return partial results for mutations in NestJS?

How do you handle GraphQL errors and return partial results for mutations in NestJS?

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