nexus-result-field

• Installation
• Features
• Introduction
• Guide
  • Input as Object
  • Input as Plain Args
  • Result as Aggregate Error
  • Result as Single Error
• Reference Docs

Installation

npm add nexus-result-field

Peer dependencies: nexus, graphql

Features

• Implementation of GraphQL result fields schema patterns
• Type safety powered by Nexus
• API mimicks Nexus' core mutationField/queryField API making this easy to pickup.
• Accept plain args or input objects.
• Return single or multi errors.

Introduction

nexus-result-field makes it easy to encode query and mutation operation errors in your schema with Nexus.

Here are some pre-requisite readings that will probably help you understand this library:

1. Marc Andre's GraphQL Errors guide, a thorough but succinct introduction into the problem space.
2. Nexus tutorial, a primer on what Nexus is all about if you don't already know.

But if you just want a quick elevator pitch here it is:

If you are at all familiar with functional programming then you might have heard of Either and Optional/Maybe types. The idea here is similar: when a caller (the GraphQL API client) executes an operation (sends queries or mutations), instead of either returning or throwing an error (the GraphQL API equivilant of throwing is returning ad-hoc untyped errors in the JSON envelope) you encode the error case into the type system, treating it as data.

This approach to errors benefits your API clients by letting them leverage the rich GraphQL type system for not just the happy path but also the unhappy path. This makes a lot of sense for many real-world applications these two things are true:

1. You chose GraphQL in part because of its type system.
2. Your API has many IO interactions with the outside world (databases, other APIs, ...).
3. You do/want to handle errors seriously and gracefully.

The guide below will tour the main API features. For detailed reference, refer to the JSDoc.

Guide

The following guide works with resultMutationField but not there is resultQueryField which works the same way but for Query type instead of Mutation type.

Input as Object

import { makeSchema, objectType } from 'nexus'
import { printSchema } from 'graphql'
import { resultMutationField } from 'nexus-result-field'

printSchema(
  makeSchema({
    types: [
      resultMutationField({
        name: 'createFoo',
        input(t) {
          t.nonNull.string('handle')
        },
        errorTypes: ['HandleAlreadyTaken'],
        successType: `Foo`,
        resolve(_, args) {
          // ...
          return {
            __typename: `Foo`,
            id: 'abc',
            handle: args.input.handle,
          }
        },
      }),
      objectType({
        name: 'Foo',
        definition(t) {
          t.nonNull.id('id')
          t.nonNull.string('handle')
        },
      }),
      objectType({
        name: 'HandleAlreadyTaken',
        definition(t) {
          t.string('message')
        },
      }),
    ],
    features: {
      abstractTypeStrategies: {
        __typename: true,
      },
    },
  })
)

type Foo {
  id: ID!
  handle: String!
}

type HandleAlreadyTaken {
  message: String
}

union CreateFooResult = Foo | HandleAlreadyTaken

input CreateFooInput {
  handle: String!
}

type Query {
  ok: Boolean!
}

type Mutation {
  createFoo(input: CreateFooInput!): CreateFooResult
}

Input as Plain Args

import { makeSchema, objectType } from 'nexus'
import { printSchema } from 'grpahql'
import { resultMutationField } from 'nexus-result-field'

printSchema(
  makeSchema({
    types: [
      resultMutationField({
        name: 'createFoo',
        args: {
          handle: nonNull('String'),
        },
        errorTypes: ['HandleAlreadyTaken'],
        successType: `Foo`,
        resolve(_, args) {
          // ...
        },
      }),
      objectType({
        name: 'Foo',
        definition(t) {
          t.nonNull.id('id')
          t.nonNull.string('handle')
        },
      }),
      objectType({
        name: 'HandleAlreadyTaken',
        definition(t) {
          t.nonNull.string('message')
        },
      }),
    ],
    features: {
      abstractTypeStrategies: {
        __typename: true,
      },
    },
  })
)

union CreateFooResult = Foo | HandleAlreadyTaken

type Foo {
  id: ID!
  handle: String!
}

type HandleAlreadyTaken {
  message: String!
}

type Query {
  ok: Boolean!
}

type Mutation {
  createFoo(handle: String!): CreateFooResult
}

Result as Aggregate Error

import { makeSchema, objectType } from 'nexus'
import { printSchema } from 'grpahql'
import { resultMutationField } from 'nexus-result-field'

printSchema(
  makeSchema({
    types: [
      resultMutationField({
        name: 'createFoo',
        input(t) {
          t.nonNull.string('handle')
        },
        aggregateErrors: true, // <-- this
        errorTypes: ['HandleAlreadyTaken'],
        successType: `Foo`,
        resolve(_, args) {
          // ...
        },
      }),

      objectType({
        name: 'Foo',
        definition(t) {
          t.nonNull.id('id')
          t.nonNull.string('handle')
        },
      }),

      objectType({
        name: 'HandleAlreadyTaken',
        definition(t) {
          t.nonNull.string('message')
        },
      }),
    ],

    features: {
      abstractTypeStrategies: {
        __typename: true,
      },
    },
  })
)

union CreateFooResult = Foo | CreateFooErrors

type CreateFooErrors {
  errors: [CreateFooError!]!
}

union CreateFooError = HandleAlreadyTaken

input CreateFooInput {
  handle: String!
}

type Foo {
  id: ID!
  handle: String!
}

type HandleAlreadyTaken {
  message: String!
}

type Query {
  ok: Boolean!
}

type Mutation {
  createFoo(input: CreateFooInput!): CreateFooResult
}

Result as Single Error

import { makeSchema, objectType } from 'nexus'
import { printSchema } from 'grpahql'
import { resultMutationField } from 'nexus-result-field'

printSchema(
  makeSchema({
    types: [
      resultMutationField({
        name: 'createFoo',
        input(t) {
          t.nonNull.string('handle')
        },
        errorTypes: ['HandleAlreadyTaken'],
        successType: `Foo`,
        resolve(_, args) {
          // ...
          return {
            __typename: `Foo`,
            id: 'abc',
            handle: args.input.handle,
          }
        },
      }),
      objectType({
        name: 'Foo',
        definition(t) {
          t.nonNull.id('id')
          t.nonNull.string('handle')
        },
      }),
      objectType({
        name: 'HandleAlreadyTaken',
        definition(t) {
          t.string('message')
        },
      }),
    ],
    features: {
      abstractTypeStrategies: {
        __typename: true,
      },
    },
  })
)

type Foo {
  id: ID!
  handle: String!
}

type HandleAlreadyTaken {
  message: String
}

union CreateFooResult = Foo | HandleAlreadyTaken

input CreateFooInput {
  handle: String!
}

type Query {
  ok: Boolean!
}

type Mutation {
  createFoo(input: CreateFooInput!): CreateFooResult
}

Reference Docs

Read reference documentation on Paka