Patterns

Sharing fields between types

If you have common fields or arguments that are shared across multiple types (but you don't want to use an interface to share the common logic) you can write helper functions to generate these fields for you.

Objects and Interfaces

import { ObjectRef } from '@pothos/core';
import builder from './builder';

function addCommonFields(refs: ObjectRef<unknown, { id: string }>[]) {
  for (const ref of refs) {
    builder.objectFields(ref, (t) => ({
      id: t.exposeID('id', {}),
      idLength: t.int({
        resolve: (parent) => parent.id.length,
      }),
    }));
  }
}

const WithCommonFields1 = builder.objectRef<{ id: string }>('WithCommonFields1').implement({});
const WithCommonFields2 = builder.objectRef<{ id: string }>('WithCommonFields2').implement({});

addCommonFields([WithCommonFields1, WithCommonFields2]);

This will apply the id and idLength fields to both of the object types. The ObjectRef type is what is returned when creating an object (or when calling builder.objectRef). It takes 2 generic parameters: The first is the shape a resolver is expected to resolve to for that type, and the second is the shape of the parent arg when defining a field on that type. These 2 are generally the same, but can differ for some special cases (like with loadableObject from the dataloader plugin, which allows resolvers to resolve to an ID rather than the actual object). In this case, we only care about the second parameter since we are defining fields.

If you want to define fields on an interface, you can use InterfaceRef instead. If your helper accepts both, you can differentiate the refs by using ref.kind which will be either Object or Interface.

Args

Args are a little more complicated fields on objects and interfaces. Pothos infers the shape of args for your resolvers, so you can't just add on more args later. Instead, we can define a helper that returns a set of args to apply to your field. To make this work, we need to get a few extra types:

import { ArgBuilder, InputFieldBuilder } from '@pothos/core';

export interface SchemaTypes {
  Scalars: {
    ID: {
      Input: string;
      Output: string;
    };
  };
}
export type TypesWithDefaults = PothosSchemaTypes.ExtendDefaultTypes<SchemaTypes>;

const builder = new SchemaBuilder<SchemaTypes>({});

function createCommonArgs(arg: ArgBuilder<TypesWithDefaults>) {
  return {
    id: arg.id({}),
    reason: arg({ type: 'String', required: false }),
  };
}

builder.mutationType({
  fields: (t) => ({
    mutation1: t.boolean({
      args: {
        ...createCommonArgs(t.arg),
      },
      resolve: (parent, args) => !!args.reason,
    }),
    mutation2: t.boolean({
      args: {
        ...createCommonArgs(t.arg),
      },
      resolve: (parent, args) => !!args.reason,
    }),
  }),
});

In this example SchemaTypes are the types that will be provided to the builder when it is created. Internally Pothos extends these with some default types. This extended set of types is what gets passed around in many of Pothos's internal types. To correctly type our helper function, we need to create a version of SchemaTypes with the same defaults Pothos adds in (TypesWithDefaults). Once we have TypesWithDefaults we can define a helper function that accepts an arg builder (ArgBuilder<TypesWithDefaults>) and creates a set of arguments.

The last step is to call your helper with t.arg (the arg builder), and spread the returned args into the args object for the current field.

Input fields

Input fields are similar to args, and also all need to be present when the type is defined so that Pothos can infer the correct types.

import { InputFieldBuilder } from '@pothos/core';
import builder, { TypesWithDefault } from './builder';

function createInputFields(t: InputFieldBuilder<TypesWithDefault, 'InputObject'>) {
  return {
    id: t.id({}),
    reason: t.field({ type: 'String', required: false }),
  };
}

builder.inputType('InputWithCommonFields1', {
  fields: (t) => ({
    ...createInputFields(t),
  }),
});

builder.inputType('InputWithCommonFields2', {
  fields: (t) => ({
    ...createInputFields(t),
  }),
});