Circular References

Circular references and Circular dependencies are common problem that can appear in a number of ways, and cause a variety of different issues.

Pothos has a number of built in mitigations to help avoid these issues, and tries to provide additional APIs to help with situations that can't be automatically avoided.

This guide should provide some insight into how to resolve any issues you may run into, but will hopefully mot be needed very often.

imports

Circular imports are something that can cause issues in any javascript or typescript project, but can become more common in graphql because of its interconnected nature.

When js/ts files either directly or indirectly import each other, the exports from one file will initially be undefined while executing the main body of the other. These issues often result in confusing and unrelated errors because the relevant values are often not used until much later.

Pothos mitigates this by deferring a lot of the processing until the builder.toSchema() method is called. As long as the file that builds the schema (calls the toSchema method) is not imported by any other file that defines parts of the schema, this will ensure that all types are properly imported, and types are not unexpectedly undefined.

As you can see in the example below, the references to Post and User when defining fields are wrapped inside a the fields function. Because this function is not executed until the schema is loaded, these types of Circular imports should work without causing any issues.

// user.ts
import { Post } from './post'

export const User = builder.objectType('User', {
    fields: t => ({ posts: t.t.expose('posts', { type: [Post]}) }),
})

// post.ts
import { User } from './user'

export const Post = builder.objectType('Post', {
    fields: t => ({ author: t.expose('author', {{ type: User }}) }),
})

// schema.js
export const schema = builder.toSchema()

Another best practice is to avoid importing from index.ts files by importing from the file that defines the value directly. The easiest way to achieve this is by not exporting values from index.ts files.

// bad
export * from './enums';
export * from './objects';
// better
import './enums';
import './objects';

Defining Circular or Recursive types

A large portion of the Pothos API is designed to work well with circular references, but there are a few cases where typescript is unable to resolve circular references correctly.

What should work without any issues:

Objects and interfaces referenced via a class
Objects and interfaces referenced via a string (by proving a type mapping when creating the SchemaBuilder)
Objects defined by plugins like Prisma that derive type information from an external source

Cases that may require some modification

Input objects with circular references
Object types defined with builder.objectRef
Objects defined by plugins like dataloader that infer the Backing mode type from options passed to the type.

Input objects

Defining recursive input types is described in the input Guide

Object refs

Object refs may cause issues with circular references if the refs are implemented before they are assigned to a variable. This can easily be avoided by moving the call to ref.implement into its own statement.

// May cause issues
export const User = builder.objectRef<IUser>('User').implement({...});

// Should be safe
export const User = builder.objectRef<IUser>('User')

User.implement({...});

Using object refs is often a great way to avoid issues with circular references because it allows you to define the reference before defining any fields for your type. Many of the builder methods in Pothos and its plugins can be passed a type ref instead of a name:

export const User = builder.objectRef<IUser>('User');

builder.objectType(User, {
  field: (t) => ({
    // Circular references here won't cause issues, because User is already defined above
  }),
});

Defining fields separately

Another easy work around is to define any fields that are causing issues separately

export const User = builder.objectRef<UserType>('User').implement({
  fields: (t) => ({ posts: t.expose('posts', { type: [Post] }) }),
});

export const Post = builder.objectRef<PostType>('Post').implement({
  fields: (t) => ({
    // No more circular reference
  }),
});

builder.objectField(Post, 'author', (t) => t.expose({ type: User }));

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