SchemaFragments.md

RFC: Schema Fragments

Problem

When writing large schemas, there is no way to reuse similar fields between ObjectTypeDefinition(s) and InputValueDefinition(s). One can use interfaces to enforce that particular fields are implemented, though this doesn't really help, as a schema creator I still have to repeat X fields on X amount of types.

Below I have Users(s) and Post(s) and where both types have the following properties; id, createdAt and updatedAt:

type User {
  id: ID # Repeated
  createdAt: DateTime # Repeated
  updatedAt: DateTime # Repeated
  name: String
}

type Post {
  id: ID # Repeated
  createdAt: DateTime # Repeated
  updatedAt: DateTime # Repeated
  content: String
}

Notice how the three properties are repeated.

As mentioned, you can use interfaces here, so for example a BaseInterface that contains the properties, and then this is implemented on each type:

interface BaseInterface {
  id: ID # Repeated
  createdAt: DateTime # Repeated
  updatedAt: DateTime # Repeated
}

type User implements BaseInterface {
  id: ID # Repeated
  createdAt: DateTime # Repeated
  updatedAt: DateTime # Repeated
  name: String
}

type Post implements BaseInterface {
  id: ID # Repeated
  createdAt: DateTime # Repeated
  updatedAt: DateTime # Repeated
  content: String
}

However, this isn't helpful at scale because your still repeating each field.

Solution

Enable the usage of fragments on ObjectTypeDefinition(s) and InputValueDefinition(s) to reduce the repetition of common fields.

Below I have Users(s) and Post(s) and where both types have the following properties; id, createdAt and updatedAt. The listed properties are only defined once and I use the fragment spread syntax to apply them to each type:

fragment BaseInterface on ObjectTypeDefinition {
  id: ID
  createdAt: DateTime
  updatedAt: DateTime
}

type User {
  ...BaseInterface
  name: String
}

type Post {
  ...BaseInterface
  content: String
}

Implementation

I assume that the GraphQL parser would need to be adapted to allow the usage of fragments on the fields, and then I see it being something that your tool should implement similar to how interfaces are enforced.