Interfaces

Interfaces

builder.drizzleInterface works like builder.drizzleObject. It can define the primary type or a variant of a table. Here Viewer is a variant, leaving User as the public primary type.

Define the interface

export const Viewer = builder.drizzleInterface('users', {
  variant: 'Viewer',
  select: { columns: { id: true, role: true } },
  resolveType: (user) => (user.role === 'editor' ? 'EditorViewer' : 'AuthorViewer'),
  fields: (t) => ({
    user: t.variant('users'),
    email: t.exposeString('email'),
    drafts: t.relation('posts', {
      query: { where: { published: false }, orderBy: { id: 'asc' } },
    }),
  }),
});

resolveType uses the selected role discriminator and returns GraphQL type names. Returning names avoids a circular reference between the interface and its implementations.

Selecting a viewer implementation

builder.drizzleObject('users', {
  variant: 'EditorViewer',
  interfaces: [Viewer],
  select: { columns: { id: true, role: true } },
  fields: (t) => ({ canReviewSubmissions: t.boolean({ resolve: () => true }) }),
});
builder.drizzleObject('users', {
  variant: 'AuthorViewer',
  interfaces: [Viewer],
  select: { columns: { id: true, role: true } },
});

The interface's select is planned whenever a field returns the interface. An implementation's own selection is planned when a fragment narrows to it. Selections are not inherited; put data required by an implementation in its selection as well. An implementation may select additional columns or expressions for fields that do not belong on the interface.

Maya (userId: 1) resolves to EditorViewer with canReviewSubmissions: true. Leo (userId: 2) resolves to AuthorViewer, so the editor fragment contributes no field. The interface describes those result shapes; the authenticated root lookup enforces whose drafts are returned.

Extending an interface

Fields can be added to an interface later with builder.drizzleInterfaceField and builder.drizzleInterfaceFields, which take the interface ref (or the table name) like their drizzleObjectField(s) counterparts:

builder.drizzleInterfaceFields(Viewer, (t) => ({
  publishedPosts: t.relatedConnection('posts', {
    query: { where: { published: true } },
  }),
}));

An object type implementing a drizzle interface must be based on the same table. A plain object type that implements one is planned with the interface's table, so fragments on it will select the relations it inherits.