typePolicies

Overview

typePolicies is analogous to typePolicies option passed to InMemoryCache.

Usage

For scalar fields, Orbit also accepts Apollo's scalar field policies. Configure the scalar implementations on the cache through withApolloOptions; see custom scalars.

Let's modify bookState to to return displayName for each Book which is a concatenation of the book name and genre.

library/states/book.state.ts

import { gql } from '@apollo-orbit/angular';
import { state } from '@apollo-orbit/angular/state';
import { Book } from '../../graphql';

export const bookState = state(descriptor => descriptor
  .typeDefs(gql`
    extend type Book {
      displayName: String!
    }
  `)
  .typePolicies({
    Book: {
      fields: {
        displayName: (_existing, { readField }) => {
          const name = readField<Book['name']>('name');
          const genre = readField<Book['genre']>('genre');
          return typeof genre === 'string' ? `${name} (${genre})` : name;
        }
      }
    }
  })
);

Since *.state.ts files are included in our codegen configuration, defining local schema using typeDefs will get automatically picked up by codegen.

Next, we update book.graphql to include displayName field:

library/gql/book.graphql

fragment BookFragment on Book {
  id
  name
  genre
  authorId
  displayName @client
}

...

Now, displayName can be used in the component to display the book name along with genre.