apollo-type-patcher

Utility to generate Type Patcher functions for apollo-link-rest.

Goal

The apollo-link-rest library enables a smooth, frontend-first transition into GraphQL, by allowing you to leverage this query language in a project powered by a REST API (read some of the reasons here). However, since you don't have a schema for your type definitions (because you don't have a GraphQL server), you have to generate the type patcher functions yourself. This is a very verbose, time consuming and error-prone process, specially if you're trying to consume endpoints with a lot of nested fields whose types you want to normalize into the cache.

The goal of this apollo-type-patcher library is to generate the type patcher functions easily in a safe, maintainable way, with an object contaiting your type definition mappings.

Installation

To add this library to your project's dependencies simply run:

yarn add apollo-type-patcher

Usage

Try it out in the browser

Create your type definitions object. This object is in the form of

typeDefinitions = {
    TYPE: {
        FIELD: TYPE,
        ...
    },
    ...
}

for example:

// typeDefinitions.js
export const typeDefinitions = {
    Student: {
        classes: "Class",
        extra_activities: "Activities"
    },
    Class: {
        chair_professor: "Professor"
    }
}

When setting up your Apollo link rest configuration, add the type patcher as follows:

import { typePatcher } from "apollo-type-patcher";
import { RestLink } from "apollo-link-rest";
// your type definitions
import { typeDefinitions } from "./typeDefinitions";

const restLink = new RestLink({
  typePatcher: typePatcher(typeDefinitions),
  ...
});

How it works

The type patcher adds the typename property to nested types, since the root type is injected directly by Apollo:

// for the Query:
const GET_STUDENT = gql`
  query getStudent($id: ID!) {
    student(id: $id) @rest(type: "Student", path: "student/{args.id}") {
      id
      degree {
        id
      }
    }
  }
`;

// and for the type defintions:
typeDefinitions = {
    Student: {
        degree: Degree,
    },
}

// the output of the Apollo request (pre type patching) is:
student = {
    id: 60,
    degree: {
        id: 5,
    },
    __typename: "Student" // <- Added by Apollo directly
}

// the final of the Query (pos type patching) is:
student = {
    id: 60,
    degree: {
        id: 5,
        __typename: "Degree" // <- Added by the typePatcher
    },
    __typename: "Student"
}

Features

add types in nested objects

// typeDef
Student: {
    class: "Class"
}
// out
student: {
    class: {
        __typename: "Class"
    }
}

add types in nested arrays

// typeDef
Student: {
    topics: "Topic"
}
// out
student: {
    topics: [{
        __typename: "Topic"
    }, ...]
}

add types in deeply nested properties

// typeDef
Student: {
    "needs.medical_needs.insurance": "Insurance"
}
// out
student: {
    needs: {
        medical_needs: {
            insurance: {
                __typename: "Insurance"
            }
        }
    }
}

Contribute

After cloning the repo locally, you can run:

yarn // install dependencies
yarn build // build the bundle w/webpack
yarn test // run unit tests

Done with the support of @cgcote and Recare!