feat: Allow to provide FieldConfig via function (#3)

* feat: Allow to provide FieldConfig via function

* docs: add links to live demo and it's repo

* docs:  Adjust examples

* docs: fix demo repo link

* docs: reorganize `README.md`

Add schema building and custom fetching example.
Generalize examples.

* docs: small readme fixes

Author: nodkz

README.md

@@ -7,37 +7,34 @@
 [![Commitizen friendly](https://img.shields.io/badge/commitizen-friendly-brightgreen.svg)](http://commitizen.github.io/cz-cli/)
 [![Greenkeeper badge](https://badges.greenkeeper.io/graphql-compose/graphql-compose-rest.svg)](https://greenkeeper.io/)
 
-This is a plugin for [graphql-compose](https://github.com/nodkz/graphql-compose), which derives GraphQLType from REST response. Also derives bunch of internal GraphQL Types.
+This is a plugin for [graphql-compose](https://github.com/nodkz/graphql-compose), which generates GraphQLTypes from REST response or any JSON. It takes fields from object, determines their types and construct GraphQLObjectType with same shape.  
 
-## Getting started
+## Demo
 
-### Demo
+We have a [Live demo](https://graphql-compose-swapi.herokuapp.com/?query=%7B%0A%20%20person%28id%3A%201%29%20%7B%0A%20%20%20%20name%0A%20%20%20%20films%20%7B%0A%20%20%20%20%20%20title%0A%20%20%20%20%20%20release_date%0A%20%20%20%20%20%20director%0A%20%20%20%20%7D%0A%20%20%20%20homeworld%20%7B%0A%20%20%20%20%20%20name%0A%20%20%20%20%20%20climate%0A%20%20%20%20%20%20diameter%0A%20%20%20%20%7D%0A%20%20%20%20starships%20%7B%0A%20%20%20%20%20%20name%0A%20%20%20%20%20%20cost_in_credits%0A%20%20%20%20%7D%0A%20%20%7D%0A%7D%0A) (source code [repo](https://github.com/lyskos97/graphql-compose-swapi)) which shows how to build an API upon [SWAPI](https://swapi.co) using `graphql-compose-rest`.
 
-We have a [demo app](demo/) which shows how to build an API upon [SWAPI](https://swapi.co) using `graphql-compose-rest`.
+## Installation
 
-You can run it using:
-
-```js
-npm run demo
-```
-
-### Installation
-
-```
+```bash
 npm install graphql graphql-compose graphql-compose-rest --save
 ```
 
 Modules `graphql`, `graphql-compose`, are located in `peerDependencies`, so they should be installed explicitly in your app. They have global objects and should not have ability to be installed as submodule.
 
-### Examples
+## Example
 
-We have a sample response object:
+You have a sample response object `restApiResponse` which you can pass to `graphql-compose-rest` along with desired type name as your first argument and it will automatically generate a composed GraphQL type `PersonTC`.
 
 ```js
-const responseFromRestApi = {
+// person.js
+
+import composeWithRest from 'graphql-compose-rest';
+
+const restApiResponse = {
   name: 'Anakin Skywalker',
   birth_year: '41.9BBY',
   gender: 'male',
+  mass: 77,
   homeworld: 'https://swapi.co/api/planets/1/',
   films: [
     'https://swapi.co/api/films/5/',
@@ -51,43 +48,122 @@ const responseFromRestApi = {
     'https://swapi.co/api/starships/39/',
   ],
 };
+
+export const PersonTC = composeWithRest('Person', responseFromRestApi);
+export const PersonGraphQLType = PersonTC.getType();
 ```
 
-which we pass to a `composeWithRest` function of `graphql-compose-rest` along with desired type name as first argument in order to generate a `GraphQL` type:
+## Customization
+
+You can write custom field configs directly to a field of your API response object via function (see `mass` and `starships_count` field):
 
 ```js
-const PersonTC = composeWithRest('Person', responseFromRestApi);
+const restApiResponse = {
+  name: 'Anakin Skywalker',
+  birth_year: '41.9BBY',
+  starships: [
+    'https://swapi.co/api/starships/59/',
+    'https://swapi.co/api/starships/65/',
+    'https://swapi.co/api/starships/39/',
+  ],
+  mass: () => 'Int', // by default numbers coerced to Float, here we set up Int
+  starships_count: () => ({ // more granular field config with resolve function
+    type: 'Int',
+    resolve: source => source.starships.length,
+  }),
+};
 ```
 
-and successfully export for furher usage:
+## Schema building
+
+Now when you have your type built, you may specify the schema and data fetching method:
 
 ```js
-export PersonTC;
+// schema.js
+import { GraphQLSchema, GraphQLObjectType, GraphQLNonNull, GraphQLInt } from 'graphql';
+import fetch from 'node-fetch';
+import { PersonTC } from './person';
+
+const schema = new GraphQLSchema({
+  query: new GraphQLObjectType({
+    name: 'Query',
+    fields: {
+      person: {
+        type: PersonTC.getType(), // get GraphQL type from PersonTC
+        args: {
+          id: new GraphQLNonNull(GraphQLInt),
+        },
+        resolve: (_, args) =>
+          fetch(`https://swapi.co/api/people/${args.id}/`).then(r => r.json()),
+      },
+    },
+  }),
+});
 ```
+Or do the same via `graphql-compose`:
+```js
+import { GQC } from 'graphql-compose';
+
+GQC.rootQuery().addFields({
+  person: {
+    type: PersonTC,
+    args: {
+      id: `Int!`, // equals to `new GraphQLNonNull(GraphQLInt)`
+    },
+    resolve: (_, args) =>
+      fetch(`https://swapi.co/api/people/${args.id}/`).then(r => r.json()),
+  },
+}
+
+const schema = GQC.buildSchema(); // returns GraphQLSchema
+```
+
+## Further customization with `graphql-compose`
+
+Moreover, `graphql-compose` allows you to pass pre-defined resolvers of other types to the response object and customize them:
+
+```js
+const restApiResponse = {
+  name: 'Anakin Skywalker',
+  starships: () =>
+    PeopleTC.getResolver('findByUrlList') // get some standard resolver
+      .wrapResolve(next => rp => { // wrap with additional logic
+        const starshipsUrls = rp.source.starships;
+        rp.args.urls = starshipsUrls; // populate `urls` arg from source
+        return next(rp); // call standard resolver
+      })
+      .removeArg('urls'), // remove `urls` args from resolver and schema
+  };
+}
+
+const PersonTC = composeWithRest('Person', responseFromRestApi);
+```
+
+In case you need to separate custom field definition from your response object there are `graphql-compose` methods made for this purpose.
 
-If you want to specify new fields for your type, just use the `addField` function of `TypeComposer` type of `graphql-compose`:
+If you want to specify new fields of your type, simply use the `addFields` method of `graphql-compose`:
 
 ```js
 PersonTC.addFields({
-  weapon: { // standard GraphQL like field definition
-    type: GraphQLString,
-    resolve: (source) => source.name.toUpperCase(),
+  vehicles_count: {
+    type: 'Int!', // equals to `new GraphQLNonNull(GraphQLInt)`
+    resolve: (source) => source.vehicles.length,
   },
 });
 ```
 
-In case you want to create a relation with another type simply use `addRelation` function of `TypeComposer`:
+When you want to create a relation with another type simply use `addRelation` method of `graphql-compose`:
 
 ```js
-PersonTC.addRelation('filmObjects', { // uses shortened syntax
+PersonTC.addRelation('filmObjects', {
   resolver: () => FilmTC.getResolver('findByUrlList'),
-  prepareArgs: { // you're free to define `resolve` the way you want
+  prepareArgs: {
     urls: source => source.films,
   },
 });
 ```
 
-`graphql-compose` provides a vast variety of methods for types' `fields` and `resolvers` (aka `field configs` in vanilla `GraphQL`) management. To learn more visit [graphql-compose repo](https://github.com/nodkz/graphql-compose).
+`graphql-compose` provides a vast variety of methods for `fields` and `resolvers` (aka field configs in vanilla `GraphQL`) management of `GraphQL` types. To learn more visit [graphql-compose repo](https://github.com/nodkz/graphql-compose).
 
 ## License