Add loader support (#44)

README.md

@@ -1,12 +1,14 @@
 # fastify-gql
 
-[![Greenkeeper badge](https://badges.greenkeeper.io/mcollina/fastify-gql.svg)](https://greenkeeper.io/)
+[![Greenkeeper badge](https://badges.greenkeeper.io/mcollina/fastify-gql.svg)](https://greenkeeper.io/) [![Build Status](https://travis-ci.com/mcollina/fastify-gql.svg?branch=master)](https://travis-ci.com/mcollina/fastify-gql)
 
 Fastify barebone GraphQL adapter.
-Queries are cached on reuse to reduce the overhead of query parsing and
-validation.
-fastify-gql supports a Just-In-Time compiler via
-[graphql-jit](http://npm.im/graphql-jit).
+
+Features:
+
+* Caching of query parsing and validation.
+* Automatic loader integration to avoid 1 + N queries.
+* Just-In-Time compiler via [graphql-jit](http://npm.im/graphql-jit).
 
 ## Install
 
@@ -96,6 +98,8 @@ __fastify-gql__ supports the following options:
   definition](https://graphql.org/graphql-js/type/#graphqlschema). The graphql schema.
   The string will be parsed.
 * `resolvers`: Object. The graphql resolvers.
+* `loaders`: Object. See [defineLoaders](#defineLoaders) for more
+  details.
 * `graphiql`: boolean. Serve
   [GraphiQL](https://www.npmjs.com/package/graphiql) on `/graphiql` if
   `routes` is `true`.
@@ -248,6 +252,70 @@ async function run () {
 run()
 ```
 
+<a name="loaders"></a>
+#### app.graphql.defineLoaders(loaders)
+
+A loader is an utility to avoid the 1 + N query problem of GraphQL.
+Each defined loader will register a resolver that coalesces each of the
+request and combines them into a single, bulk query. Morever, it can
+also cache the results, so that other parts of the GraphQL do not have
+to fetch the same data.
+
+Each loader function has the signature `loader(queries, context)`.
+`queries` is an array of objects defined as `{ obj, params }` where
+`obj` is the current object and `params` are the GraphQL params (those
+are the first two parameters of a normal resolver). The `context` is the
+GraphQL context, and it includes a `reply` object.
+
+Example:
+
+
+```js
+const loaders = {
+  Dog: {
+    async owner (queries, { reply }) {
+      return queries.map(({ obj }) => owners[obj.name])
+    }
+  }
+}
+
+app.register(GQL, {
+  schema,
+  resolvers,
+  loaders
+})
+```
+
+It is also possible disable caching with:
+
+```js
+const loaders = {
+  Dog: {
+    owner: {
+      async loader (queries, { reply }) {
+        return queries.map(({ obj }) => owners[obj.name])
+      },
+      opts: {
+        cache: false
+      }
+    }
+  }
+}
+
+app.register(GQL, {
+  schema,
+  resolvers,
+  loaders
+})
+```
+
+Disabling caching has the advantage to avoid the serialization at
+the cost of more objects to fetch in the resolvers.
+
+
+Internally, it uses
+[single-user-cache](http://npm.im/single-user-cache).
+
 #### reply.graphql(source, context, variables, operationName)
 
 Decorate [Reply](https://www.fastify.io/docs/latest/Reply/) with a

example.js → examples/basic.js

@@ -1,7 +1,7 @@
 'use strict'
 
 const Fastify = require('fastify')
-const GQL = require('.')
+const GQL = require('..')
 
 const app = Fastify()
 

examples/loaders.js

@@ -0,0 +1,68 @@
+'use strict'
+
+const Fastify = require('fastify')
+const GQL = require('..')
+
+const app = Fastify()
+
+const dogs = [{
+  name: 'Max'
+}, {
+  name: 'Charlie'
+}, {
+  name: 'Buddy'
+}, {
+  name: 'Max'
+}]
+
+const owners = {
+  'Max': {
+    name: 'Jennifer'
+  },
+  'Charlie': {
+    name: 'Sarah'
+  },
+  'Buddy': {
+    name: 'Tracy'
+  }
+}
+
+const schema = `
+  type Human {
+    name: String!
+  }
+
+  type Dog {
+    name: String!
+    owner: Human
+  }
+
+  type Query {
+    dogs: [Dog]
+  }
+`
+
+const resolvers = {
+  Query: {
+    dogs (_, params, { reply }) {
+      return dogs
+    }
+  }
+}
+
+const loaders = {
+  Dog: {
+    async owner (queries, { reply }) {
+      return queries.map(({ obj }) => owners[obj.name])
+    }
+  }
+}
+
+app.register(GQL, {
+  schema,
+  resolvers,
+  loaders,
+  graphiql: true
+})
+
+app.listen(3000)

index.js

@@ -5,6 +5,7 @@ const LRU = require('tiny-lru')
 const routes = require('./routes')
 const { BadRequest, MethodNotAllowed, InternalServerError } = require('http-errors')
 const { compileQuery } = require('graphql-jit')
+const { Factory } = require('single-user-cache')
 const {
   parse,
   buildSchema,
@@ -21,6 +22,8 @@ const {
   execute
 } = require('graphql')
 
+const kLoaders = Symbol('fastify-gql.loaders')
+
 function buildCache (opts) {
   if (opts.hasOwnProperty('cache')) {
     if (opts.cache === false) {
@@ -132,10 +135,53 @@ module.exports = fp(async function (app, opts) {
     }
   }
 
+  let factory
+
+  fastifyGraphQl.defineLoaders = function (loaders) {
+    // set up the loaders factory
+    if (!factory) {
+      factory = new Factory()
+      app.decorateReply(kLoaders)
+      app.addHook('onRequest', async function (req, reply) {
+        reply[kLoaders] = factory.create({ req, reply })
+      })
+    }
+
+    function defineLoader (name) {
+      // async needed because of throw
+      return async function (obj, params, { reply }) {
+        if (!reply) {
+          throw new Error('loaders only work via reply.graphql()')
+        }
+        return reply[kLoaders][name]({ obj, params })
+      }
+    }
+
+    const resolvers = {}
+    for (const typeKey of Object.keys(loaders)) {
+      const type = loaders[typeKey]
+      resolvers[typeKey] = {}
+      for (const prop of Object.keys(type)) {
+        const name = typeKey + '-' + prop
+        resolvers[typeKey][prop] = defineLoader(name)
+        if (typeof type[prop] === 'function') {
+          factory.add(name, type[prop])
+        } else {
+          factory.add(name, type[prop].opts, type[prop].loader)
+        }
+      }
+    }
+    fastifyGraphQl.defineResolvers(resolvers)
+  }
+
   if (opts.resolvers) {
     fastifyGraphQl.defineResolvers(opts.resolvers)
   }
 
+  if (opts.loaders) {
+    fastifyGraphQl.defineLoaders(opts.loaders)
+  }
+
   async function fastifyGraphQl (source, context, variables, operationName) {
     context = Object.assign({ app: this }, context)
     const reply = context.reply

package.json

@@ -31,6 +31,7 @@
     "graphql": "^14.1.1",
     "graphql-jit": "0.1.2",
     "http-errors": "^1.7.2",
+    "single-user-cache": "^0.3.0",
     "tiny-lru": "^6.0.0"
   }
 }