Fix duplicate ObjectId keys (#37)

* Fix duplicate ObjectId keys

* Fix can't delete ObjectId lead to memory leak

Author: boydaihungst

src/cache.js

@@ -1,7 +1,7 @@
 import DataLoader from 'dataloader'
 
 import { getCollection, isModel } from './helpers'
-
+import { ObjectId } from 'bson'
 // https://github.com/graphql/dataloader#batch-function
 const orderDocs = ids => docs => {
   const idMap = {}
@@ -29,14 +29,15 @@ export const createCachingMethods = ({ collection, model, cache }) => {
 
   const methods = {
     findOneById: async (id, { ttl } = {}) => {
-      const key = cachePrefix + id
+      const _id = id instanceof ObjectId ? id.toHexString() : id
+      const key = cachePrefix + _id
 
       const cacheDoc = await cache.get(key)
       if (cacheDoc) {
         return JSON.parse(cacheDoc)
       }
 
-      const doc = await loader.load(id)
+      const doc = await loader.load(_id)
       if (Number.isInteger(ttl)) {
         // https://github.com/apollographql/apollo-server/tree/master/packages/apollo-server-caching#apollo-server-caching
         cache.set(key, JSON.stringify(doc), { ttl })
@@ -48,8 +49,9 @@ export const createCachingMethods = ({ collection, model, cache }) => {
       return Promise.all(ids.map(id => methods.findOneById(id, { ttl })))
     },
     deleteFromCacheById: async id => {
-      loader.clear(id)
-      await cache.delete(cachePrefix + id)
+      const _id = id instanceof ObjectId ? id.toHexString() : id
+      loader.clear(_id)
+      await cache.delete(cachePrefix + _id)
     }
   }