feat(api): add dataloader to avoid refetching db

packages/api/package.json

@@ -34,6 +34,7 @@
   },
   "dependencies": {
     "apollo-server": "^2.22.1",
+    "dataloader": "2.0.0",
     "dotenv": "^10.0.0",
     "graphql": "^15.5.0",
     "jest": "^27.0.1",

packages/api/src/loaders/index.ts

@@ -0,0 +1,53 @@
+import DataLoader from 'dataloader'
+import { Repositories, ResultRequestDbObjectNormalized } from '../types'
+
+export class Loaders {
+  repositories: Repositories
+
+  constructor (repositories: Repositories) {
+    this.repositories = repositories
+  }
+  // returns a loader that fetches data using the given function
+  private genericLoader<T> (load: (filter) => T) {
+    return new DataLoader(async (filters: Array<string>) => {
+      // load data from all
+      const data = await Promise.all(
+        await filters.map(async (filter, index) => ({
+          data: await load(filter),
+          index
+        }))
+      )
+      // ensure they are sorted
+      const fetchedDataByIndex = data.reduce((acc, val) => {
+        acc[val.index] = val.data
+
+        return acc
+      }, {})
+      return filters.map((_, index) => fetchedDataByIndex[index] || null)
+    })
+  }
+
+  getLoaders (): {
+    lastResult: DataLoader<string, ResultRequestDbObjectNormalized, string>
+    requests: DataLoader<string, ResultRequestDbObjectNormalized, string>
+  } {
+    return {
+      lastResult: this.genericLoader<Promise<ResultRequestDbObjectNormalized>>(
+        async (feedFullName: string) =>
+          await this.repositories.resultRequestRepository.getLastResult(
+            feedFullName
+          )
+      ),
+
+      requests: this.genericLoader<
+        Promise<Array<ResultRequestDbObjectNormalized>>
+      >(
+        async (filter: { feedFullName: string; timestamp: number }) =>
+          await this.repositories.resultRequestRepository.getFeedRequests(
+            filter.feedFullName,
+            filter.timestamp
+          )
+      )
+    }
+  }
+}

packages/api/src/repository/ResultRequest.ts

@@ -68,7 +68,7 @@ export class ResultRequestRepository {
 
   async getLastResult (
     feedFullName: string
-  ): Promise<ResultRequestDbObjectNormalized> {
+  ): Promise<ResultRequestDbObjectNormalized | null> {
     const lastResultRequest = await this.collection.findOne(
       {
         feedFullName
@@ -83,6 +83,7 @@ export class ResultRequestRepository {
         }
       }
     )
+
     return this.normalizeId(lastResultRequest)
   }
 
@@ -104,7 +105,7 @@ export class ResultRequestRepository {
 
   private normalizeId (
     resultRequest: ResultRequestDbObject
-  ): ResultRequestDbObjectNormalized {
+  ): ResultRequestDbObjectNormalized | null {
     if (resultRequest?._id) {
       return { ...resultRequest, id: resultRequest._id.toString() }
     } else {

packages/api/src/resolvers.ts

@@ -22,25 +22,17 @@ const resolvers = {
     }
   },
   Feed: {
-    requests: async (parent, args, { resultRequestRepository }: Context) => {
-      return await resultRequestRepository.getFeedRequests(
-        parent.feedFullName,
-        args.timestamp
-      )
+    requests: async (parent, args, { loaders }: Context) => {
+      return await loaders.requests.load({
+        feedFullName: parent.feedFullName,
+        timestamp: args.timestamp
+      })
     },
-    lastResult: async (parent, _args, { resultRequestRepository }: Context) => {
-      // FIXME: add dataloader library to avoid overfetching
-      return (await resultRequestRepository.getLastResult(parent.feedFullName))
-        ?.result
+    lastResult: async (parent, _args, { loaders }: Context) => {
+      return (await loaders.lastResult.load(parent.feedFullName))?.result
     },
-    lastResultTimestamp: async (
-      parent,
-      _args,
-      { resultRequestRepository }: Context
-    ) => {
-      // FIXME: add dataloader library to avoid overfetching
-      return (await resultRequestRepository.getLastResult(parent.feedFullName))
-        ?.timestamp
+    lastResultTimestamp: async (parent, _args, { loaders }: Context) => {
+      return (await loaders.lastResult.load(parent.feedFullName))?.timestamp
     },
     color: async (parent, _args, { config }: Context) => {
       return config[parent.feedFullName]?.color || ''

packages/api/src/server.ts

@@ -3,6 +3,7 @@ import typeDefs from './typeDefs'
 import { DIRECTIVES } from '@graphql-codegen/typescript-mongodb'
 import resolvers from './resolvers'
 import { ConfigByFullName, FeedInfo, Repositories } from './types'
+import { Loaders } from './loaders'
 
 export async function createServer (
   repositories: Repositories,
@@ -20,7 +21,13 @@ export async function createServer (
         {}
       )
 
-      return { ...repositories, config: configByFullName }
+      const loaders = new Loaders(repositories)
+
+      return {
+        ...repositories,
+        config: configByFullName,
+        loaders: loaders.getLoaders()
+      }
     }
   })
 }

packages/api/src/types.ts

@@ -4,6 +4,7 @@ import { Contract } from 'web3-eth-contract'
 
 import { FeedRepository } from './repository/Feed'
 import { ResultRequestRepository } from './repository/ResultRequest'
+import DataLoader from 'dataloader'
 
 export * from './generated/types'
 export { AbiItem } from 'web3-utils'
@@ -15,6 +16,20 @@ export type Context = {
   feedRepository: FeedRepository
   resultRequestRepository: ResultRequestRepository
   config: ConfigByFullName
+  loaders: {
+    lastResult: DataLoader<string, ResultRequestDbObjectNormalized, string>
+    requests: DataLoader<
+      {
+        feedFullName: string
+        timestamp: number
+      },
+      ResultRequestDbObjectNormalized,
+      {
+        feedFullName: string
+        timestamp: number
+      }
+    >
+  }
 }
 
 export type ConfigByFullName = {

packages/api/test/loaders/loaders.spec.ts

@@ -0,0 +1,95 @@
+import { Loaders } from '../../src/loaders'
+
+describe('loaders', () => {
+  describe('lastResult', () => {
+    it('lastResult loader should call getLastResult', async () => {
+      const getLastResultMock = jest.fn(() => ({ feedFullName: 'name' }))
+      const loaders = new Loaders({
+        resultRequestRepository: {
+          getLastResult: getLastResultMock
+        }
+      } as any)
+
+      await loaders.getLoaders().lastResult.load('feedName')
+
+      expect(getLastResultMock).toHaveBeenCalledWith('feedName')
+    })
+
+    it('lastResult loader should call getLastResult the same amount of times than filters provided', async () => {
+      const getLastResultMock = jest.fn(() => ({ feedFullName: 'name' }))
+      const loaders = new Loaders({
+        resultRequestRepository: {
+          getLastResult: getLastResultMock
+        }
+      } as any)
+
+      await loaders.getLoaders().lastResult.load('feedName1')
+      await loaders.getLoaders().lastResult.load('feedName2')
+
+      expect(getLastResultMock).toHaveBeenNthCalledWith(1, 'feedName1')
+      expect(getLastResultMock).toHaveBeenNthCalledWith(2, 'feedName2')
+    })
+
+    it('lastResult loader should return the result of calling getLastResult', async () => {
+      const getLastResultMock = jest.fn(() => ({ feedFullName: 'name' }))
+      const loaders = new Loaders({
+        resultRequestRepository: {
+          getLastResult: getLastResultMock
+        }
+      } as any)
+
+      const result = await loaders.getLoaders().lastResult.load('feedName')
+
+      expect(result).toStrictEqual({ feedFullName: 'name' })
+    })
+  })
+
+  describe('getRequests', () => {
+    it('should call getFeedRequests', async () => {
+      const getFeedRequestsMock = jest.fn(() => ({ feedFullName: 'name' }))
+      const loaders = new Loaders({
+        resultRequestRepository: {
+          getFeedRequests: getFeedRequestsMock
+        }
+      } as any)
+
+      await loaders
+        .getLoaders()
+        .requests.load({ feedFullName: 'feedName', timestamp: 1 } as any)
+
+      expect(getFeedRequestsMock).toHaveBeenCalledWith('feedName', 1)
+    })
+
+    it('should call getFeedRequests the same amount of times than filters provided', async () => {
+      const getFeedRequestsMock = jest.fn(() => ({ feedFullName: 'name' }))
+      const loaders = new Loaders({
+        resultRequestRepository: {
+          getFeedRequests: getFeedRequestsMock
+        }
+      } as any)
+
+      await loaders
+        .getLoaders()
+        .requests.load({ feedFullName: 'feedName1', timestamp: 1 } as any)
+      await loaders
+        .getLoaders()
+        .requests.load({ feedFullName: 'feedName2', timestamp: 2 } as any)
+
+      expect(getFeedRequestsMock).toHaveBeenNthCalledWith(1, 'feedName1', 1)
+      expect(getFeedRequestsMock).toHaveBeenNthCalledWith(2, 'feedName2', 2)
+    })
+
+    it('should return the result of calling getFeedRequests', async () => {
+      const getFeedRequestsMock = jest.fn(() => ({ feedFullName: 'name' }))
+      const loaders = new Loaders({
+        resultRequestRepository: {
+          getFeedRequests: getFeedRequestsMock
+        }
+      } as any)
+
+      const result = await loaders.getLoaders().requests.load('feedName')
+
+      expect(result).toStrictEqual({ feedFullName: 'name' })
+    })
+  })
+})