dataloader for å kjøre færre spørringer mot databasen

backend/package.json

@@ -19,6 +19,7 @@
   "license": "ISC",
   "dependencies": {
     "@apollo/server": "^5.5.1",
+    "dataloader": "^2.2.3",
     "dotenv": "^18.0.5",
     "graphql": "^17.0.2",
     "pg": "^8.23.1"

backend/src/index.ts

@@ -3,6 +3,7 @@ import { startStandaloneServer } from '@apollo/server/standalone';
 import { pool } from './db.js';
 import { typeDefs } from './schema.js';
 import { resolvers } from './resolvers.js';
+import { Context, createLoaders } from './loaders.js';
 
 // apollo-server port number [default port 3001]
 const port = Number(process.env.PORT ?? 3001);
@@ -11,11 +12,12 @@ const port = Number(process.env.PORT ?? 3001);
 await pool.query('SELECT 1');
 
 // apollo server instance
-const server = new ApolloServer({ typeDefs, resolvers });
+const server = new ApolloServer<Context>({ typeDefs, resolvers });
 
 // pass apolloserver to standaloneserver
 const { url } = await startStandaloneServer(server, {
   listen: { port },
+  context: async () => ({ loaders: createLoaders() }),
 });
 
 console.log(`Server ready at: ${url}`);

backend/src/loaders.ts

@@ -0,0 +1,37 @@
+import DataLoader from 'dataloader';
+import { pool } from './db.js';
+
+type Facet = { id: number; name: string };
+
+function relationLoader(table: string, junc: string, fk: string) {
+  const sql = `
+    SELECT j.game_id::text AS "gameId", t.id, t.name
+    FROM ${junc} j
+    JOIN ${table} t ON t.id = j.${fk}
+    WHERE j.game_id = ANY($1::bigint[])
+    ORDER BY t.name
+  `;
+  return new DataLoader<string, Facet[]>(async (ids) => {
+    const res = await pool.query(sql, [[...ids]]);
+    const byGame = new Map<string, Facet[]>();
+    for (const { gameId, id, name } of res.rows) {
+      const list = byGame.get(gameId) ?? [];
+      list.push({ id, name });
+      byGame.set(gameId, list);
+    }
+    return ids.map((id) => byGame.get(id) ?? []);
+  });
+}
+
+export function createLoaders() {
+  return {
+    genres: relationLoader('genres', 'game_genres', 'genre_id'),
+    platforms: relationLoader('platforms', 'game_platforms', 'platform_id'),
+    stores: relationLoader('stores', 'game_stores', 'store_id'),
+    developers: relationLoader('developers', 'game_developers', 'developer_id'),
+    publishers: relationLoader('publishers', 'game_publishers', 'publisher_id'),
+    tags: relationLoader('tags', 'game_tags', 'tag_id'),
+  };
+}
+
+export type Context = { loaders: ReturnType<typeof createLoaders> };

backend/src/resolvers.ts

@@ -1,6 +1,7 @@
 import { GraphQLError } from 'graphql/error';
 import { decodeCursor, encodeCursor } from './cursor.js';
 import { pool } from './db.js';
+import type { Context } from './loaders.js';
 
 // type definitions
 type GamesArgs = {
@@ -149,6 +150,7 @@ function filterValues(args: GamesArgs) {
   ];
 }
 // resolver for koblings-tabellene i databasen
+/*
 function relation(table: string, junc: string, fk: string) {
   const sql = `
     SELECT t.id, t.name
@@ -162,6 +164,12 @@ function relation(table: string, junc: string, fk: string) {
     return res.rows;
   };
 }
+  */
+
+function relation(key: keyof Context['loaders']) {
+  return (game: { id: string }, _args: unknown, ctx: Context) =>
+    ctx.loaders[key].load(game.id);
+}
 
 // resolver-funksjoner
 async function game(_parent: unknown, args: { id: string }) {
@@ -250,12 +258,12 @@ export const resolvers = {
   Query: { game, games, genres, platforms },
 
   Game: {
-    genres: relation('genres', 'game_genres', 'genre_id'),
-    platforms: relation('platforms', 'game_platforms', 'platform_id'),
-    stores: relation('stores', 'game_stores', 'store_id'),
-    developers: relation('developers', 'game_developers', 'developer_id'),
-    publishers: relation('publishers', 'game_publishers', 'publisher_id'),
-    tags: relation('tags', 'game_tags', 'tag_id'),
+    genres: relation('genres'),
+    platforms: relation('platforms'),
+    stores: relation('stores'),
+    developers: relation('developers'),
+    publishers: relation('publishers'),
+    tags: relation('tags'),
   },
 
   GameConnection: { totalCount },