Docs: Improve DataLoader example from O(n²) to O(n) (#7589)

apollographql · May 30, 2023 · bcf5eea · bcf5eea
1 parent 940d1f9
commit bcf5eea
Showing 1 changed file with 7 additions and 1 deletion.
diff --git a/docs/source/data/fetching-data.mdx b/docs/source/data/fetching-data.mdx
@@ -102,7 +102,13 @@ class ProductsDataSource {
 
   private batchProducts = new DataLoader(async (ids) => {
     const productList = await this.dbConnection.fetchAllKeys(ids);
-    return ids.map((id) => productList.find((product) => product.id === id));
+    // Dataloader expects you to return a list with the results ordered just like the list in the arguments were
+    // Since the database might return the results in a different order the following code sorts the results accordingly
+    const productIdToProductMap = productList.reduce((mapping, product) => {
+        mapping[product.id] = product;
+        return mapping;
+    }, {});
+    return ids.map((id) => productIdToProductMap[id]);
   });
 
   async getProductFor(id) {