Detect Scaling Issues When Loading Data In a GraphQL API

Cache Database Requests Across GraphQL Resolvers

Batch Database Requests with a GraphQL API

Refactor the Data Loader into a Reusable Class

Create a New Cache on Every GraphQL Request Using Apollo Context

Install the DataLoader Package

Fetching an Item by ID with a GraphQL DataLoader

Fetching Many Items by Key with GraphQL DataLoaders

Count the Items in a Collection By Reusing a Data Loader

Count the Items in a Collection with a Custom Data Loader

Use GraphQL Data Loaders to Prevent Scaling Issues by Batching & Caching Database Requests

If users will be often querying the number of comments without also querying the list of comments

Then fetching the entire comment collection is wasteful. It's also not compatible with any pagination features that don't return the entire collection.

In this lesson, we will create a custom Data Loader specifically for counting items

https://app.egghead.io/api/v1/lessons/apollo-count-the-items-in-a-collection-with-a-custom-data-loader/subtitles

Instructor: [0:00] If users will often be querying the number of comments without also querying the list of comments, then fetching the entire comment table is wasteful. It's also not compatible with any pagination we might add later since we still need the total count.

[0:14] We can give it a dedicated comment count by post idLoader that selects post ID, counts post ID, groups by post ID, where a post ID is in keys, then maps each key to the count for that post ID, or zero if there were none. Update the resolver to use the new loader.

[0:47] You can run the query again, but it will show the same output as before.

Count the Items in a Collection with a Custom Data Loader

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Use GraphQL Data Loaders to Prevent Scaling Issues by Batching & Caching Database Requests