RESTless London - July 16, 2020

GraphQL N+1 Problem

tl;dr: The N+1 problem occurs when the server executes more round trips to the datastore for related or nested data than necessary resulting in inefficiencies and longer load times.

About Me

• Senior Frontend Software Engineer at Seaspan Corp
• Denver, CO
• Love travel, tennis, and being efficient
• mhooper72.com

Lets look at an example and see our data model?

We have an sqlite3 DB with sequalize for our ORM. It's 2 simple tables as seen below, one with SolarSystems that has a one-to-many relationship with Planets

SolarSystems

Has many planets

SELECT * FROM SolarSystems

#	id	name
1	1	Intuitive
3	3	Core

Planets

SELECT * FROM Planets

#	id	name	solarSystemId
1	1	Cambridgeshire	1
6	6	Functionality	3

Approaches:

Laissez-faire:

With this approach, we don't concern ourselves with much. We are getting back the data that we requested and we aren't asking any more questions about it. In the short run, with small data sets and few users, this approach will likely be adequate and no result in too much pain. We should look to be more thoughtful for any production application.

JOIN vs N+1

JOINs:

JOINs are common in SQL land. Here they are likely to be fast and performant just like other places where you use them. In GraphQL land, we can find ourselves fetching unessecary data if we aren't careful and the logic to conditionally create joins can become complex quickly.

To Join Or Not To Join

Dataloader:

DataLoader is a generic utility to be used as part of your application's data fetching layer to provide a simplified and consistent API over various remote data sources such as databases or web services via batching and caching.

Dataloader Package

Advanced:

GraphQL Batch Resolver

When do I use dataloader and when do I use graphql-resolve-batch?

• Does your field have arguments?
• Is it hard for you to derive a primitive value from your source values for your field?
• Do you not have the ability to add any new values to context? (such as in an embedded GraphQL schema)

Repo Info:

Clone: https://github.com/hoop71/RESTless-London

Start: yarn start || npm start

Installation:

From root, yarn || npm i

DB setup:

cd db

npx sequelize db:migrate

npx sequelize db:seed:all

Tools:

ORM: Sequelize

VSCode Extension: SQLTools