Craft GraphQL APIs in Elixir with Absinthe

Understanding the Problem

Anytime we need to do something like load an Ecto schema has_many association in a resolver, then query child values, we can quickly find ourselves mired in what’s referred to as the “N + 1 problem” and performing more database work than we expect. Let’s say you want to get the category for a bunch of menu items. The best way to go is to collate all the category_id values found within your set of menu items and then do a single SQL query for categories with those IDs. The N+1 problem happens when instead, you do an SQL query for each individual menu item’s category; this is where the problem gets its name. There’s 1 query to get the menu items themselves, and then N queries afterward, where N is the number of menu items. ...