True - but the important point worth discussing here is that most common GraphQL implementations make it really hard to think in joins.

The resolver pattern and data loader pattern make joins really painful.

eg: implement a simple top-N query (fetch 10 users and the most recent 5 articles for each) in GraphQL with a resolver tree, or even data loader.

> eg: implement a simple top-N query (fetch 10 users and the most recent 5 articles for each) in GraphQL with a resolver tree, or even data loader.

A most_recent_articles view?

query {

  Users (first: x) {

    …,

    articles (first: y, sortBy: CREATED) {

    ..

    }

  }

}

How would one implement the users and articles resolvers - that would be as efficient as a most_recent_views in sql?

- Resolver for the most recent articles

- Resolver for n users by ID

- Caching layer

This will be quite performant in general since in worst case we do 2 SQL queries but in most cases we hit a cache.

The problem is that it’s hard to get the articles resolver make one query to fetch all the recent articles. So you’ll end up with n+1 fetches from the db.

In the articles resolver, you have to:

Select from articles order by created where article.user_id = X limit 5.

And you’ll have to run this statement n times - once for each user.

Not sure how a data-fetching cache layer at the app server layer will help here.

@alex_lav: Your SQL query here is exactly what I meant! In SQL, this is easy, both to write and to optimize perf.

Implementing this with GraphQL resolvers (how folks typically write GraphQL servers) is hard - there's a users function and an articles function that are both called, so it's hard to implement those 2 functions contributing together towards a query plan. This was my point.

In fact a REST endpoint that takes a list of users and runs this query with the `IN` part parameterized is easier to build here. But the GraphQL version is a pain.

Sorry, I feel like there must be something I'm not understanding about the limitation you're trying to convey.

WITH relevant_users AS (

  SELECT id FROM users WHERE id IN (1)

)

SELECT users.name, mra.title

FROM users

INNER JOIN most_recent_articles mra

ON users.id = mra.user_id

INNER JOIN relevant_users

ON users.id = relevant_users.id;

This is a single query that can fetch users filtered by the First: (although I just did in, you could add whatever filtering options you wanted in the relevant_users cte) with the most recent articles view we've discussed previously.

Lateral JOIN