dataloader VS mocha

When I began working with GraphQL, I had concerns about the N+1 query problem. In my research, I came across the DataLoader pattern and its implementation on GitHub. While I explored various examples of its usage, I still struggled to grasp how it operates internally. Join me in delving a bit deeper into GraphQL DataLoader! :)

DataLoader: it is the standard solution to N+1 problem.

Additionally, you can use DataLoader or similar tools to optimize data fetching and avoid over-fetching or under-fetching data. Ultimately, performance and load tests ensure that your GraphQL API delivers optimal performance, meets response time expectations, and provides a smooth experience for users, even under heavy loads.

The most common practice is to turn N+1 into 1+1 using dataloaders (https://github.com/graphql/dataloader for JS, there are equivalents for most implementations). The N resolvers invoke a single batched loader which receives a list of keys and returns a list of values.

Let's take Payload, for example. Surprise, surprise. We have a relationship field, and it can store IDs to other related documents which are seamlessly merged in when you retrieve documents from the DB. We leverage the dataloader pattern to batch together all "populations" required for a given query, returning them all super fast and with as few separate queries to the DB as possible. We actually even outperform SQL-based frameworks quite a bit. In a purely relational test, we were 3x faster than Directus and 7x faster than Strapi while both were running Postgres, and we were on MongoDB.

Also, have a look at Facebook's Dataloader[0].

[0] https://github.com/graphql/dataloader

In the next article, I'm going to implement a GraphQL server with dataloader using the tools we introduced.

The one example of using Scoped dependency that comes to my mind, it's HTTP request level caching for libs like dataloader.

you would fetch these 1000 rows via dataloader that batches all requests for this relation to a single query... solving the n+1 issue

Using something like Vitest, Jest, or Mocha didn't work because:

MochaJS is a feature-rich JavaScript test framework running on Node.js, making it a popular choice for both backend and frontend testing. It's known for its flexibility and straightforward syntax, allowing for asynchronous testing and the use of any assertion library.

We use Jest Framework for testing. Jest is not a dogma, and, of course, in its place can be any other test runner, such as Mocha or Ava. Let's focus on tests. I'll provide a short example because I don’t want to waste your time. You can find the full version here. It's crucial to read the comments in the code below. Let's go!

JavaScript Popular tools for testing: Mocha, Jasmine, Unit JS, Jest

To execute your tests, you can create test scripts using popular testing frameworks like Mocha, Jasmine, or Jest. These frameworks provide a structured way to organize and run your tests, report results, and handle assertions.

⚗️ Mocha and Chai for testing

Testing frameworks like Jest, Mocha, and Jasmine are crucial for software development, ensuring code reliability and correctness. They offer features like test suites, test cases, assertions, and asynchronous testing support.