N+1 Problem & DataLoaderIntermediate
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javascriptWhat is the N+1 Problem in GraphQL and how does DataLoader solve it?
Explanation & Concept
The N+1 problem occurs when a query fetches 1 parent record and then executes N individual database queries for related child records in field resolvers.
**DataLoader** solves this by batching and caching: it collects all individual IDs requested within a single event loop tick and fires a single batch query (`SELECT * FROM table WHERE id IN (...)`).
Code Example
javascript
import DataLoader from "dataloader";
// Batch function: receives array of author IDs and returns array of authors in identical order
const authorLoader = new DataLoader(async (authorIds) => {
const authors = await db.authors.findMany({
where: { id: { in: authorIds } }
});
// Map back to match input authorIds order
return authorIds.map((id) => authors.find((a) => a.id === id));
});
// Inside GraphQL Resolver:
export const resolvers = {
Book: {
author: (book) => authorLoader.load(book.authorId) // Batched automatically!
}
};How It Works & Key Takeaways
DataLoader collapses 100 separate database queries for 100 books into a single `WHERE id IN (...)` query, dramatically reducing database load.
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