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* DataLoader Pattern Utilities
*
* Provides batch loading functions to efficiently load related data
* and avoid N+1 query problems. These loaders batch multiple requests
* into single database queries.
*/
import { prisma } from '@/lib/prisma';
import type { Category, Product } from '@prisma/client';
/**
* Simple batching function that collects requests and executes them together
* This is a lightweight alternative to the dataloader library
*/
type BatchLoadFn<K, V> = (keys: readonly K[]) => Promise<(V | null)[]>;
interface Loader<K, V> {
load: (key: K) => Promise<V | null>;
loadMany: (keys: K[]) => Promise<(V | null)[]>;
clear: (key: K) => void;
clearAll: () => void;
}
function createBatchLoader<K, V>(batchFn: BatchLoadFn<K, V>): Loader<K, V> {
const cache = new Map<K, Promise<V | null>>();
let batch: K[] = [];
let batchPromise: Promise<void> | null = null;
const executeBatch = async () => {
const currentBatch = [...batch];
batch = [];
batchPromise = null;
if (currentBatch.length === 0) return;
const results = await batchFn(currentBatch);
currentBatch.forEach((key, index) => {
const existingPromise = cache.get(key);
if (existingPromise) {
// The promise is already set, need to resolve it
// This is handled by the batchFn returning results in order
}
// Update cache with resolved value
cache.set(key, Promise.resolve(results[index]));
});
};
const scheduleBatch = () => {
if (!batchPromise) {
batchPromise = Promise.resolve().then(executeBatch);
}
return batchPromise;
};
return {
load: async (key: K): Promise<V | null> => {
const cached = cache.get(key);
if (cached) return cached;
const promise = new Promise<V | null>((resolve) => {
batch.push(key);
scheduleBatch().then(async () => {
const results = await batchFn([key]);
resolve(results[0]);
});
});
cache.set(key, promise);
return promise;
},
loadMany: async (keys: K[]): Promise<(V | null)[]> => {
const results = await batchFn(keys);
keys.forEach((key, index) => {
cache.set(key, Promise.resolve(results[index]));
});
return results;
},
clear: (key: K) => {
cache.delete(key);
},
clearAll: () => {
cache.clear();
}};
}
/**
* Create a category loader that batches category lookups
*/
export function createCategoryLoader(): Loader<number, Category> {
return createBatchLoader<number, Category>(async (ids) => {
const categories = await prisma.category.findMany({
where: { id: { in: [...ids] } }});
const categoryMap = new Map(categories.map(c => [c.id, c]));
return ids.map(id => categoryMap.get(id) || null);
});
}
/**
* Create a review count loader that batches review count lookups
*/
export function createReviewCountLoader(): Loader<number, number> {
return createBatchLoader<number, number>(async (productIds) => {
const counts = await prisma.review.groupBy({
by: ['productId'],
where: {
productId: { in: [...productIds] }},
_count: true});
const countMap = new Map(counts.map(c => [c.productId, c._count]));
return productIds.map(id => countMap.get(id) ?? 0);
});
}
/**
* Create a review average loader that batches average rating lookups
*/
export function createReviewAverageLoader(): Loader<number, number> {
return createBatchLoader<number, number>(async (productIds) => {
const averages = await prisma.review.groupBy({
by: ['productId'],
where: {
productId: { in: [...productIds] }},
_avg: { rating: true }});
const avgMap = new Map(averages.map(a => [a.productId, a._avg.rating ?? 0]));
return productIds.map(id => avgMap.get(id) ?? 0);
});
}
/**
* Create a product loader that batches product lookups
*/
export function createProductLoader(): Loader<number, Product> {
return createBatchLoader<number, Product>(async (ids) => {
const products = await prisma.product.findMany({
where: { id: { in: [...ids] } }});
const productMap = new Map(products.map(p => [p.id, p]));
return ids.map(id => productMap.get(id) || null);
});
}
/**
* Load products with their categories and review statistics
* This is an optimized version that avoids N+1 queries
*/
export async function loadProductsWithStats(
productIds: number[]
): Promise<Array<{
product: Product;
category: Category | null;
reviewCount: number;
averageRating: number;
}>> {
if (productIds.length === 0) return [];
// Execute all queries in parallel
const [products, categories, reviewCounts, reviewAverages] = await Promise.all([
// Get products
prisma.product.findMany({
where: { id: { in: productIds } }}),
// Get categories for these products
prisma.category.findMany({
where: {
products: {
some: { id: { in: productIds } }}}}),
// Get review counts
prisma.review.groupBy({
by: ['productId'],
where: { productId: { in: productIds } },
_count: true}),
// Get average ratings
prisma.review.groupBy({
by: ['productId'],
where: { productId: { in: productIds } },
_avg: { rating: true }}),
]);
// Build lookup maps
const categoryMap = new Map(categories.map(c => [c.id, c]));
const countMap = new Map(reviewCounts.map(c => [c.productId, c._count]));
const avgMap = new Map(reviewAverages.map(a => [a.productId, a._avg.rating ?? 0]));
// Combine results
return products.map(product => ({
product,
category: categoryMap.get(product.categoryId) ?? null,
reviewCount: countMap.get(product.id) ?? 0,
averageRating: avgMap.get(product.id) ?? 0}));
}
/**
* Load user's order statistics efficiently
*/
export async function loadUserOrderStats(
userIds: number[]
): Promise<Map<number, { orderCount: number; totalSpent: number }>> {
if (userIds.length === 0) return new Map();
const stats = await prisma.order.groupBy({
by: ['userId'],
where: { userId: { in: userIds } },
_count: true,
_sum: { total: true }});
return new Map(
stats.map(s => [
s.userId,
{
orderCount: s._count,
totalSpent: s._sum.total ?? 0},
])
);
}
/**
* Load category tree with product counts efficiently
*/
export async function loadCategoryTree(): Promise<Array<{
category: Category;
productCount: number;
children: Array<{ category: Category; productCount: number }>;
}>> {
// Get all categories with product counts in a single query
const categories = await prisma.category.findMany({
include: {
_count: { select: { products: true } },
children: {
include: {
_count: { select: { products: true } }}}},
where: { parentId: null }, // Only top-level categories
});
return categories.map(cat => ({
category: {
id: cat.id,
title: cat.title,
slug: cat.slug,
imageUrl: cat.imageUrl,
description: cat.description,
createdAt: cat.createdAt,
parentId: cat.parentId},
productCount: cat._count.products,
children: cat.children.map(child => ({
category: {
id: child.id,
title: child.title,
slug: child.slug,
imageUrl: child.imageUrl,
description: child.description,
createdAt: child.createdAt,
parentId: child.parentId},
productCount: child._count.products}))}));
}
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