SQL.md

Using DataLoader with SQLite

While not a key-value store, SQL offers a natural batch mechanism with SELECT * WHERE IN statements. While DataLoader is best suited for key-value stores, it is still suited for SQL when queries remain simple. This example requests the entire row at a given id, however your usage may differ.

const DataLoader = require('dataloader')
const sqlite3 = require('sqlite3')

const db = new sqlite3.Database('./to/your/db.sql')

// Dispatch a WHERE-IN query, ensuring response has rows in correct order.
const userLoader = new DataLoader(ids => new Promise((resolve, reject) => {
  db.all('SELECT * FROM users WHERE id IN $ids', {$ids: ids}, (error, rows) => {
    if (error) {
      reject(error);
    } else {
      resolve(ids.map(
        id => rows.find(row => rows.id === id) || new Error(`Row not found: ${id}`)
      ));
    }
  });
}));

// Usage

const promise1 = userLoader.load('1234')
const promise2 = userLoader.load('5678')
const [ user1, user2 ] = await Promise.all([promise1, promise2])
console.log(user1, user2)