Sequelize Dataloader Advices

advise-find-dataloader.js

/**
 * @overview    Sequelize find - dataloader advice
 * @author      Richard Ayotte
 * @copyright   Copyright © 2017 Richard Ayotte
 * @date        2017-11-03
 * @license     GNU GPL-3.0
 * @flow
 */

'use strict'
const DataLoader = require('dataloader')
const hash = require('object-hash')
const {
	find
	, get
	, isPlainObject
	, union
} = require('lodash')
const {Op} = require('sequelize')

const log = require('../../lib/log')
const loaders = new Map()

const symbolKeysToStrings = obj => {
	const newObj = {}
	Object.getOwnPropertySymbols(obj).forEach(k => {
		newObj[String(k)] = isPlainObject(obj[k]) ? symbolKeysToStrings(obj[k]) : obj[k]
	})
	Object.keys(obj).forEach(k => {
		newObj[k] = isPlainObject(obj[k]) ? symbolKeysToStrings(obj[k]) : obj[k]
	})
	return newObj
}

module.exports = function adviseDataloader({args, proceed, proceedCount, target}) {
	const [options, transaction] = args
	const where = get(options, 'where')
	let id

	// Don't dataload when there's not where.
	if (!where) {
		return proceed()
	}

	const whereKeys = [
		...Object.keys(where)
		, ...Object.getOwnPropertySymbols(where)
	]

	// Don't dataload if 'or' is found in the where keys.
	if (whereKeys.includes(Op.or) || whereKeys.includes('$or')) {
		return proceed()
	}

	// Only look into the where object 1 level deep. I don't think I'll need to
	// go much deeper so leaving the recursive complexity out for now. RA
	if (whereKeys.includes('id')) {
		id = where.id
		delete where.id
	}
	else if (whereKeys.includes(Op.and)) {
		if (!where[Op.and].id) {
			return proceed()
		}
		id = where[Op.and].id
		delete where[Op.and].id
	}

	if (!id) {
		return proceed()
	}

	// Create a new where object with all the Symbols transformed into strings.
	const loaderWhere = symbolKeysToStrings(where)

	const loaderId = hash(
		JSON.stringify({
			attributes: options.attributes
			, include: options.include
			, table: target.tableName
			, where
		})
		, {
			encoding: 'binary'
		}
	)

	let loader = loaders.get(loaderId)

	if (!loader) {
		loader = new DataLoader(function(keys) {
			return proceed({
				meta: options.meta
				, attributes: union(['id'], options.attributes)
				, where: {
					[Op.and]: {
						id: [...new Set(keys)]
						, ...where
					}
				}
			})
			.then(sqlResult => {
				return keys.reduce((result, key) => {
					result.push(find(sqlResult, {id: key}))
					return result
				}, [])
			})
		}, { cache: false })

		loaders.set(loaderId, loader)
	}

	return loader.load(id)
}