transaction-controller.js

const router = require('express').Router();
const { Product } = require('../models/')

router.post('order', (req, res) => {
  try {
    let outOfStock = {
      bool: false,
      data: []
    }
    let allProduct = await Product.findAll({
      where: {
        id: {
          in: req.body.items.map(el => el.id)
        }
      },
      attributes: ['id', 'stock']
    })
    allProduct = allProduct.map(el => {
      if (el.stock < req.body.items.find(inner => inner.id === el.id).item) {
        outOfStock.bool = true
        outOfStock.data.push(el)
      }
      return {
        id: el.id,
        stock: el.stock
      }
    })

    //validation
    if (req.body.items.length > allProduct.length) {
      const notFound = req.items.length.filter(el =>
        allProduct.find(inner => inner.id === el.id)
      )
      const error = {
        errorMsg: 'Product not found',
        data: notFound
      }
      return res.json(error)
    }
    if (outOfStock.bool) {
      return res.json({
          errorMsg: 'Stuff out of Stock',
          data: outOfStock.data
        })
      )
    }
    await Promise.all(
      allProduct.map(el => {
        return Product.update(
          {
            stock:
              el.stock - req.body.items.find(inner => inner.id === el.id).item
          },
          {
            where: {
              id: el.id
            },
            transaction
          }
        )
      })
    )
    res.json({isOk:true})
  } catch(err) {
    res.status(500).json({
      isError: true,
      err
    })
  }
})

module.exports = router