Javascript Array of object value into multidimensional array

Question

I am in process of learning expressJS with NodeJS.

I am trying to insert multiple rows into mySQL table. Since the bulk insert query requires data like

[["a",1], ["b",2], ["c",3]]

How can I transform my array of objects to such form? Here is my JSON post data

[
 {
    "productID" : 1,
    "stock": -3
 },
 {
    "productID" : 1,
    "stock": 5
 }
]

How to tranform such JSON object into the multidimensional array?

[[1,-3],[1,5]]

Here is what I have tried so far.

let promises = []
req.body.map((n) => {
  promises.push(new Promise(resolve => {
    let { productID, stock } = n
    let values = {
      PRODUCT_ID: productID,
      STOCK: stock
    }
    let sql = 'INSERT INTO product_stock_history SET ?'
    db.connection.query(sql, values, (err, results) => {
      if (err) {
        console.log("Failed to add stocks record: " + err)
        res.sendStatus(500)
        return
      } else {
        res.send("Stock record has been added")
      }
    })
  }))
})

The above code is working, but in the end I have error with the mySQL syntax which I believe something to do with the promise. I am not familiar with the promise :)

Error: Can't set headers after they are sent.

So what i want to achieve is just the mapping without Promise.

thanks

Hi, thank you so much for the input! :) I have edited the question with codes that I have tried. Sorry for the inconvenience caused — Alvin
– Alvin, Commented Jan 22, 2019 at 9:20

adiga · Accepted Answer · 2019-01-22 09:16:50Z

3

You could pass Object.values as parameter to map like this:

const input = [
 {
    "productID" : 1,
    "stock": -3
 },
 {
    "productID" : 1,
    "stock": 5
 }
]

const output = input.map(Object.values)
console.log(output)

answered Jan 22, 2019 at 9:16

adiga

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