Nodejs Mysql asynchronous-CodePudding

I'm trying to return my users list from my Mysql database through this endpoint.

The problem is that it return "undefined".

Do you know how to solv this?

Thx in advance :)

app.get("/users", async (req, res) => {
  users = await query_my_users_from_db()
  // Got "users = undefined" here
  console.log(users)
  return JSON.stringify(users)
})

async function query_my_users_from_db() {
  var users = await db.query("SELECT * FROM `users`", function (err, result) {
    if (err) throw err
    users = Object.values(JSON.parse(JSON.stringify(result)))
    return users
  })
}

CodePudding user response：

Since db.query is callback based, you should change your code into:

function query_my_users_from_db(callback) {
   db.query("SELECT * FROM `users`", callback)
}

remove all the async\await since you are not using any promises!

then define your callback

const usersHandler = (err, result) => {
 ... do what you want with your users ...
}

and use it like this:

query_my_users_from_db(usersHandler)

Another option is to use some promise-based wrapper package for MySQL, there is plenty or use node util.promisify() (https://www.geeksforgeeks.org/node-js-util-promisify-method/) and then use async\await and remove the callback altogether.

Hope that it helps

CodePudding user response：

I used this and it's working like a charm.

db.promise = (sql, params) => {
      return new Promise((resolve, reject) => {
        db.query(sql, params, (err, result) => {
          if (err) {
            reject(new Error())
          } else {
            resolve(result)
          }
        })
      })
    }

    async function connection(query) {
      const result = await db.promise(query)
      return result
    }

    app.get("/users", async (req, res) => {
      users = await connection("SELECT * FROM `users`")
      return users
    })