(node/express) 从数据库查询中收集多条数据并发送到 index.ejs？

Question

I'm obtaining multiple pieces of info from a postgres database and using them to render a web page via express in node.

I can make a single query of the "measurements" database and pass it in no problem eg:

    pool.query("SELECT * from measurements", (err, result) => {
  if(err) {
    throw err;
  } else {
    var set1= JSON.stringify(result);
    app.get("/", (req, res) => { res.render("index", { set1: set1}); });
  }
});

My issue is making multiple queries and rendering them all together. At first I tried to store the query results in separate variables outside of a function and passing all of them like so:

var set1= pool.query("SELECT * from measurements");
var set2= pool.query("DIFFERENT QUERY* from measurements");

app.get("/", (req, res) => { res.render("index", { set1: set1, set2: set2 }); });

but that didn't work because of promises/synchronous method (I think) because it just tells me it's awaiting a promise (or something like that, I can't quite remember). I tried to use some await stuff as a fix but nothing worked. (or I wasn't implementing correctly)

So what's the best way to do this? I thought about either:

1. build a function that makes all the necessary queries, declares the variables, and then renders the page at the end using all of them (I think this is where await/async works?)

2. somehow combining all the query results into a single object and just sending that single object with all the data, then sorting/classifying/displaying it on the client side. (or just sending the whole database to the client, but that seems like a bad idea)

but I'm not exactly sure the best way to do either of these. Any help would be appreciated, am new to JS

Answer 1

Well doing it with async / await is pretty straight forward:

app.get("/", async (req, res) => {
  var set1 = await getMeasurments("SELECT * FORM BLABLA");
  var set2 = await getMeasurments("SELECT * FORM BLABLA");
  res.render("index", { set1, set2 });
});

function getMeasurments(query) {
  return new Promise((res, rej) => {
    pool.query(query, (err, result) => {
      if (err) {
        rej(err);
      } else {
        res(result);
      }
    });
  });
}

Just make a new function and promisfy it

Answer 2

const query = async(query) => {
  const client = await pool.connect()
  const result = await client.query(query)
  client.release()
  return result; 
})

const requests = [
    query("SELECT * from measurements"), 
    query("DIFFERENT QUERY* from measurements")
]
Promise.All(requests).then(results => {
    return results.reduce((acc, curr) => {
        return Object.assign(acc, curr)
    }, {})
}).then(data => {
   res.render("index", data)
})

Answer 3

Taking your initial code, you can, first (1), promisify the pool.query and then (2) call it with await inside an async function; and (3) use the composed function in you get route

const poolquery = util.promisify(pool.query);   // (1)

async function renderindex(req,res) {   // (2)
  try {
    let set1 = await poolquery ("SELECT * FROM SET1 ...");
    let set2 = await poolquery ("SELECT * FROM SET2 ..."); 
    res.render("index", { set1, set2 });
  } catch (err) {
    res.status(500).send(err);
  }
}

app.get("/", renderindex);   // (3)