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QuestionUse async function to retrieve data while looping through from another function to insert objects Pin
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AnswerRe: Use async function to retrieve data while looping through from another function to insert objects Pin
Jeremy Falcon12-Jan-23 8:44
professionalJeremy Falcon12-Jan-23 8:44 
Couple things to consider here. First and foremost, do not use successive round trips in an API call as your first solution. It's always a last resort. It's much quicker to doing a JOIN on you indexes to combine the data. Yes this first payload be larger, but you only need to establish the connection once and you're still using the same sized payload even if it's split up into calls. So, the proper solution is to use a query or view and return that info to the client (the client being the Express server in this instance) in one trip... you can paginate if you need to break up the payload size into several calls.

To answer your question, and I do not suggest you do that this at all, but to address it...

In your doQuery function, notice that only the reject case in returned in your closure. Not the cause of your issue, but to be consistent. Also, the function doesn't need to return an explicit promise. It's being done already under the hood. Use try/catch in your async functions to handle error conditions. The syntax is much cleaner.
JavaScript
async function doQuery(query, params = []) {
  try {
    return await new Promise((resolve, reject) => {
      db.query(query, params, (err, rows) => {
        if (err)
          reject(err);
        else
          resolve(rows);
      });
    });
  } catch {
    return [];
  }
}
If your data is still null after reworking that routine than make sure db.query is returning valid data.

Also, if you plan on making successive calls like this, you'd be much, much better off using generators . But, that is a last choice. You should be redoing your DB design and queries first.
Jeremy Falcon

AnswerRe: Use async function to retrieve data while looping through from another function to insert objects Pin
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