如何将子查询添加到带有轴的查询结果中

Question

I am querying an objects table based no an id . Then I want to query the same table with the id of my result and add it result object as a new property. Hope, that makes sense:

app.get(`/details`, (req, res) => {
  const { id } = req.query;
  connection.query(
    `SELECT
      objects.*
    FROM objects
    WHERE id = ${id}
    LIMIT 1`,
    (err, results) => {
      if (err) {
        return res.send(err);
      } else {
        let result = results[0];
        result.relationships = [];
        connection.query(
          `SELECT
            objects.*
          FROM objects
          WHERE relationship = ${result.id}`,
          (err, rel_results) => {
            if (err) {
              return res.send(err);
            } else {
              rel_results.forEach((el) => {
                result.relationships.push(el);
              });
              // This log looks fine. result.relationhips is an array of objects.
              console.log(result);
            }
          }
        );
        // Here, the result has an empty array for result.relationhips
        return res.json(result);
      }
    }
  );
});

When you look at the comments, why is the result correct in the log but not in the return?

Answer 1

You need to place the return statement within the nested callback, this is main because of early return:

result.relationships = [];
        connection.query(
          `SELECT
            objects.*
          FROM objects
          WHERE relationship = ${result.id}`,
          (err, rel_results) => {
            if (err) {
              return res.send(err);
            } else {
              rel_results.forEach((el) => {
                result.relationships.push(el);
              });
              // This log looks fine. result.relationhips is an array of objects.
              console.log(result);
              return res.json(result);
            }
          }
        );
       

Answer 2

You dont acutally have to build a promise. You can simply send your results when they are available within your second query callback:

(err, results) => {
  if (err) {
    return res.send(err);
  } else {
    let result = results[0];
    result.relationships = [];
    connection.query(
      `SELECT
        objects.*
      FROM objects
      WHERE relationship = ${result.id}`,
      (err, rel_results) => {
        if (err) {
          return res.send(err);
        } else {
          rel_results.forEach((el) => {
            result.relationships.push(el);
          });
          // This log looks fine. result.relationhips is an array of objects.
          console.log(result);

          res.json(result);
        }
      }
    );
  }