Get the result of postgres-query as variable in nodejs

Question

I know that the following code prints the result of my query on the command line:

query.on("row", function (row, result) {
  result.addRow(row);
});

query.on("end", function (result, callback) {
    println(JSON.stringify(result))
});

However, I want to use the result value in the following code as a variable and not just have it printed out to the command line.

Update: Being able to use the values for the next query is not enough, I want it to be outside of the query scope:

query.on("row", function (row, result) {
  result.addRow(row);
});

query.on("end", function (result, callback) {
    println(JSON.stringify(result))
});
//use the result here

Thanks in advance for your answers.

Answer 1

You have 2 options:

• If you want to continue using the basic driver, you will have to use the result callback, and then nest those in order to use result in the next query:

  connection.query(query1, values1, function(err1, result1) {
      // check if(err1) first, then:
      connection.query(query2, values2, function(err2, result2) {
          // check if(err2) first, then:
          connection.query(query3, values3, function(err3, result3) {
              // check if(err3) first, then:
              cb(result1, result2, result3);        
          });
      });
  });
  

• The alternative approach is to use promises (pg-promise) when you can chain calls like this:

  db.query(query1, values2)
      .then(data => {
          return db.query(query2, values2);
      })
      .then(data => {
          return db.query(query3, values3);
      })
      .catch(error => {});
  

Although the right approach for pg-promise in this case is via method task:

db.task(t => {
    const result = {};
    return t.query(query1, values1)
        .then(data => {
            result.a = data;
            return t.query(query2, values2);
        })
        .then(data => {
            result.b = data;
            return t.query(query3, values3);
        });
        .then(data => {
            result.c = data;
            return result;
        });
})
    .than(data => {
        // data = {a, b, c}
    })
    .catch(error => {});

The second approach automatically gives you access to the modern syntax of ES6 and ES7 when executing multiple queries at a time, as you can do:

For ES6:

db.task(function * (t) {
    let a = yield t.query(query1, values1);
    let b = yield t.query(query2, values2);
    let c = yield t.query(query3, values3);
    return {a, b, c};
})
    .than(data => {
        // data = {a, b, c}
    })
    .catch(error => {});

For ES7 / Babel:

db.task(async t => {
    let a = await t.query(query1, values1);
    let b = await t.query(query2, values2);
    let c = await t.query(query3, values3);
    return {a, b, c};
})
    .than(data => {
        // data = {a, b, c}
    })
    .catch(error => {});