Node.js and Heroku, how to insert a second query?

Question

I am working with Node.js and Heroku; and I have a question about the following code, that I found online:

app.get('/db', function (request, response) {
  pg.connect(process.env.DATABASE_URL, function(err, client, done) {
    client.query('SELECT * FROM test_table', function(err, result) {
      done();
      if (err)
       { console.error(err); response.send("Error " + err); }
      else
       { response.render('pages/db', {results: result.rows} ); }
    });
  });
});

This lists the contents of the test_table table, but I also want to perform the following query:

*"INSERT INTO test_table (fieldOne, fieldTwo) VALUES (MAX(fieldOne)+1, MAX(fieldTwo) 2)"

How can I integrate this in the code above?

Here is something I tried, but with no success:

app.get('/db', function (request, response) {
  pg.connect(process.env.DATABASE_URL, function(err, client, done) {
    client.query('SELECT * FROM test_table', function(err, result) {
      done();
      if (err)
       { console.error(err); response.send("Error " + err); }
      else { 
        response.render('pages/db', {results: result.rows} ); 
        client.query("INSERT INTO test_table  (id, name) VALUES (MAX(id)+1,'TEST')", function(err, result) {done();});
      }
    });
  });
});

I don't know if this last chunk of code is almost right or totally wrong. But all I can say is that the DB table (test_table) is not updated.

Answer 1

In case it might help someone else, I post here the change I made to have my code work:

app.get('/db', function (request, response) {
  pg.connect(process.env.DATABASE_URL, function(err, client, done) {
    client.query('SELECT * FROM test_table', function(err, result) {
      done();
      if (err)
       { console.error(err); response.send("Error " + err); }
      else { 
        response.render('pages/db', {results: result.rows} ); 
        client.query("INSERT INTO test_table  (id, name) VALUES ((SELECT MAX(id) FROM test_table)+1,'TEST')", function(err2, result2) {done();});
      }
    });
  });
});

There must be other things to be said about this, but at least it now works.

Answer 2

This answer is meant in case some developers trying to get their hands on Node.js hit the same questions I did. Here is a tiny site I made, as a use case, in order to get some practice. I am showing hereafter the relevant code. It will hopefuly help someone later.

Reading Getting Started on Heroku with Node.js I got my hands on the subject.

I started from this as suggested in the document mentioned above.

Here are the relevant changes I made to the top index.js file:

app.get('/', function (request, response) {
  pg.connect(process.env.DATABASE_URL, function(err, client, done) {
    client.query('SELECT * FROM Prime_List ORDER BY rank', function(err, result) {
      done();
      if (err)
       { console.error(err); response.send("Error " + err); }
      else { 
         client.query('SELECT * FROM Leap_List ORDER BY rank', function(err, resultLeap) {
           done();
           if (err) {console.error(err); response.send("Error " + err);}
           else {
             response.render('pages/index', {results: result.rows, resultsLeap:resultLeap.rows, ua:agent} );
             lastPrime=result.rows[result.rows.length-1].prime;
             newPrime=getNextPrime(result.rows);
             client.query("INSERT INTO Prime_List (rank,prime) VALUES ((SELECT MAX(rank) FROM Prime_List)+1,"+newPrime+")", 
             function(err, result2) {
              done();
              if (err){ console.error(err); response.send("Error " + err); }
              else {
                client.query("SELECT COUNT(*) FROM Leap_List WHERE (leap="+(newPrime-lastPrime)/2+")",
                function(err, resultCnt) {
                  done();
                  if (err) { console.error(err); response.send("Error " + err); }
                  else {
                    if (resultCnt.rows[0].count==1) {
                      client.query("UPDATE Leap_List SET count=count+1 WHERE (leap="+(newPrime-lastPrime)/2+")",
                        function(err, resultUpd) {
                          done();
                          if (err) { console.error(err); response.send("Error " + err); }
                      });
                    } else /*(resultCnt[0]==0)*/ {
                      leapQuery="INSERT INTO Leap_List (rank,leap,initial,final,count) VALUES";
                      leapQuery+=" ((SELECT MAX(rank) FROM Leap_List)+1,";
                      leapQuery+=(newPrime-lastPrime)/2+",";
                      leapQuery+=lastPrime+",";
                      leapQuery+=newPrime+",";
                      leapQuery+="1)";
                      client.query(leapQuery,
                      function(err, resultUpd) {
                        done();
                        if (err) { console.error(err); response.send("Error " + err); }
                      });
                    }}});
              }});
           }});
      }});
  });
});


function getNextPrime(primeList) {
  var resultPrime = primeList[primeList.length-1].prime + 2;

  do {for (i=1; i<primeList.length; i++) {
        if (primeList[i].prime*primeList[i].prime>resultPrime) return resultPrime;
        if (resultPrime%primeList[i].prime == 0) break;
      }
      resultPrime+=2;
  } while (true);
}

Here are the relevant modifications I made to the views/pages/index.ejs file (version using tables):

First table (the prime numbers):

<table cellspacing=5>
    <% var npr=15; i=0; results.forEach(function(r) {
        if ((i==90)&&(npr==15)) { npr--; i=0; %> </table><br/><table> <% }
        if ((i==70)&&(npr==14)) { npr--; i=0; %> </table><br/><table> <% }
        if (i%npr==0) { %> <tr align=right> <% } %>
        <td bgcolor=#FFFF66><%= r.rank %></td><td bgcolor=#66FF66><font color=#000080><%= r.prime %></font></td>
        <% if (i%npr==(npr-1)) { %> </tr> <% } %>
        <% i++; %>
    <% }); %>
</table>

Second table (the leaps):

<table cellspacing=5>
<tr align=center>
<td bgcolor=#FFAAFF>Rank</td><td bgcolor=#FFAAFF>Leap</td>
<td bgcolor=#FFAAFF>Count</td><td  bgcolor=#FFAAFF colspan=2>First case</td>
</tr>
    <% var npr=5; i=0; total=0;
      resultsLeap.forEach(function(r) { 
        total+=r.count; %>
        <tr align=right>
        <td bgcolor=#FFFF99><%= r.rank %></td>
        <td bgcolor=#EEDD88><font color=#000080><%= r.leap %></font></td>
        <td bgcolor=#EEDD88><font color=#000080><%= r.count %></font></td>
        <td bgcolor=#88EEDD><font color=#000080><%= r.initial %></font></td>
        <td bgcolor=#88EEDD><font color=#000080><%= r.final %></font></td>
       </tr>
        <% i++; %>
    <% }); %>
<tr align=right>
<td bgcolor=#FFAAFF colspan=2>Total :</td>
<td bgcolor=#FFAAFF><%= total %></td>
</tr>
</table>

Please leave advices or comments, concerning the way I did in the code above, if you happen to read this and be an expert in Node.js.