Express app.param issue with res.send

Question

I am trying to send a response but I am not quiet sure how to do that. I get this error Can't set headers after they are sent when I try to run "res.send or res.response" this code.

The way am I am creating my routes is that if /id is been entered then I will do a SQL query to check for the existence of that id in TableA. If the id exists then I will get the item eg. food, in the table_type column corresponding to that id. Then I will go to that table_type item named table eg. Food, and I will get the attributes from that table and send a response or render a page.

// parameter middleware that will run before the next routes
app.param('num', function(req, res, next, num) {
  var array = [];
  var id;
  var table;
  client.connect(function(err) {
    if(err) {
      return console.error('could not connect to postgres', err);
    }
    client.query("SELECT id, table_type FROM TableA WHERE id=" + num, function(err, result1) {
      if(err) {
        return console.error('error running query', err);
      }
      else {
        //console.log("###### THIS IS IT!!! #######");
        //console.log(result1);
        id = result1.rows[0].id;
        table = result1.rows[0].table_type.trim();

        var latitude;
        var longitude;
        if (table === "Food") {
          var name;
          var description;
          client.query("SELECT name, description, quantity, color FROM FoodTable WHERE item_id=" + id, function(err, result2) {
            if(err) {
              return console.error('error running query', err);
            }
            else {
              name = result2.rows[0].name.trim();
              description = result2.rows[0].description.trim();
              quantity = result2.rows[0].quantity.trim();
              color = result2.rows[0].color.trim();
              array.push(name, description, quantity, color);
              console.log(array);
              //---- WHY NO WORK? ------
              res.send(array);
            }
            client.end();
          });
        }
      }
      client.end();
    });
  });
  next();
});

Worded Explaination of the code: I am trying to write routes that would check if id exists in TableA using the app.param by calling the SQL query client.query . I cannot use the variables outside the function since the data will not be referenced once the function call is complete. So I have concatenated my query. So once the id exists in TableA I store the id and table_type into a variable and check the type in the if statement. So if the table type was Drinks then I would look in Drinks table to get the attributes associated with the id.

Answer 1

You are calling next() outside the asynchronous database call. So what happens is that next has already been executed and returned a response to the request hence headers have already been set when res.send method is called.