How to execute nested queries within async and conditional loop in node.js

Question

I am using node.js,express and postgres db for my project. I have few queries in async function which I am not able to execute in a sequence. sample code for reference.

for(let i=0;i<person_size;i++)
{
    var check_person_query="select per_id_pk from person_tbl where per_fname='"+person_fname[i]+"' and per_lname='"+person_lname[i]+"'";

    dbClient.query(check_person_query,function(err,result){
        if(result.rows.length>0)
        {
            console.log("Call: 1.1");
            console.log("person already exists");
        }
        else
        {
            var insert_person_query = "insert into person_tbl (per_fname,per_lname,per_gender,profile_photo) values('"+person_fname[i]+"','"+person_lname[i]+"','"+person_gender[i]+"','profile_photo_link')";
            //console.log("query2: "+insert_person_query);
            dbClient.query(insert_person_query,function(err,result){
                    if (err) throw err;
                    console.log("Call: 1.2");
                    console.log("New person has been added");       
            });

            var fullname = person_fname[i].concat(person_lname[i]);
            low_fullname = fullname.toLowerCase();

            person_pic[i].mv("/home/aniket/content_info/images/"+low_fullname+".jpg", function(err){
                if (err) throw err;
            });                                             
        }
    });
}//end for

In above code, when if condition fails, the else part gets executed in the very end of my async.series function. As long as if condition succeeds, everything works perfectly in sequential manner. How to sequentially run nested db queries? I have used async.waterfall but still no expected output.

UPDATE: (SOLVED)

Instead of using nested query functions, I removed the nesting, and prepared a single query so that I would obtain an expected result and maintain the execution sequence.

You can always use promises and async/await, the latter naturally works with loops. — Estus Flask

vkarpov15 vkarpov15 · Accepted Answer · 2018-06-19T15:18:12

You should really just use async/await. The pg lib supports promises, so you can just do this:

for(let i=0;i<person_size;i++) {
  const result = await dbClient.query(check_person_query);
  if(result.rows.length <= 0) {
    await dbClient.query(insert_person_query);
  }
}

Here's some more info on using for loops with async/await.

How to execute nested queries within async and conditional loop in node.js

2 Answers