Making an async loop in node.js with sql - node.js

Question

Here is what I'm trying to do:
Start a looping (10x)
Select on sql to return 1 register (select top 1 where 'running' is null)
Sql update 'running' status to 'running'
If the record is null, I access an API and get some data
The result is updated on the initial sql record (set running = 'ok')
End looping (start over)
Thing is, node.js does not wait for start over, it does everything at the same time. That way, 'running' is always null.
var express = require('express');
var app = express();
var c_MyApi = require('./controller/call_MyApi');
var mongo = require('./controller/crud_mongo');
var c_email = require('./controller/api_email_verify');
var c_sql = require('./controller/consulta_sql');
var MyLink = '',
id = 0;
for( var i = 0 ; i < 10 ; i++){
c_sql.busca().then(function(res) {
MyLink = res[0].MyLink;
id = res[0].id;
c_sql.marca(id).then(
c_MyApi.busca(MyLink, function(a) {
if (a == 0) {
c_sql.atualiza(id, 'sem_email', 's/e');
}
if (a == 1) {
c_sql.atualiza(id, 'link_errado', 'l/e');
} else {
for (var i = 0; i < a.length; i++) {
var email = a[i].address;
c_email.busca(email, function(e_valid) {
c_sql.atualiza(id, email, e_valid)
})
}
}
})
)
})
}
}
//consulta_sql.js
var sql = require("seriate");
var search = function() {
var exec = 'select top 1 MyLink, id from sys_robo_fila where done is null';
sql.setDefaultConfig(config);
return sql.execute({
query: exec
});
}
var usado = function(id) {
var exec = "update sys_robo_fila set done = 'r' where id = " + id + "";
sql.setDefaultConfig(config);
return sql.execute({
query: exec
});
}
var update = function(id, email, valid) {
var exec = "update sys_robo_fila set email = '" + email + "' , validacao = '" + valid + "' , done = 'ok' where id = " + id + "";
sql.setDefaultConfig(config);
return sql.execute({
query: exec
});
}
module.exports = {
busca: search,
atualiza: update,
marca: usado
}
Any sugestions?

Answer 1

The call to c_sql.busca() is returning a Promise immediately and then continuing on to the next loop before then() is called, which is why they seem to run at the same time (they are actually just running very quickly, but before the Promise is resolved.
If you want this to run synchronously, one loop at a time, I would recommend using a recursive function to not start the loop again until the Promises have resolved.
let count = 0;
function doSomething() {
// this returns immediately, before .then() executes
return c_sql.busca()
.then(() => {
// do some more stuff after c_sql.busca() resolves
return c_sql.busca();
})
.then(() => {
// increment your count
count += 1
if (count<10) {
// less than 10 runs call the function again to start over
return doSomething();
}
});
}
This article might be helpful in understanding Promises: https://medium.com/#bluepnume/learn-about-promises-before-you-start-using-async-await-eb148164a9c8