node.js synchronous call gather results - node.js

Question

I have a table where Persons are saved an their time (in seconds) where they were active.
I would like to write a function that gathers the total time in another table called gather.
For each row I am checking if an entry in the gather table exists. Depending on that result I make an insert or an update.
db.serialize(function() {
db.each("SELECT * from TEST", function(err, row) {
db.get("SELECT * from GATHER where name = " + row.name "", function(err, row) {
if(row === undefined || row === null){
var stmt = db.prepare("INSTER INTO gather (name, time) VALUE(?,?)");
stmt.run([name, seconds], function(error){
console.log('lastInsert ' + this.lastID);
});
stmt.finalize();
}else{
seconds += row.time;//increment time
var stmt = db.prepare("UPDATE gather SET time = ? WHERE name = ?");
stmt.run([seconds, row.name], function(error){
console.log('lastInsert ' + row.idProcessed);
});
stmt.finalize();
}
});
});
});
The problem that I ecounter is that sqlite runs asynchronously. Therefore multiple entries are created in my gather table although lines should be updated.
What would be the right way to run this function sychronously? Should I limit the lines and call the function every second or is there a smarted way?

Answer 1

You could use async. For example (but first you should read final notes at the end):
var async = require('async');
var data = {}
var yourFirstSelect() = function(callback){
//You do your first select
//...
db.get("SELECT * from TEST", function(err, row) {
if(row){
data.name = row.name;
data.otherInterestingAttribute = row.otherInterestingAttribute;
callback(err, data);
}else{
callback('Row is null');
}
})
//..
}
var yourSecondSelect() = function(data, callback){
//You do your second select
//...
db.get("SELECT * from GATHER where name = " + data.name "", function(err, row) { //Note that I'm using data instead of row
if(row){
data.seconds = row.seconds;
data.otherInterestingAttribute = row.otherInterestingAttribute;
callback(err, data);
}else{
callback('Row is null');
}
})
//..
}
var decide() = function(data, callback){
if (data.somethingExists) { //Do your validations
data.type = 'update';
callback(err, data);
} else {
data.type = 'insert';
callback(err, data);
}
}
var update() = function(data,callback){
if (data.type === 'update') {
//...
//Do your stuff in order to update
seconds += row.time;//increment time
var stmt = db.prepare("UPDATE gather SET time = ? WHERE name = ?");
stmt.run([seconds, row.name], function(error){
console.log('update ' + row.idProcessed);
});
stmt.finalize();
//...
} else {
callback(err,data);
}
}
var insert() = function(data,callback){
if (data.type === 'insert') {
//...
//Do your stuff in order to insert
var stmt = db.prepare("INSTER INTO gather (name, time) VALUE(?,?)");
stmt.run([data.name, data.seconds], function(error){
console.log('lastInsert ' + this.lastID);
callback(err,data);
});
stmt.finalize();
//...
} else {
callback(err,data);
}
}
var niceWorkflow = function(){
async.waterfall([
yourFirstSelect,
yourSecondSelect,
decide,
update,
insert
],
function (err, result) {
console.log('Done');
})
}
//and call your workflow
niceWorkflow();
Off course this is not a 100% working code, I wrote it in order you look another way to do what you are trying. Many variables, validations and more are just examples and I intentionally forgot the db.each to avoid being too extense and confusing you and trying to answer your final question Is there a smarter way?.

Answer 2

You can also use Q.all from Q library.
It will return a promise after all the promises are resolved. It one promise fails, then Q.all will be rejected.