i want to generate a random number which should not be repeated based on the numbers from my mongoose db, i don't wanna use this for a unique number:
Math.floor(Math.random()*1000000000)
i found this answer which is in php here
SELECT FLOOR(RAND() * 99999) AS random_num
FROM numbers_mst
WHERE "random_num" NOT IN (SELECT my_number FROM numbers_mst)
LIMIT 1
how can i do that but in mongoose?
You could generate your random number and check that it is not already stored:
function getNumber(callback){
var n = Math.floor(Math.random()*1000000000);
YourModel.findOne({'number': n}, function(err, result){
if (err) callback(err);
else if (result) return getNumber(callback);
else callback(null, n);
});
}
getNumber(function(error, number){
console.log(number);
});
If you think this process could be called more than once in parallel, you should do some additional checks:
var alreadyRuning = false;
function getNumber(callback){
if (alreadyRuning) return setTimeout(function(){
getNumber(callback);
}, 10);
alreadyRuning = true;
var n = Math.floor(Math.random()*1000000000);
YourModel.findOne({'number': n}, function(err, result){
if (err) callback(err);
else {
alreadyRuning = false;
if (result) return getNumber(callback);
else callback(null, n);
}
});
}
getNumber(function(error, number){
console.log(number);
//...
YourModel.insert({'number': n}, function(err, result){
if (!err) alreadyRuning = false
});
});
I don't believe it is possible to do this on the database, like your SQL-example. There is a ticket for adding a $rand operator to the aggregation pipeline, but that ticket is still unresolved:
https://jira.mongodb.org/browse/SERVER-30405
Still, you could create a database-function (which can have a bad performance) and store it on the server: https://docs.mongodb.com/manual/tutorial/store-javascript-function-on-server/
That's not really a mongoose solution, though.
