Redis-node library discard transactions - node.js

Question

Actually i'm using the excelent library redis-node.
But, I don't know how to make the following case to work:
I have a quantity field passed by param, then, inside a for loop, i need to use LPOP to extract the items from a first list, and RPUSH into another list, and the quantities must be the same, all inside a transaction block.
So, if the quantity param and the items extracted are different, i wan't to DISCARD the transaction, is this possible?
I put a piece of code that i've at the moment.
var redisNode = require('redis-node');
var client = redisNode.createClient();
var qty = req.params.qty;
// init transaction, lpop first and rpush finally
client.transaction(function () {
for (var i=0; i <= qty; i++) {
client.lpop(initStockListKey, function (err, item) {
if (err) throw err;
console.log('[assign] CREATE TRANSACTION list %s, pop %s', initStockListKey, item);
inProgressItems.push(item);
});
}
// pop qty validation, DISCARD
if (inProgressItems.length != qty) {
client.discard(function (err, status) {
console.log('[assign] DISCARD TRANSACTION err %s status %s', err, status);
})
}
});
I have the following error running this code:
ERR EXEC without MULTI

Answer 1

You're not using MULTI in the right way. Check the following node_redis documentation sample found in the library's GitHub repository:
var redis = require("redis"),
client = redis.createClient(), multi;
// start a separate multi command queue
multi = client.multi();
multi.incr("incr thing", redis.print);
multi.incr("incr other thing", redis.print);
// runs immediately
client.mset("incr thing", 100, "incr other thing", 1, redis.print);
// drains multi queue and runs atomically
multi.exec(function (err, replies) {
console.log(replies); // 101, 2
});
// you can re-run the same transaction if you like
multi.exec(function (err, replies) {
console.log(replies); // 102, 3
client.quit();
});
In Redis, EXEC marks the end of an atomic operation started by MULTI.