Question

I am using redis and node (with node_redis) and I would like to serialize data from redis into an XML file (using simple-xml-writer), but I stumble upon the asynchronous behavior of node.

I have datasets for a,b,c,d and e stored as a hash in redis, the keys are data:a, data:b data:c … and each key accesses a hash. Now my XML file should look like this:

<root>
  <data record="a">
     (data for a)
  </data>
  <data record="b">
     (data for b)
  </data>
  ...
</root>

My approach is to do something like:

myobjects = Array.new();
["a","b","c","d","e"].forEach(function(str) {
   database.hmget("data:" + str,function(err,obj){ myobjects.push(obj) });
});
now_serialize_myobjects();

Is it possible to wait for the forEach-loop to finish and be sure all objects in database.hmget() are stored? So when calling the function now_serialize_myobjects(), all objects covered?

What is the best approach to that problem?

Answer 1

Simplest approach

myobjects = Array.new();
var something = ["a","b","c","d","e"]; 
something.forEach(function(str) {
   database.hmget("data:" + str,function(err,obj){ 
     myobjects.push(obj);
     if(myobjects.length === something.length){
        now_serialize_myobjects();
     }
 });
});

But why not serialize as requests return?

 startxmlfile();
 var something = ["a","b","c","d","e"]; 
 var completionCounter = 0;
 something.forEach(function(str) {
   database.hmget("data:" + str,function(err,obj){ 
     completionCounter++;
     if (!err)
        serialize(obj);
     if (completionCounter ===something.length)
        finalizexmlfile();

 });
});

if you are loading a ton of stuff second one is better I think