How can I access the key passed to hgetall when using node_redis?

Question

I have a node.js (express) application and I'm using node_redis to get all users from my redis db.

redis = require "redis"
client = redis.createClient()

client.smembers "users", (err, user_ids) ->
  results = new Array()
  for user_id in user_ids
    client.hgetall user_id, (err, items) ->
      results.push items
      if user_ids.length is results.length
        res.json results

This produces the following result:

[
  {
    "name": "user1",
    "password": "secret"
  },
  {
    "name": "user2",
    "password": "secret"
  }
]

Now I want the user_id to be added to the user result, so I can get the following output:

[
  {
    "user:1": {
      "name": "user1",
      "password": "secret"
    }
  },
  {
    "user:2": {
      "name": "user2",
      "password": "secret"
    }
  }
]

The problem I have is that client.hgetall() is called asynchronously and I can't simply access the user_id in the for loop.

Answer 1

You need to use a closure to store user_id by introducing a function in the loop. One way to do it is to use the forEach function to iterate on the array.

Here is an example in Javascript:

var redis = require('redis')
var client = redis.createClient();

function fetch( callback ) {
   var results = new Array();
   client.smembers( "users", function(err,users) {
      if ( users.length == 0 )
         return callback( results );
      users.forEach( function(id) {
         client.hgetall(id, function(err,items) {
            var obj = {};
            obj[id] = items; # here id can be accessed since it is part of the closure
            results.push(obj);
            if ( results.length == users.length ) {
               callback( results );
            }
         });
      });
   });
}

fetch( function(results) {
   console.log(JSON.stringify(results));
});

The output is:

[ {"user:2":{"name":"user2","password":"secret2"}},
  {"user:1":{"name":"user1","password":"secret"}} ]