async.each nested in async.waterfall - node.js

Question

I have recently started using async api. Now my requirement is to perform a join on 3 collections
namely fields, scripts and statements. fields can have multiple scripts, and scripts can have multiple statements.
here is what I have tried so far:(to join Fields collection with scripts)
// Array to hold async tasks
var asyncTasks = [];
async.waterfall([
function(callback){
// fetches fields based on some Id and it returns 2 fields
db.fields.find({entity_id: mongojs.ObjectId("54440a448bbbcbb4070131ab")}, function (err, fields) {
console.log(JSON.stringify(fields, null, 2));
callback(null, fields);
})
},
function(arg1, callback){
// arg1 now equals fields
arg1.forEach(function(eachField){
asyncTasks.push(function(callback){
db.scripts.find({fieldId: eachField._id.valueOf()}, function(err, scripts) {
// Async call is done then alert via callback
console.log(JSON.stringify(scripts, null, 2));
callback(null, scripts);
});
});
});
// Now we have an array of functions doing async tasks
// Execute all async tasks in the asyncTasks array
async.parallel(asyncTasks, function(err, results) {
// All tasks are done now
console.log("Scripts" + JSON.stringify(results, null, 2));
callback(null, "done");
});
}
], function (err, result) {
console.log(result);
});
// for the above code here is what i get the output
[
{
"_id": "54440a548bbbcbb4070131ac",
"name": "t1",
"type": "String",
"entity_id": "54440a448bbbcbb4070131ab"
},
{
"_id": "54447f1d20c103981fa1a27c",
"name": "t2",
"type": "String",
"entity_id": "54440a448bbbcbb4070131ab"
}
]
size of array 2
[]
[]
Scripts[
[],
[]
]
done
The above output doesn't print any scripts even though there are 2 scripts in database. My database is is in MongoDB, and i am using NodeJs, MongoJS api. why is db.scripts.find() returning empty array?
Any help is appreciated
I tested this piece of code to see if scripts returning the o/p. Please find below my code
test2();
function test2(){
var getScriptFunction = function(eachField, doneCallback){
if(eachField !== undefined) {
var fieldId = eachField;
console.log(fieldId);
db.scripts.find({fieldId: fieldId}, function (err, result) {
// Async call is done, alert via callback
doneCallback(null, result);
});
}
}
// The array is the id of fields
async.map(["54440a548bbbcbb4070131ac", "54447f1d20c103981fa1a27c"], getScriptFunction, function (err, results) {
// Square has been called on each of the numbers
// so we're now done!
if (err){
console.log("error!" + err);
} else {
console.log("printed from helper function \n" + JSON.stringify(results, null, 2));
}
});
}
This is the o/p of the above code to fetch scripts ran individually
printed from helper function
[
[
{
"_id": "54440a678bbbcbb4070131ad",
"name": "s1",
"fieldId": "54440a548bbbcbb4070131ac"
},
{
"_id": "544af260eb7a486824a5c306",
"name": "s2",
"fieldId": "54440a548bbbcbb4070131ac"
}
],
[]
]
This is how fields look like (db.fields.find().pretty())
[
{
"_id": "54440a548bbbcbb4070131ac",
"name": "t1",
"type": "String",
"entity_id": "54440a448bbbcbb4070131ab"
},
{
"_id": "54447f1d20c103981fa1a27c",
"name": "t2",
"type": "String",
"entity_id": "54440a448bbbcbb4070131ab"
}
]

Answer 1

I was able to solve the problem. there were 2 problems (1) I was having the same name for callback functions i.e. inner and outer callback nested within each other. (2) I had to use toString() and not valueOf()