Mongodb update subdocument inside array field of a collection - mongodb

Question

I have a mongodb collection like
{
"_id" : ObjectId("5375ef2153bb790b20d8a660"),
"association" : [
{
"count" : 3,
"name" : "hayatdediğin"
},
{
"count" : 2,
"name" : "sadecesenolsan"
},
{
"count" : 2,
"name" : "üslupnamustur"
}
],
"tag_count" : 4,
"tag_name" : "vazgeçilmezolan",
"variation" : [
{
"count" : 4,
"name" : "VazgeçilmezOlan"
}
]
}
Each collection consists of tag_name, tag_count, array field association and array field variation. For each name inside association, there exists a different document same as this document. I need to add new field "total_count" inside each association dictionary whose value equals the tag_count of the name by querying the database.
I tried this code but its not working
db.hashtag.find().forEach(function (doc) {
if (doc.association.length != 0 ) {
doc.association.forEach(function (assoc) {
db.hashtag.find({'tag_name': assoc.name}).forEach(function(tag){
assoc.total_count=tag.tag_count;
})
});
}
});

Answer 1

After modifying each doc you need to call save on the collection to commit the change.
Assuming you're doing this in the shell:
db.hashtag.find().forEach(function (doc) {
if (doc.association.length != 0 ) {
doc.association.forEach(function (assoc) {
db.hashtag.find({'tag_name': assoc.name}).forEach(function(tag){
assoc.total_count=tag.tag_count;
});
});
// Save the changed doc back to the collection
db.hashtag.save(doc);
}
});

Answer 2

To update doc in database you have to use db.hashtag.update, not db.hashtag.find. Find only retrieves document from db.

Answer 3

I changed the previous method of looping using forEach and then saved the doc at last and the code worked.
db.hashtag.find().forEach(function (doc) {
var array = doc.association;
if (array != undefined){
for(var i=0;i<array.length;i++)
{
var obj = db.hashtag.findOne({'name':array[i].name});
var count = obj.count;
doc.association[i].total_count = count;
db.hashtag.save(doc);
}
}
});