Pull item by value from embedded array in Mongo

Question

I want to pull a specific item from an embedded array...assume the following mongo document....

db.test.find()

{
  id:1,
  comments : 
   [
     { cid: 1 },
     { cid: 2 },
     { cid: 3 },
     { cid: 4 },
     { cid: 5 }
   ]
}

I want to remove an item from the comments array by cid, not by position. I've tried all of these but none of them appear to work. I've tried using the dot notation, but that does not seem to have any effect. I tried the last post suggestion from How to Delete-nth element from array, but no luck...

db.test.update({ 'comments.cid' : 5}, {"$pull" :{"comments":{"cid":"3"}}}    )
db.test.update(  {id: 1}, {"$pull" : {"comments" : { "cid" : "3"}}},false,false)
db.test.update(  {id: 1}, {"$pull" :{"comments.cid" :3}})

Aleksandar Vucetic · Accepted Answer · 2012-02-05 04:36:41Z

12

this should work:

db.test.update(  {id: 1}, {$pull :{comments: {cid :3}}})

also, in your document, you have: id: 1 without comma at the end, it shold be:

id:1,

answered Feb 5, 2012 at 4:36

Aleksandar Vucetic

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5 Comments

raffian Over a year ago

This worked great, thank you...is it possible to take this one step further using findAndModify where I want to remove the array item only if the document exists, and, the array item exists? In other words, findAndModify( query:{id:1, $where "comments.cid = 3"}, ...

Aleksandar Vucetic Over a year ago

I think that with the query you already have it will remove it only if document with id 1 exists and comment with cid exists...how it would remove it anyway? :) or did I get you wrong?

raffian Over a year ago

yes, you're right, but in my document, I also have a commentsCounter, I did not mention this at first, it keeps track of the number of items in the comments array, so when I use findAndModify, I want to remove the item from the array and decrement commentsCounter only if the item exists, but if it does not, make no changes to the document at all, not the array or the counter

Aleksandar Vucetic Over a year ago

got it..not sure how that can be done though...perhaps you will have to use mongodb.org/display/DOCS/Server-side+Code+Execution for that purpose...not sure if findAndModify will help.

raffian Over a year ago

@stackoverflow.com/users/45725/vucetica I'll use you original suggestion and answer as a starting point, thanks for the help!

raffian · Accepted Answer · 2012-02-08 04:04:15Z

2

These worked too...

db.test.update({comments:{cid:4} }, 
                    {$pull:{comments:{cid:4}},  
                      $inc:{commentCount: -1}})

db.test.update({"comments.cid" : 17}, 
                     {$pull:{ comments:{cid: 17}}, 
                      $inc:{commentCount:-1}})

edited Feb 8, 2012 at 4:04

answered Feb 5, 2012 at 21:54

raffian

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1 Comment

user7364438 Over a year ago

How to pass Array of condition like

db.test.update({"comments.cid" : 17},                       {$pull:{ comments: {$in: [{cid: 17}, {cid: 18}]},                        $inc:{commentCount:-1}})

isn't working.

Amit Kumar · Accepted Answer · 2017-03-28 05:12:23Z

-2

Just wanted to modify the answer so that it can delete multiple objects from an array.

db.test.update(  {id: 1}, {"$pullAll" : {"comments" : [{ "cid" : "3"},{ "cid" : "2"}]}})

This answer has been updated and it works with mongoose too

edited Mar 28, 2017 at 5:12

answered Sep 13, 2016 at 7:55

Amit Kumar

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