Removing specific items from array with MongoDB

Question

I am developing a web app using Codeigniter and MongoDB. The users can upload files and other users can comment on them.

I store the comments in an array called comments in the main file document. This is all fine but how can I remove specific comments from the array?

I cannot use ID as key since a user can add multiple comments. How would you recommend that I can do it?

This is my comment array:

"comments": [
        {
            "user_id": ObjectId("4f240b433dc7937d68030000"),
            "user_name": "james",
            "user_comment": "This is a comment",
            "created_at": "2012-01-2821: 20: 44"
        },
        {
            "user_id": ObjectId("4f240b433dc7937d68030000"),
            "user_name": "mandy",
            "user_comment": "This is another comment",
            "created_at": "2012-01-2821: 31: 07"
        }
    ],

alecxe · Accepted Answer · 2013-06-24 11:00:41Z

60

If you can identify the comment item by matching userid, name or comment -- then you can remove that comment using update() command with $pull modifier along with the appropriate condition.

If you cannot do as above, include an unique id in the comments (like UUID).

To delete the comment, do the following:

db.coll.update({<cond to identify document}, {$pull: {'comments': {'name': <name>}}} )

If you use the id, which is preferred:

db.coll.update({<cond to identify document}, {$pull: {'comments': {'id': <id>}}} )

edited Jun 24, 2013 at 11:00

alecxe

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answered Jan 29, 2012 at 18:41

rsmoorthy

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6 Comments

Jonathan Clark Over a year ago

Sounds interesting. Can I let mongoDB assign a UUID? If yes, how?

rsmoorthy Over a year ago

Nope. For values within your document, as in this case, you need to generate UUID. PHP has uniqid(), which you can also use.

jcollum Over a year ago

Thanks for a thorough answer. The docs on this one are lackluster.

MK Yung Over a year ago

but how can I add an index for the fields in an object of an array?

mehul9595 Over a year ago

Can you show how we can do this using Linq for Mongo DB c# ?

|

Pranav Singh · Accepted Answer · 2014-02-17 05:25:45Z

4

maybe you can remove comment by its 'created_at' time, as the time is unique.

$db.coll.update({cond to identify document},{$pull:{'comments':{'created_at':<>}}})

edited Feb 17, 2014 at 5:25

Pranav Singh

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answered Feb 17, 2014 at 5:01

kevin

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1 Comment

Cees Timmerman Over a year ago

Multiple users can post in the same second, though, so i'd generate a unique id for each comment.

Phd. Burak Öztürk · Accepted Answer · 2017-08-12 22:51:10Z

0

I think, you have add mongodb id to each comment when insert it. You can create a new mongodb id like this;

$comment_id = new MongoID();

Now, you can delete comments by id with $pull + $update like @smoorthy's answer.

answered Aug 12, 2017 at 22:51

Phd. Burak Öztürk

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