Removing specific items from array with MongoDB

问题:

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"
        }
    ],

回答1:

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>}}} )

回答2:

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':<>}}})

回答3:

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.