mongodb: update array item inside of a post inside of a collection

Question

I'm trying to figure out how to update an item inside an array which is a part of a post. I did find this which looks closest to what I'm looking for: MongoDB Update Array element

But I dont have the specific post lined up first like this example seems to show. But I need to find the specific post using _id first, then update an item in the array from the resulted post.

Can I do this with one query or do I need to find the item first to then update it like the example shows in the other answer?

In the below json how could I update the first posts comments: first comment?

EDIT:

[{
    "_id": "52c06c86b78a091f26000001",
    "comments": [
        {
            "user_id": "52ad97bab142627664000001 ",
            "username": "phacer",
            "comment": "nice dress!!!",
            "created": 1390668491909,
            "_id": "_SvF-Ag4d6wFf9QR1KdAdFIpcCyI3cqm2F4rl3w7rdk="
        },
        {
            "user_id": "52ad97bab142627664000001 ",
            "username": "phacer",
            "comment": "nice dress!!!",
            "created": 1390668491909,
            "_id": "_SvF-Ag4d6wFf9QR1KdAdFIpcCyI3cqm2F4rl3w7rdk="
        }
    ],
    "desc": "Something somethingson",
    "hate": [],
    "imageurl": "some url",
    "love": [
        {
            "user_id": "52add4f4344e8ca867000001",
            "username": "asd",
            "created": 1390652212592
        }
    ],
    "tags": [
        {
            "y": 29.3,
            "brand": "Zara",
            "type": "Bow Tie",
            "x": 20,
            "color": "Black"
        }
    ],
    "user_id": "52add4f4344e8ca867000001"
},
{
    "_id": "52c06c86b78a091f26000001",
    "comments": [
        {
            "user_id": "52ad97bab142627664000001 ",
            "username": "phacer",
            "comment": "nice dress!!!",
            "created": 1390668491909,
            "_id": "_SvF-Ag4d6wFf9QR1KdAdFIpcCyI3cqm2F4rl3w7rdk="
        }
    ],
    "desc": "Something somethingson",
    "hate": [],
    "imageurl": "some url",
    "love": [
        {
            "user_id": "52add4f4344e8ca867000001",
            "username": "asd",
            "created": 1390652212592
        }
    ],
    "tags": [
        {
            "y": 29.3,
            "brand": "Zara",
            "type": "Bow Tie",
            "x": 20,
            "color": "Black"
        }
    ],
    "user_id": "52add4f4344e8ca867000001"
}]

Answer 1

您应该考虑使用$elemMatch （ 文档 ），如下所示：

.update({'_id': '52c06c86b78a091f26000001', 'comments' : {$elemMatch: {'_id': '_SvF-Ag4d6wFf9QR1KdAdFIpcCyI3cqm2F4rl3w7rdk='}}}, {$set : {'comments.$.comment': 'Lame dress!'}})

Answer 2

您可以在Mongo中使用位置运算符来访问特定的数组元素，如下所示

db.collection.update( { _id: 52c06c86b78a091f26000001 }, { $set: { "comments.$1.comment" : "dress" } } )