1

After a few pipeline stages, I came up with following sample result which is one document. If the videos.views.userId contains 10, I need to indicate videos.isWatched = true else false. We can use $unwind, check the condition, then group it.

This is sample output, The original document contains a lot of field, so I just like to do with less code unless I need to unwind Is there any way to do without unwind("videos")?

[
    {
        "_id":"someId",
        "videos":[
            {
                "_id":"1",
                "name":"A",
                "views":[
                    {
                        "userId":10,
                        "group":"X"
                    }
                ]
            },
            {
                "_id":"2",
                "name":"B",
                "views":[
                    {
                        "userId":20,
                        "group":"Y"
                    }
                ]
            }
        ],
        "Assessment":[
            {
                "_id":"22",
                "title": "Hello world"
            }
        ]
    }
]

Expected result

[
    {
        "_id":"someId",
        "videos":[
            {
                _id:"1",
                name:"A",
                views:[
                    {
                        userId:10,
                        group:"X"
                    }
                ],
                "isWatched":true
            },
            {
                _id:"2",
                name:"B",
                views:[
                    {
                        userId:20,
                        group:"Y"
                    }
                ],
                "isWatched":false
            }
        ],
        "Assessment":[
            {
                _id:"22",
                title: "Hello world"
            }
        ]
    }
]
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1 Answer 1

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1

You can use $map along with $mergeObjects to add a new field to an existing array. $anyElementTrue can be used to determine whether there's any userId equal to 10:

db.collection.aggregate([
    {
        $addFields: {
            videos: {
                $map: {
                    input: "$videos",
                    in: {
                        $mergeObjects: [
                            "$$this",
                            { 
                                isWatched: {
                                    $anyElementTrue: {
                                        $map: { input: "$$this.views", in: { $eq: [ "$$this.userId", 10 ] } }
                                    }
                                }  
                            }
                        ]
                    }
                }
            }
        }
    }
])

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