MongoDB GroupBy to set status

To group documents by status and categorize them into different arrays in MongoDB, use the aggregate() method with $group, $cond, and $push operators to conditionally separate documents based on their status values.

Syntax

db.collection.aggregate([
    {
        $group: {
            _id: null,
            "categoryName": {
                $push: {
                    $cond: [
                        { $eq: ["$fieldName", value] },
                        { _id: "$_id", fieldName: "$fieldName" },
                        false
                    ]
                }
            }
        }
    },
    {
        $project: {
            _id: 0,
            "categoryName": {
                $setDifference: ["$categoryName", [false]]
            }
        }
    }
]);

Sample Data

db.demo149.insertMany([
    { "Status": 40 },
    { "Status": 40 },
    { "Status": 50 }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e350386fdf09dd6d08539c4"),
        ObjectId("5e350388fdf09dd6d08539c5"),
        ObjectId("5e35038afdf09dd6d08539c6")
    ]
}

Display all documents from the collection ?

db.demo149.find();

{ "_id": ObjectId("5e350386fdf09dd6d08539c4"), "Status": 40 }
{ "_id": ObjectId("5e350388fdf09dd6d08539c5"), "Status": 40 }
{ "_id": ObjectId("5e35038afdf09dd6d08539c6"), "Status": 50 }

Example: Group by Status and Set Categories

Group documents by status values and categorize them into "done" (Status=40) and "notdone" (Status=50) arrays ?

db.demo149.aggregate([
    {
        "$group": {
            "_id": null,
            "done": {
                "$push": {
                    "$cond": [
                        { "$eq": ["$Status", 40] },
                        { "_id": "$_id", "Status": "$Status" },
                        false
                    ]
                }
            },
            "notdone": {
                "$push": {
                    "$cond": [
                        { "$eq": ["$Status", 50] },
                        { "_id": "$_id", "Status": "$Status" },
                        false
                    ]
                }
            }
        }
    },
    {
        "$project": {
            "_id": 0,
            "done": {
                "$setDifference": ["$done", [false]]
            },
            "notdone": {
                "$setDifference": ["$notdone", [false]]
            }
        }
    }
]);

{
    "done": [
        { "_id": ObjectId("5e350386fdf09dd6d08539c4"), "Status": 40 },
        { "_id": ObjectId("5e350388fdf09dd6d08539c5"), "Status": 40 }
    ],
    "notdone": [
        { "_id": ObjectId("5e35038afdf09dd6d08539c6"), "Status": 50 }
    ]
}

How It Works

• $group with _id: null groups all documents into a single group
• $cond conditionally pushes documents into arrays based on status values
• $setDifference removes false values from arrays, keeping only matched documents
• $project shapes the final output and excludes the _id field

Conclusion

Use MongoDB's aggregation pipeline with $group, $cond, and $setDifference operators to group documents by status values and organize them into categorized arrays. This approach provides flexible document categorization based on field conditions.