Spring data mongodb hierarchy

Question

I have a nested json object in a hierarchical structure as defined below

[
    {
        "categoryId": 1,
        "categoryName": "Category 1",
        "childCategory": null,
        "active": false
    },
    {
        "categoryId": 2,
        "categoryName": "Category 2",
        "active": true,
        "childCategory": [
            {
                "categoryId": 4,
                "categoryName": "Category 4",
                "childCategory": null,
                "active": false
            },
            {
                "categoryId": 5,
                "categoryName": "Category 5",
                "childCategory": null,
                "active": true
            }
        ]
    },
    {
        "categoryId": 10,
        "categoryName": "Category 10",
        "childCategory": null,
        "active": true
    }
]

From this I want to select all the active categories to a single array structure. My output should be

[
    {
        "categoryId": 2,
        "categoryName": "Category 2",
        "active": true
    },
    {
        "categoryId": 5,
        "categoryName": "Category 5",
        "active": true
    },
    {
        "categoryId": 10,
        "categoryName": "Category 10",
        "active": true
    }
]

Is it possible to directly fetch this data in a single query statement. I am using spring data for mongodb.

s7vr · Accepted Answer · 2017-02-10 22:35:49Z

1

You can try below aggregation.

$redact to go through a document level at a time and perform $$DESCEND and $$PRUNE on the matching criteria.

$unwind the $childCategory with preserveNullAndEmptyArrays to keep the array with null values.

db.collection.aggregate({
    $redact: {
        $cond: [{
            $eq: ["$active", true]
        }, "$$DESCEND", "$$PRUNE"]
    }
}, {
    $unwind: {
        path: "$childCategory",
        preserveNullAndEmptyArrays: true
    }
})

answered Feb 10, 2017 at 22:35

s7vr

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