Spring data mongodb hierarchy - mongodb

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.

Answer 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
}
})