CODEWITHSUNDEEP
mongodbmongodb-queryaggregation-framework
Boat
Boat

Reputation: 535

Mongo aggregation to collect array elements based on field name

I have an aggregated mongo document like below. There are two different batches ("-Minor" and "-Major"), and each batch has "batchElements" too. 

{
    "_id" : "123",
    "info" : {
        "batch" : "Batch1-Minor"
    },
    "batchElements" : {
        "elements" : [ 
             { },  { }, .... { }
        ]
    }
},
{
    "_id" : "123",
    "info" : {
        "batch" : "Batch2-Minor"
    },
    "batchElements" : {
        "elements" : [ 
             { },  { }, .... { }
        ]
    }
},
{
    "_id" : "123",
    "info" : {
        "batch" : "Batch3-Major"
    },
    "batchElements" : {
        "elements" : [ 
             { },  { }, .... { }
        ]
    }
},
{
    "_id" : "123",
    "info" : {
        "batch" : "Batch4-Major"
    },
    "batchElements" : {
        "elements" : [ 
             { },  { }, .... { }
        ]
    }
}

How can I collect all "batchElements" of "-Minor" and "-Major" and create a document as below;

Output:

  {
    "_id" : "123",
    "minorElements" : [
        [{}, {}, {}, ..... {} ], // elements of "Batch1-Minor"
        [{}, {}, {}, ..... {} ], // elements of "Batch2-Minor"
        ...                      // elements of "BatchN-Minor"
    ],
    "majorElements" : [
        [{}, {}, {}, ..... {} ], // elements of "Batch3-Major"
        [{}, {}, {}, ..... {} ], // elements of "Batch4-Major"
        ...                      // elements of "BatchN-Major"
    ]
}

Upvotes: 3

Views: 769

Answers (1)

mickl
mickl

Reputation: 49945

You can start with $split to get the "type" of your batch as part of your $group _id. Then you can run another $group to make minor and major parts of the same document. In the last step you need $replaceRoot along with $arrayToObject to promote both arrays into root level.

db.collection.aggregate([
    {
        $group: {
            _id: {
                id: "$_id",
                type: { $arrayElemAt: [ { $split: [ { $toLower: "$info.batch" }, "-" ] }, 1 ] }
            },
            docs: { $push: "$batchElements.elements" }
        }
    },
    {
        $group: {
            _id: "$_id.id",
            data: { $push: { k: { $concat: ["$_id.type","Elements"] }, v: "$docs" } }
        }
    },
    {
        $replaceRoot: {
            newRoot: {
                $mergeObjects: [ { _id: "$_id" }, { $arrayToObject: "$data" } ]
            }
        }
    }
])

Mongo Playground

Upvotes: 2

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