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How to return the variant values of each product if that product is a variant?

I have a database in MongoDB like this

{"productId" : 1,
"isVariant": 1,
"variantId" : 1,
"attributeSet" : [ 
        {
            "name" : "Capacity",
            "value" : "500 GB",
            "id" : 3
        }, 
        {
            "name" : "Form Factor",
            "value" : "5 inch",
            "id" : 4
        }, 
        {
            "id" : 5,
            "name" : "Memory Components",
            "value" : "3D NAND"
        }
    ]
},
{"productId" : 2,
"isVariant": 1,
"variantId" : 1,
"attributeSet" : [ 
        {
            "name" : "Capacity",
            "value" : "1 TB",
            "id" : 3
        }, 
        {
            "name" : "Form Factor",
            "value" : "5 inch",
            "id" : 4
        }, 
        {
            "id" : 5,
            "name" : "Memory Components",
            "value" : "3D NAND"
        }
    ]
},
{"productId" : 3,
"isVariant": 1,
"variantId" : 1,
"attributeSet" : [ 
        {
            "name" : "Capacity",
            "value" : "500 GB",
            "id" : 3
        }, 
        {
            "name" : "Form Factor",
            "value" : "2.5 inch",
            "id" : 4
        }, 
        {
            "id" : 5,
            "name" : "Memory Components",
            "value" : "3D NAND"
        }
    ]
},
{"productId" : 4,
"isVariant": 1,
"variantId" : 1,
"attributeSet" : [ 
        {
            "name" : "Capacity",
            "value" : "1 TB",
            "id" : 3
        }, 
        {
            "name" : "Form Factor",
            "value" : "2.5 inch",
            "id" : 4
        }, 
        {
            "id" : 5,
            "name" : "Memory Components",
            "value" : "3D NAND"
        }
    ]
}

Now I want to return data where 500 GB has been in productId 1 and 3 The response should be like this:

variantValues : [{
attributeValue : "500 GB",
data : [
  {productId : 1},
  {productId : 3}
]},
{
attributeValue : "1 TB",
data : [
  {productId : 2},
  {productId : 4}
]},
{
attributeValue : "2.5 inch",
data : [
  {productId : 3},
  {productId : 4}
]},
{
attributeValue : "5 inch",
data : [
  {productId : 1},
  {productId : 2}
]}]

I have the possible values that I store in another collection for variantPossible values. The values that i am storing are like this:

"VariantValues" : {
        "3" : [ 
            "500 GB", 
            "1 TB"
        ],
        "4" : [ 
            "2.5 inch", 
            "5 inch"
        ]
    },

I want to return the variant values of each product if that product is a variant with the above format. can anyone help me with this.

Answer

You should be able to achieve this using $unwind and $group in your aggregation pipeline. This first flattens each attribute into a single document and on those you can group by the attribute value.

Finally, you can use $project to get the desired name for attributeValue:

db.collection.aggregate([
  {
    $unwind: "$attributeSet"
  },
  {
    $group: {
      _id: "$attributeSet.value",
      data: {
        "$addToSet": {
          productId: "$productId"
        }
      }
    }
  },
  {
    "$project": {
      _id: 0,
      data: 1,
      attributeValue: "$_id"
    }
  }
])

See this simplifed example on mongoplayground: https://mongoplayground.net/p/VASadZnDedc