Mongo查询聚合Robo3T中整个集合中数组的大小

Question

Here I attached my actual document structure in my mongo collection 'Order', I need to find the count of LineValueKey(element inside array) in my entire collection (I mean, I need to aggregate the size of LineValue array in the entire collection) .In my case, say I have these 2 documents in my collection so the count of LineValueKey should return 4. For this, I m trying to figure out mongo query.

I have already tried with below query in Robo 3T 1.2.1 but I am getting below error for my actual mongo Document structure however the same query working for different mongo structure. But I need to figure out query to count the LineValueKey for my actual mongo document structure. Anyone can help on this please?

Query: db.getCollection('Order').aggregate([{$group: { _id: null, totalSize: { $sum: { $size: "$LineValue"}}} }])

Error : command failed: {
    "_t" : "OKMongoResponse",
    "ok" : 0,
    "code" : 17124,
    "errmsg" : "The argument to $size must be an array",
    "$err" : "The argument to $size must be an array"
} :

Query working Mongo Document structure:
{
    "_id" : {
        "OrderId" : 1,
        "OrderLineNumber" : 11
    },
    "OrderId" : 1,
    "OrderLineNumber" : 11,
    "vendorNbr" : 183020,
    "businessCode" : "Z",
    "itemNbr" : 552511439,
    "orderQty" : 0,    
    "LineValue" : [{
        "LineValueKey [uomCode=01]" : {
            "uomCode" : "01",
            "costAmt" : 2.78,
            "packQty" : 1,
            "retailAmt" : 3.38
        }
        },{
        "LineValueKey [uomCode=02]" : {
            "uomCode" : "02",
            "costAmt" : 2.78,
            "packQty" : 1,
            "retailAmt" : 3.38
        }
        }
    } ]
}

My case(2 documents) and Actual Document structure in Mongo Collection (Order)
{
    "_id" : {
        "OrderId" : 1,
        "OrderLineNumber" : 11
    },
    "OrderId" : 1,
    "OrderLineNumber" : 11,
    "vendorNbr" : 183020,
    "businessCode" : "Z",
    "itemNbr" : 552511439,
    "orderQty" : 0,    
    "LineValue" : {
        "LineValueKey [uomCode=01]" : {
            "uomCode" : "01",
            "costAmt" : 2.78,
            "packQty" : 1,
            "retailAmt" : 3.38
        },
        "LineValueKey [uomCode=02]" : {
            "uomCode" : "02",
            "costAmt" : 2.78,
            "packQty" : 1,
            "retailAmt" : 3.38
        }
    }
}

{
    "_id" : {
        "OrderId" : 2,
        "OrderLineNumber" : 12
    },
    "OrderId" : 2,
    "OrderLineNumber" : 12,
    "vendorNbr" : 183020,
    "businessCode" : "Z",
    "itemNbr" : 552511439,
    "orderQty" : 0,    
    "LineValue" : {
        "LineValueKey [uomCode=01]" : {
            "uomCode" : "01",
            "costAmt" : 2.78,
            "packQty" : 1,
            "retailAmt" : 3.38
        },
        "LineValueKey [uomCode=02]" : {
            "uomCode" : "02",
            "costAmt" : 2.78,
            "packQty" : 1,
            "retailAmt" : 3.38
        }
    }
}

Answer 1

As pointed before, $size needs an array to work. You have to transform your LineValue field from object to array. To performs this, use $project stage with $objectToArray operator.

db.collection.aggregate([
    {
        $project: {
          LineValue: {
            $objectToArray: "$LineValue"
          }
        }
      }
])

It will produce documents like this :

{
    "LineValue": [
      {
        "k": "LineValueKey [uomCode=01]",
        "v": {
          "costAmt": 2.78,
          "packQty": 1,
          "retailAmt": 3.38,
          "uomCode": "01"
        }
      },
      {
        "k": "LineValueKey [uomCode=02]",
        "v": {
          "costAmt": 2.78,
          "packQty": 1,
          "retailAmt": 3.38,
          "uomCode": "02"
        }
      }
    ]
  },

Then you can apply your $group stage, and count your array size. Here's the complete aggregation :

db.collection.aggregate([
  {
    $project: {
      LineValue: {
        $objectToArray: "$LineValue"
      }
    }
  },
   {
    $group: {
      _id: null,
      totalSize: {
        $sum: {
          $size: "$LineValue"
        }
      }
    }
  }
])

Will result with provided data:

[
  {
    "_id": null,
    "totalSize": 4
  }
]