mongodb - how to find and then aggregate

Question

I have collection that contains documents with below schema. I want to filter/find all documents that contain the gender female and aggregate the sum of brainscore. I tried the

Answer 1

Here is an answer if the DOB numbers needs to be converted to Date then compared. If not, a number or Date such as 1970 will be incorrectly $gte to 19400801 (you can try):

db['!all'].aggregate([
    {
        $addFields: {
            "_temp_DOB": {
                $dateFromString: {
                    dateString: {$toString: {$toLong: "$DOB"}},
                    format: "%Y%m%d"
                }
            }
        }   
    },
    {
        $match: {
            'GENDER': 'F', 
            '_temp_DOB': { $gte: new Date("1940-08-01"),  
                           $lte: new Date("2013-12-31") }
        }
    },
    {
        $group: {
            _id: "$GENDER", 
            totalscore: { $sum: "$BRAINSCORE" }
        }
    }
])

Outputs:

{ "_id" : "F", "totalscore" : 109 }