Fill missing dates in records

Question

I have a collection of ProductViews.

ProductView

{
    productId: \'5b8c0f3204a10228b00a1745,
    createdAt: \'2018-09-         


        

Answer 1

I would suggest you add the missing date client side if it's only one or two and the number of document to process is small.

That being said, the following pipeline only works on MongoDB 4.0+ but with a little effort, we can make it work in 3.6.

[
    {
        $group: {
            _id: null,
            dates: {
                $push: {
                    $let: {
                        vars: {
                            date: {
                                $dateToParts: {
                                    date: {
                                        $toDate: "$createdAt"
                                    }
                                }
                            }
                        },
                        in: {
                            $toDouble: {
                                $dateFromParts: {
                                    year: "$$date.year",
                                    month: "$$date.month",
                                    day: "$$date.day"
                                }
                            }
                        }
                    }
                }
            }
        }
    },
    {
        $addFields: {
            startDate: {
                $divide: [
                    {
                        $min: "$dates"
                    },
                    1000
                ]
            },
            endDate: {
                $divide: [
                    {
                        "$max": "$dates"
                    },
                    1000
                ]
            }
        }
    },
    {
        $addFields: {
            dates: {
                $map: {
                    input: {
                        $concatArrays: [
                            "$dates",
                            {
                                $setDifference: [
                                    {
                                        $map: {
                                            input: {
                                                $range: [
                                                    {
                                                        $toDouble: "$startDate"
                                                    },
                                                    {
                                                        $toDouble: "$endDate"
                                                    },
                                                    24*60*60
                                                ]
                                            },
                                            in: {
                                                $multiply: [
                                                    "$$this",
                                                    1000
                                                ]
                                            }
                                        }
                                    },
                                    "$dates"
                                ]
                            }
                        ]
                    },
                    in: {
                        $toDate: "$$this"
                    }
                }
            }
        }
    },
    {
        "$unwind": "$dates"
    },
    {
        "$group": {
            _id: "$dates",
            views: {
                $sum: 1
            }
        }
    },
    {
        "$sort": {
            _id: -1
        }
    }
]