MongoDB dateDiff between multiple documents - mongodb

Question

I have collection in my mongoDB which stores service given to customer along with their email address something like below
{
"_id" : ObjectId("56a84627f8fd4a136c0e944a"),
"Vehicle" : "Honda",
"ServiceSelected" : "FULL SERVICE",
"FullName" : "xyz",
"Email" : "xyz#xyz.com",
"BookingTime" : ISODate("2015-12-27T06:00:00.000Z")
},
{
"_id" : ObjectId("56a84627f8fd4a136c0e944b"),
"Vehicle" : "AUDI",
"ServiceSelected" : "FLAT TYRE",
"FullName" : "abc",
"Email" : "abc#abc.com",
"BookingTime" : ISODate("2015-12-26T06:00:00.000Z")
},
{
"_id" : ObjectId("56a84627f8fd4a136c0e944c"),
"Vehicle" : "BMW",
"ServiceSelected" : "OTHERS",
"FullName" : "def",
"Email" : "def#def.com",
"BookingTime" : ISODate("2015-12-25T06:00:00.000Z")
},
{
"_id" : ObjectId("56a84627f8fd4a136c0e944d"),
"Vehicle" : "BMW",
"ServiceSelected" : "OTHERS",
"FullName" : "def",
"Email" : "def#def.com",
"BookingTime" : ISODate("2015-12-30T06:00:00.000Z")
},
{
"_id" : ObjectId("56a84627f8fd4a136c0e944a"),
"Vehicle" : "Honda",
"ServiceSelected" : "FULL SERVICE",
"FullName" : "xyz",
"Email" : "xyz#xyz.com",
"BookingTime" : ISODate("2016-01-27T06:00:00.000Z")
}
From the above collection I want to fetch all the documents that have taken our service with a gap of at-least 30 days i.e. from the above collection "Email" : "xyz#xyz.com" should be returned but not "Email" : "def#def.com" as the second service was taken with in 5 days.
I know there is flaw in the design and an additional flag can be set while inserting the record from the application but I need to fetch the data for the existing records.

Answer 1

You need to use the $min and $max operators which respectively return the minimum and maximum value for "BookingTime" in your $group stage. The last stage in the pipeline is the $redact stage where you use a simple "date" math using the $divide and $subtract arithmetic operators.to return those documents where the number of days between first "service" and last "service" is greater than 30
db.collection.aggregate( [
{ "$group": {
"_id": "$Email",
"date1": { "$min": "$BookingTime" },
"date2": { "$max": "$BookingTime" }
}},
{ "$redact": {
"$cond": [
{ "$gte": [
{ "$divide": [
{ "$subtract": [ "$date2", "$date1" ] },
1000 * 60 * 60 * 24
]},
30
]},
"$$KEEP",
"$$PRUNE"
]
}}
])
Which returns:
{
"_id" : "xyz#xyz.com",
"date1" : ISODate("2015-12-27T06:00:00Z"),
"date2" : ISODate("2016-01-27T06:00:00Z")
}
Another way to do this is by using the $cond operator in a $project stage to avoid a collection scan.
db.collection.aggregate( [
{ "$group": {
"_id": "$Email",
"date1": { "$min": "$BookingTime" },
"date2": { "$max": "$BookingTime" },
"count": { "$sum": 1 }
}},
{ "$match": { "count": { "$gte": 2 } } },
{ "$project": {
"emails": {
"$cond": [
{ "$gte": [
{ "$divide": [
{ "$subtract": [ "$date2", "$date1" ] },
1000 * 60 * 60 * 24
]},
30
] },
"$_id",
false
]
}
}},
{ "$match": { "emails": { "$ne": false } } }
])

Answer 2

You can get first sales date and last sales date by $min and $max:
db.services.aggregate({
$group: {
"_id" :"$Email",
lastSalesDate: { $max: "$BookingTime" },
firstSalesDate: { $min: "$BookingTime" }
}
}
)
After that you can add filter based on lastSalesDate. You can calculate ISO date which 30 days before. ex. ISODate("2015-12-28T00:00:00.000Z"). By $lt , you will get customers of 30 days before.
db.services.aggregate(
{
$group: {
"_id" :"$Email",
lastSalesDate: { $max: "$BookingTime" },
firstSalesDate: { $min: "$BookingTime" }
}
},
{
$match : {
"lastSalesDate" : { $lt: ISODate("2015-12-28T00:00:00.000Z") }
}
}
)
Results like:
{
"_id" : "abc#abc.com",
"lastSalesDate" : ISODate("2015-12-26T06:00:00.000+0000"),
"firstSalesDate" : ISODate("2015-12-26T06:00:00.000+0000")
}

Answer 3

This is what I used finally
db.services.aggregate(
{$group: {
"_id" :"$Email",
count:{$sum:1},
lastSalesDate: { $max: "$BookingTime" },
firstSalesDate: { $min: "$BookingTime" }
},
{$project:{
_id:1,count:1,dateDifference: { $divide:[ {$subtract: [ "$lastSalesDate", "$firstSalesDate" ]},86400000] }
}
},
{$match:{
count:{$gt:1},dateDifference:{$gt:20}
}
}
}
)
Count > 1 helped to filter the records which never repeated and datedifferentce > 20 is for days as I already converted milliseconds to days using division operation.