Save each month, each week etc. MongoDB logic - mongodb

Question

I'm having a hard time wrapping my head around how to logically solve an issue of mine regarding data that is being read from an API and inserted into MongoDB.
Let's say I have a field called "apples", that changes in amount from month to month, due to seasonal effects, and I want to record these changes up to 6 months back, what do I do? Obviously I can't save new values for months that have passed, but looking forward, what can I do to save Novembers value for November and then Decembers value for December?
I would like to use NodeJS for this btw.
Sorry if I am unclear, it was even hard to explain!
Kind regards,
Erik

Answer 1

It sounds like you want to group things together. There is this thing called aggregation framework in mongodb.
There are a lot of things which you can do with it and one of them is grouping.
More on that you can read in $group
You can insert each apple (document) separately for the given date.
So for example:
In "2017-11-26T16:00:00Z" we have 6 apples and price 15
In "2017-11-25T16:00:00Z" we have 4 apples and price 16
In "2017-10-25T16:00:00Z" we have 9 apples and price 30
1
Lets say we have these three entries:
/* 1 */
{
"_id" : ObjectId("5a1adc774d8a2fe38bec83e4"),
"date" : ISODate("2017-11-26T16:00:00.000Z"),
"apples" : 6,
"price" : 15
}
/* 2 */
{
"_id" : ObjectId("5a1adc924d8a2fe38bec83e8"),
"date" : ISODate("2017-11-25T16:00:00.000Z"),
"apples" : 4,
"price" : 16
}
/* 3 */
{
"date" : ISODate("2017-10-25T16:00:00.000Z"),
"apples" : 9,
"price" : 30
}
Now we want to group them by month and sum the apples per month we could do the following:
db.yourCollection.aggregate([
{
$project:
{
month: { $month: "$date" },
apples: 1, // here we just assign the value of apples. There is no change here
price: 1 // also just assigning the value to price. Nothing is happening here.
}
},
{
$group: // grouping phase
{
_id: "$month", // This is what we group by
monthApples: {$sum: "$apples"} // here we sum the apples per month
monthPrice: {$sum: "$price"} // here we sum the price for each month
}
}
])
In the $project we can make use of date aggregation operators.
The above aggregation pipeline would result to this:
/* 1 */
{
"_id" : 10, // month (October)
"monthApples" : 9 // sum of apples
"monthPrice" : 30 // sum of price for month 10
}
/* 2 */
{
"_id" : 11, // month (November)
"monthApples" : 10 // sum of apples
"monthPrice" : 31 // sum of price for month 11
}
2
Now imagine we have the apple type also saved in the database.
/* 1 */
{
"_id" : ObjectId("5a1adc774d8a2fe38bec83e4"),
"date" : ISODate("2017-11-26T16:00:00.000Z"),
"apples" : 6,
"price" : 15,
"appleType" : "Goldrush"
}
/* 2 */
{
"_id" : ObjectId("5a1adc924d8a2fe38bec83e8"),
"date" : ISODate("2017-11-25T16:00:00.000Z"),
"apples" : 4,
"price" : 16,
"appleType" : "Pink Lady"
}
/* 3 */
{
"_id" : ObjectId("5a1b1c144d8a2fe38bec8a56"),
"date" : ISODate("2017-10-25T16:00:00.000Z"),
"apples" : 9,
"price" : 30,
"appleType" : "Pink Lady"
}
We could group for example by apple type like that.
db.yourCollection.aggregate([
{
$project:
{
apples: 1, // here we just assign the value of apples. There is no change here
price: 1, // also just assigning the value to price. Nothing is happening here.
appleType: 1
}
},
{
$group: // grouping phase
{
_id: "$appleType", // group by appletype
monthApples: {$sum: "$apples"}, // here we sum the apples per month
monthPrice: {$sum: "$price"} // here we sum the price for each month
}
}
])

Answer 2

One of the possible way to model this data will be creating a document for each product that will store it's pricing history for a month:
{
product: "apple",
amount:[
{day: ISODate("2017-11-01T00:00:00.000Z"), price: 24},
{day: ISODate("2017-11-02T00:00:00.000Z"), price: 20},
{day: ISODate("2017-11-03T00:00:00.000Z"), price: 19},
{day: ISODate("2017-11-03T00:00:00.000Z"), price: 25}
],
quality: "best"
}