MongoDB get remaining seats of restaurant - node.js

Question

I've problem to find remaining seats of particular restaurant in a particular Date range
Let me define my problem. Suppose I've a collection it called booking
In this have a following fields:
Booking ID
User ID
Restaurant ID
Booking Start Date (date saved in Timestamp)
Booking End Date (date saved in Timestamp)
Booked Seat
If there are 50 seats in restaurant. And I want to check available seats of a particular date range for example the date range is 6-12(This range in timestamp)"(Start Date) - (End Date)"
How to calculate the total remaining seats of restaurant.
If anyone have any idea please let me know.
Thanks in advance
Code is here
const where = {};
where.restaurant_id = 126;
where.user_id = 1;
where.start_date = { $gte: 6 };
where.end_date = { $gte: 12 };
const remainingSeats = getSeatsAvailability(where);
function getSeatsAvailability(where) {
return new Promise((resolve, reject) => {
bookingModel.find(where, (err, details) => {
if (err) { reject(err); } else { resolve(details); }
});
});
}

Answer 1

So, What I have Visualized is the below diagram, so there are basically four cases to be covered:
x y
a-----------|---------b |
a-|------------|---b
| a-------b |
| a-----|--------b
So the formulae are:
1. a<x, a<y | b>x, b<y
2. a<x, a<y | b>x, b>y
3. a>x, a<y | b>x, b>y
4. a>x, a<y | b<y, b>x
I am pasting an ROUGH example, take it as a hint to solve the problem at hand:
db.collection.aggregate([
{
$match: {
$or: [
{
a: {
$lte: 3,
$lte: 9
},
$or: [
{
b: {
$gte: 3,
$lte: 9
}
},
{
b: {
$gte: 3,
$gte: 9
}
}
]
},
{
a: {
$gte: 3,
$lte: 9
},
$or: [
{
b: {
$gte: 3,
$gte: 9
}
},
{
b: {
$gte: 3,
$lte: 9
}
}
]
}
],
r: 1
}
},
{
$group: {
_id: null,
sum_booked: {
$sum: "$c"
}
}
},
{
$project: {
seats_left: {
$subtract: [
50,
"$sum_booked"
]
}
}
}
])
The example dataset that I have tested on:
[
{
a: 1,
b: 10,
c: 10,
r: 1,
},
{
a: 2,
b: 5,
c: 15,
r: 1
},
{
a: 5,
b: 10,
c: 10,
r: 1
},
{
a: 7,
b: 15,
c: 15,
r: 12 <<<<========/////DIFF REST ID
}
]
Output:
[
{
"_id": null,
"seats_left": 15
}
]

Answer 2

db.booking.aggregate([{
$match: {
BookingStartDate: { $lte: date_range_end },
BookingEndDate: { $gte: date_range_start },
RestaurantID: restaurant_id
}
},
{
$group: {
_id: '$RestaurantID',
TotalBookedSeat: { $sum: '$BookedSeat' }
}
},
{
$project: {
LeftSeat: { $subtract: [50, '$TotalBookedSeat'] },
_id: 0
}
}
])
{ "_id" : ObjectId("5d8479f6902a52448029a6d0"), "bid" : 1, "uid" : 1, "rid" : 126, "bsd" : 1, "bed" : 10, "bs" : 10 }
{ "_id" : ObjectId("5d847a11902a52448029a6d1"), "bid" : 2, "uid" : 1, "rid" : 126, "bsd" : 2, "bed" : 5, "bs" : 15 }
{ "_id" : ObjectId("5d847a24902a52448029a6d2"), "bid" : 3, "uid" : 1, "rid" : 126, "bsd" : 5, "bed" : 10, "bs" : 10 }
{ "_id" : ObjectId("5d847a34902a52448029a6d3"), "bid" : 4, "uid" : 1, "rid" : 126, "bsd" : 7, "bed" : 15, "bs" : 15 }
db.booking.aggregate([{ $match: { bsd: { $lte: 12 }, bed: { $gte: 6 }, rid: 126 } }, { $group: { _id: '$rid', total_seat_sold: { $sum: '$bs' } } }])
The result of the above is 35, then 15 seats left.
This time it will works I think.