MongoDB $limit inside an $and - mongodb

Question

I'm looking to implement a query that will return me a single JSON with 2 sets of data together.
What I look for is to retrieve 40 orders which offerDate is still in the future ( $gte: today ) and 8 orders which offerDate is in the past.
Currently I only have the 40 in the future like so:
const orders = await db.Order.aggregate([
{
$match: {
offerDate: {
$gte: moment().startOf('day').toDate(),
},
},
},
{
$limit: 40,
},
How could I achieve to add the limit inside an $and to get both together?
I tried with:
$match: {
$and: [
{
offerDate: {
$gte: moment().startOf('day').toDate(),
},
$limit: 40
},
{
offerDate: {
$lte: moment().startOf('day').toDate(),
},
$limit: 8
},
]
}
},
But that didn't work at all and I cannot find the right way to do it.
Thanks a lot!

Answer 1

$limit is a pipeline stage which cannot be used within any other stage so what you're trying is not the way to go. You simply need two separate $matches followed by $limit and the $facet operator allows you to do that:
{
$facet: {
greater: [
{ $match: { offerDate: { $gte: moment().startOf('day').toDate() } } },
{ $limit: 40 }
],
lower: [
{ $match: { offerDate: { $lte: moment().startOf('day').toDate() } } },
{ $limit: 8 }
]
}
},
{
$project: {
all: { $concatArrays: [ "$greater", "$lower" ] }
}
}