I have the following aggregation that is supported by MongoDB 5 but not 4.4. How can I write this in v4.4?
Aggregation Pipeline (V5):
"$ifNull": [
{
"$getField": {
"field": "prices",
"input": {
"$first": "$matchedUsers"
}
}
},
[]
]
Here's a MongoDB Playground for the same.
This pipeline should work in version 4.4:
db.datasets.aggregate([
{
"$lookup": {
"from": "users",
"localField": "assignedTo",
"foreignField": "id",
"as": "matchedUsers"
}
},
{
"$addFields": {
"cgData": {
"$first": "$matchedUsers"
}
}
},
{
"$addFields": {
"cgData": {
"$first": {
"$filter": {
"input": {
"$ifNull": [
"$cgData.prices",
[]
]
},
"as": "currentPrice",
"cond": {
"$and": [
{
"$gte": [
"$firstBillable",
"$$currentPrice.beginDate"
]
},
{
$or: [
{
$eq: [
{
$type: "$$currentPrice.endDate"
},
"missing"
]
},
{
"$lt": [
"$firstBillable",
"$$currentPrice.endDate"
]
}
]
}
]
}
}
}
}
}
},
{
"$addFields": {
cgPrice: "$cgData.price"
}
},
{
"$project": {
cgData: 0,
"matchedUsers": 0
}
}
])
In this, a new $addFields stage is added, to get first element of matchedUsers array.
{
"$addFields": {
"cgData": {
"$first": "$matchedUsers"
}
}
}
Then we use $ifNull like this:
{
"$ifNull": [
"$cgData.prices",
[]
]
}
See it working here.