mongodb find oldest date of three keys in each document - mongodb

Question

I have a document schema that looks like this:
{
status: String,
estimateDate: Date,
lostDate: Date,
soldDate: Date,
assignedDate: Date
}
With this schema all three dates could exists and none of them could exists. I need to do a check of all three and if at least one exists use the oldest date if none exists use todays date. With the "returned" date, get the difference in days from another key (assignedDate). I have figured out how to do what I want with one date but cannot figure out how to scale this up to include all three keys. Below is the working code I have for one key.
Within my aggregate pipeline $project stage I do the following:
days: {
$cond: {
if: {
$not: ["$date1"]
},
then: {
$floor: {
$divide: [
{
$subtract: [new Date(), "$assignedDate"]
},
1000 * 60 * 60 * 24
]
}
},
else: {
$floor: {
$divide: [
{
$subtract: [
"$estimateDate",
"$assignedDate"
]
},
1000 * 60 * 60 * 24
]
}
}
}
}

Answer 1

You can use $min and $ifNull operators to get oldest date specify new Date() as default value if any of those dates does not exist:
db.col.aggregate([
{
$project: {
oldest: {
$min: [
{ $ifNull: [ "$lostDate", new Date() ] },
{ $ifNull: [ "$soldDate", new Date() ] },
{ $ifNull: [ "$assignedDate", new Date() ] },
]
}
}
}
])