To find latest entries in array over all document, use aggregate(). Let us create a collection with documents −
> db.demo179.insertOne(
...{
... "Name":"Chris",
... "Details": [
... {
... "Id":101,
... "Subject":"MongoDB"
... },
... {
... "Id":102,
... "Subject":"MySQL"
... }
... ]
...}
...);
{
"acknowledged" : true,
"insertedId" : ObjectId("5e3980299e4f06af551997f9")
}
> db.demo179.insertOne(
...{
... "Name":"David",
... "Details": [
... {
... "Id":103,
... "Subject":"Java"
... },
... {
... "Id":104,
... "Subject":"C"
... }
... ]
...}
...);
{
"acknowledged" : true,
"insertedId" : ObjectId("5e39802a9e4f06af551997fa")
}Display all documents from a collection with the help of find() method −
> db.demo179.find().pretty();
This will produce the following output −
{
"_id" : ObjectId("5e3980299e4f06af551997f9"),
"Name" : "Chris",
"Details" : [
{
"Id" : 101,
"Subject" : "MongoDB"
},
{
"Id" : 102,
"Subject" : "MySQL"
}
]
}
{
"_id" : ObjectId("5e39802a9e4f06af551997fa"),
"Name" : "David",
"Details" : [
{
"Id" : 103,
"Subject" : "Java"
},
{
"Id" : 104,
"Subject" : "C"
}
]
}Following is the query to find latest entries in array over all documents −
> db.demo179.aggregate([
... { "$unwind": "$Details" },
... { "$sort": { "Details.Id": -1 } },
... { "$limit": 2 },
... {
... "$group": {
... "_id": "$Details.Id",
... "Name" : { "$first": "$Name" },
... "Details": { "$push": "$Details" }
... }
... },
... {
... "$project": {
... "_id": 0, "Name": 1, "Details": 1
... }
... }
...])This will produce the following output −
{ "Name" : "David", "Details" : [ { "Id" : 103, "Subject" : "Java" } ] }
{ "Name" : "David", "Details" : [ { "Id" : 104, "Subject" : "C" } ] }