Get the latest record from mongodb collection

Question

This is a rehash of the previous answer but it's more likely to work on different mongodb versions.

db.collection.find().limit(1).sort({$natural:-1})

This will give you one last document for a collection

db.collectionName.findOne({}, {sort:{$natural:-1}})

$natural:-1 means order opposite of the one that records are inserted in.

Edit: For all the downvoters, above is a Mongoose syntax, mongo CLI syntax is: db.collectionName.find({}).sort({$natural:-1}).limit(1)

I need a query with constant time response

By default, the indexes in MongoDB are B-Trees. Searching a B-Tree is a O(logN) operation, so even find({_id:...}) will not provide constant time, O(1) responses.

That stated, you can also sort by the _id if you are using ObjectId for you IDs. See here for details. Of course, even that is only good to the last second.

You may to resort to "writing twice". Write once to the main collection and write again to a "last updated" collection. Without transactions this will not be perfect, but with only one item in the "last updated" collection it will always be fast.

Yet another way of getting the last item from a MongoDB Collection (don't mind about the examples):

> db.collection.find().sort({'_id':-1}).limit(1)

Normal Projection

> db.Sports.find()
{ "_id" : ObjectId("5bfb5f82dea65504b456ab12"), "Type" : "NFL", "Head" : "Patriots Won SuperBowl 2017", "Body" : "Again, the Pats won the Super Bowl." }
{ "_id" : ObjectId("5bfb6011dea65504b456ab13"), "Type" : "World Cup 2018", "Head" : "Brazil Qualified for Round of 16", "Body" : "The Brazilians are happy today, due to the qualification of the Brazilian Team for the Round of 16 for the World Cup 2018." }
{ "_id" : ObjectId("5bfb60b1dea65504b456ab14"), "Type" : "F1", "Head" : "Ferrari Lost Championship", "Body" : "By two positions, Ferrari loses the F1 Championship, leaving the Italians in tears." }

Sorted Projection ( _id: reverse order )

> db.Sports.find().sort({'_id':-1})
{ "_id" : ObjectId("5bfb60b1dea65504b456ab14"), "Type" : "F1", "Head" : "Ferrari Lost Championship", "Body" : "By two positions, Ferrari loses the F1 Championship, leaving the Italians in tears." }
{ "_id" : ObjectId("5bfb6011dea65504b456ab13"), "Type" : "World Cup 2018", "Head" : "Brazil Qualified for Round of 16", "Body" : "The Brazilians are happy today, due to the qualification of the Brazilian Team for the Round of 16 for the World Cup 2018." }
{ "_id" : ObjectId("5bfb5f82dea65504b456ab12"), "Type" : "NFL", "Head" : "Patriots Won SuperBowl 2018", "Body" : "Again, the Pats won the Super Bowl" }

sort({'_id':-1}), defines a projection in descending order of all documents, based on their _ids.

Sorted Projection ( _id: reverse order ): getting the latest (last) document from a collection.

> db.Sports.find().sort({'_id':-1}).limit(1)
{ "_id" : ObjectId("5bfb60b1dea65504b456ab14"), "Type" : "F1", "Head" : "Ferrari Lost Championship", "Body" : "By two positions, Ferrari loses the F1 Championship, leaving the Italians in tears." }

php7.1 mongoDB:
$data = $collection->findOne([],['sort' => ['_id' => -1],'projection' => ['_id' => 1]]);