Return the last “true” value for each group

Question

I have collection in which documents are like:

{
    _id: ObjectId(),
     user: ObjectId(),  
     studentName: Str         


        

Answer 1

This is a good example of need to group data by specific filed (createdAt) and then compare result set match criteria.

1. find max by student id,
2. match only entries by max entry = createdAt
3. check if they are passing criteria
4. reshape document

Code:

db.student.aggregate([{
   $group : {
       _id : "$user",
        created : {
            $max : "$createdAt"
        },
        documents : {
            $push : "$$ROOT"
        }
    }
 }, {
$project : {
    _id : 0,
    documents : {
        $filter : {
        input : "$documents",
        as : "item",
            cond : {
                $eq : ["$$item.createdAt", "$created"]
            }
        }
    }}
}, {
$match : {
    "documents.isAbandoned" : true
}},
{ $unwind : "$documents" },
{
$project : {
    _id : "$documents._id",
    user : "$documents.user",
    studentName : "$documents.studentName",
    createdAt : "$documents.createdAt",
    isAbandoned : "$documents.isAbandoned",
 }}
])