*******Aggregate take agurement of array //
let printing every thing 1
db.payment.aggregate();
//// joning collection payment on collection users on id of payment id of users 2
db.payment.aggregate([ { $lookup: { from: "users", localField: "id", foreignField: "id" ,as: "user" } } ])
///unwind to romove from array and project state fields when to display 3
db.payment.aggregate([ { $lookup: { from: "users", localField: "id", foreignField: "id" ,as: "user" } } ,{"$unwind":"$user"},{$project:{"id":"$id","amount":"$amount","name":"$user.name" }} ])
////group: display unique value base on the key specified 4
db.payment.aggregate([ { $lookup: { from: "users", localField: "id", foreignField: "id" ,as: "user" } } ,{"$unwind":"$user"},{$project:{"id":"$id","amount":"$amount","name":"$user.name" }}, {$group: { _id: {"id" : "$id" }} }])
////display other fieds from the group .. f 5
operators include
$sum : sum the specifield constant or field
$first: display the first value
$last: display the last value
db.payment.aggregate([ { $lookup: { from: "users", localField: "id", foreignField: "id" ,as: "user" } } ,{"$unwind":"$user"},{$project:{"id":"$id","amount":"$amount","name":"$user.name" }}, {$group: { _id: {"id" : "$id" }, "sumi":{"$sum": "$amount"}, "name":{"$first": "$name"} ,"id":{"$first": "$id"} } } ])
project result from the last operation 6
db.payment.aggregate([ { $lookup: { from: "users", localField: "id", foreignField: "id" ,as: "user" } } , {"$unwind":"$user"} , {$project:{"id":"$id","amount":"$amount","name":"$user.name" }}, {$group: { _id: {"id" : "$id" },"sumi":{"$sum": "$amount"},"name":{"$first": "$name"} ,"id":{"$first": "$id"} } }, {$match:{"sumi":{$gt:2500}}}, {$project:{"_id":"0","id":"$id","name":"$name" ,"amount":"$sumi" }}])
//////////////////////////////////////////////////////////////////////////////////////////////////////JAVA CODE https://youtu.be/ps-jZM05mWE /////////////////////////////////////////////////////////////////////////////////////////////////////////////
MongoCollection<Document> collection = database.getCollection("payment");
collection.aggregate(Arrays.asList(
///lookup stage
Aggregates.lookup("users", "id","id" , "user")
//group stage ,Aggregates.group("$id",Accumulators.sum("commulativeSum", "$amount"),Accumulators.first("name", "$user.name"))
// match stage ,Aggregates.match(Filters.gt("commulativeSum", 2500))
//projection stage ,Aggregates.project(Projections.fields(Projections.include("commulativeSum","name") ) )
));
