Fetch mongo documents based on date - mongodb

Question

We are inserting mongo documents with identifier and there is a subarray within the documents.
insert 1 :
db.test.insert(
{
"companyId" : "123",
"persons" : [
{
"joiningDate" : NumberLong("1431674741623"),
"name" : "Rajesh"
}
],
})
insert 2 :
db.test.insert(
{
"companyId" : "123",
"persons" : [
{
"joiningDate" : NumberLong("1431674741653"),
"name" : "Rahul"
}
],
})
I would like to retreive the company details based on the company id and merge the persons into one array list, and sort the persons based on the joining date.
Currently I am able to retreive the data using QueryBuilder but I am unable to sort the person based on the date.I can use java comparator to do the same , but I am looking out if there is any API from mongo db java driver which can be used to get the same.
Thanks.

Answer 1

you should use mongo aggregation like first $unwind persons array and then sort persons.joiningDate and then group with push as below :
db.test.aggregate({
"$match": {
"companyId": "123" // match companyId
}
}, {
"$unwind": "$persons" //unwind person array
}, {
"$sort": {
"persons.joiningDate": -1 //sort joining date
}
}, {
"$group": {
"_id": "$companyId",
"persons": {
"$push": "$persons" //push all sorted data into persons
}
}
}).pretty()
For converting this code into java use mongo java aggregation as
// unwind persons
DBObject unwind = new BasicDBObject("$unwind", "$persons");
// create pipeline operations, with the $match companyId
DBObject match = new BasicDBObject("$match", new BasicDBObject("companyId", "123"));
// sort persons by joining date
DBObject sortDates = new BasicDBObject("$sort", new BasicDBObject("persons.joiningDate", -1)); // -1 and 1 descending or ascending resp.
// Now the $group operation
DBObject groupFields = new BasicDBObject("_id", "$companyId");
groupFields.put("persons", new BasicDBObject("$push", "$persons"));
DBObject group = new BasicDBObject("$group", groupFields);
// run aggregation
List < DBObject > pipeline = Arrays.asList(match, unwind,sortDates, group);
AggregationOutput output = test.aggregate(pipeline);
for(DBObject result: output.results()) {
System.out.println(result);
}