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How to return only 1 field in MongoDB?

I'm trying to get the order number where a transactionId is equal to another variable I have in my code. My tolls.booths collection looks like this
In my code,
def boothsException = booths.find([ "pings.loc.transactionId": tollEvent.id, "pings.loc.order":1] as BasicDBObject).iterator()
println boothsException
I am getting boothsException = DBCursor{collection=DBCollection{database=DB{name='tolls'}
I would like to essentially say get where transactionId = 410527376 and give me that order number in boothsException (5233423).

This is using MongoDB Java Driver v3.12.2.
The code extracts the value from the returned cursor. I am using newer APIs, so you will find some differences in class names.
int transId = 410527376; // same as tollEvent.id
MongoCursor<Document> cursor = collection
.find(eq("pings.loc.transactionId", transId))
.projection(fields(elemMatch("pings.loc.transactionId"), excludeId()))
.iterator();
while (cursor.hasNext()) {
Document doc = cursor.next();
List<Document> pings = doc.get("pings", List.class);
Integer order = pings.get(0).getEmbedded(Arrays.asList("loc","order"), Double.class).intValue();
System.out.println(order.toString()); // prints 5233423
}
NOTES:
The query with projection gets the following one sub-document from the pings array:
"pings" : [
{
"upvote" : 575,
"loc" : {
"type" : "2dsphere",
"coordinates" : [ .... ],
"transactionId" : 410527376,
"order" : 5233423
},
...
}
]
The remaining code with looping the cursor is to extract the order value from it.
The following are the imports used with the find method's filter and projection:
import static com.mongodb.client.model.Filters.*;
import static com.mongodb.client.model.Projections.*;

How to delete mongodb document with two conditions one with $gt operator?

I would like to retrieve the following information:
delete from database where name = 'AAA' and age>20;
but for MongoDB in Java. Essentially, it should delete the document that contain the word AAA and age greater than 20 in them. I know that there is the $in operator in MongoDB, but how do I do the same in Java, using the Java driver? I've been trying to look for it everywhere but am getting nothing. I've tried:
query = new BasicDBObject("age", new BasicDBObject("$gt", "20"), new BasicDBObject("name", "AAA"));
JSON which i want to delete is like this.
{"school" : "NewSchool" , "name" : "AAA" , "age" : "50"}

What you want is the find-term:
{
"name" : "AAA",
"age" : { $gt : 20 }
}
Construct this as your basic DB object, or simply use the new 3.x Filters to create the Bson for you. (As I personally only use 3.x, here's the appropriate example):
MongoClient client = ...
MongoDatabase db = client.getDatabase(...);
MongoCollection<Document> coll = db.getCollection(...);
coll.deleteMany(Filters.and(Filters.eq("name", "AAA"), Filters.gt("age", 20)));

MongoDB Date query JAVA

Im trying to do a query to get all the values from my DB wich each have a date. One example:
leadTime: [
{
date: ISODate("2014-03-19T23:00:00Z"),
value: 25.8
},
{
date: ISODate("2014-03-20T23:00:00Z"),
value: 31.299999999999997
},
{
date: ISODate("2014-03-21T23:00:00Z"),
value: 34.4
}
]
enter code here
My code is:
DBObject query=new BasicDBObject("group",group);
DBObject serieData= col.findOne(query,new BasicDBObject(serie, 1));
if (serieData != null) {
List<DBObject> data = (List<DBObject>) serieData.get(serie);
for (DBObject item : data) {
result.add(new HistoryData((Date) item.get("date"),(Double) item.get("value")));
}
Now I want to get the values that the date is bigger than a date that I pass by parameter. The query I did is this:
DBObject query=new BasicDBObject("group",group)
.append("date", new BasicDBObject("$gte", parameterDate))
;
But I always receive the result empty, can you help me? sorry for my english and than

Assuming that leadTime is a field in your documents, your query has to look like this
DBObject query=new BasicDBObject("group",group)
.append("leadTime.date", new BasicDBObject("$gte", parameterDate))
;
The way you did it, MongoDB would have searched for a date field in your document root:
{ _id: "Foo",
date: ISODate("2014-03-19T23:00:00Z"),
[...]
}
Queries in MongoDB don't make a difference if the queried field is a single value or an array, so using the dot notation on a field which holds an array of subdocuments is perfectly valid.

What you want to do is not possible with a simple query.
But if you still want to do it in mongodb you need to use the aggregation framework, with something like that :
db.<col_name>.aggregate( [ { $unwind : "$group" }, { $match : {'group.date': { $gte : parameterDate } } ] )
this a js command, but you should be able to translate it easly in Java Driver (you can also add a $project operation to just return needed fields).

How to access nested element of mongo query result using Java and R?

I am using Java and R to fetch data from my database and implement prediction. My json in mongodb is like:
{
"Server" : [
{
"deviceName" : "NEWSCVMM",
"availability" : 100,
"osVersion" : "6.3.9600",
"averageResponseTime" : 0.422,
"useswapmemory" : "983040",
"freeswapmemory" : "983040",
"model" : "Virtual Machine",
"numberOfCpu" : "1",
"vendor" : "Microsoft Corporation",
"vmList" : [ ],
"macadd" : [ ],
"cpuInfo" : "Intel(R) Xeon(R) CPU X5670 # 2.93GHz",
"memory" : "6188596",
"serialNo" : "00252-00000-00000-AA228",
"cpuUtilization" : 0,
}]
}
I want to access cpuUtilization from that json. I tried to access nested values using (.) but get result as NULL. I also tried to execute same on R shell but get result as NULL.
Here is what I have tried so far:
c.eval("query <- dbGetQuery(db,' mycollection','{\"hostId\":\"0.0.0.0\",\"windowsServer.cpuUtilization\":{\"$ne\":\"null\"},\"runtimeMillis\":{\"$ne\":\"null\"}}')");
c.eval("date <- query$runtimeMillis");
c.eval("host_id <- query$hostId");
c.eval("cpu <- query$Server.cpuUtilization");
c.eval("all_data<-data.frame(cpu,date)");
c.eval("training<- all_data");
c.eval("rf_fit<-randomForest(cpu~date,data=training,ntree=500)");
c.eval("new <- data.frame(date="+my_predicted_date+ ")");
c.eval("predictions<-predict(rf_fit,newdata=new)");
REXP memory_predictions= c.eval("predictions");
How do I access nested elements on either R shell or using java?

Dot notation should work in Java, I have been using it for quite a while now.
Check your code carefully, there might be a slight mistake somewhere.
Can you please post a part of your code here? I can then take a look and comment.
Here is what I normally do -
Lets say my document is like this -
{_id:0, start : {x:10, y:50}, end : {x:20, y:100}}
{_id:1, start : {x:20, y:50}, end : {x:30, y:100}}
{_id:2, start : {x:30, y:50}, end : {x:40, y:100}}
If I want to query based on "x" value in start field, I would write something like this:
MongoClient client = new MongoClient();
DB db = client.getDB("YourDBNAME");
DBCollection collection = db.getCollection("YOURCOLLECTIONAME");
QueryBuilder builder = QueryBuilder().start("start.x").greaterThan("20");
DBCursor cur = collection.find(builder.get());
while(cursor.hasNext())
{
System.out.println(cursor.next());
}
Compare this code snippet with yours and see. You should get it working fine.
Let me know if this helps or you need more help on this.

MongoDB nested documents searching

How do I search through mongodb documents where documents have nested documents. For example I have a collection of private messages. Each private message has two nested documents - one representing the sending user and the other representing the receiving use. Both nested documents have the form -
userID: 34343,
name: Joe Bloggs
I would like to be able to search for all mail messages sent by a user (e.g. search the sender user nested document).
I am using the java driver. Do I need to create a DBObject which represents the nested document?
Thanks

As i understand u have document structure like this:
{
"someProperty" : 1,
"sendingUser" : {
userID : 34343,
name : "Joe Bloggs"
},
"recivingUser" : {
userID : 34345,
name : "Joe Bloggs"
}
}
So if you need find sending user with userID = 34345 you just need do following(i just think that is so, because actually i am working with c# driver for mongo):
DBCollection coll = db.getCollection("privateMessages")
query = new BasicDBObject();
query.put("sendingUser.userID", new BasicDBObject("$eq", 34345));
cur = coll.find(query); // all documents with sendingUser.userID = 34345 will be //returned by cursor
Also check tutorial for java driver

For MongoDB Java Driver v3.2.2. You can do something like this:
FindIterable<Document> iterable = collection.find(Document.parse("{\"sendingUser.userID\": \"34343\"}"));
FindIterable<Document> iterable = collection.find(Document.parse("{\"sendingUser.name\": \"Joe Bloggs\"}"));
You can put the $eq inside the JSON style query string. Like { <field>: { $eq: <value> } }.