Get names of all keys name in collection using Java

Question

In this collection (called "play")

{ "_id" : 0 , "outlook" : "sunny" , "temp" : "hot" , "humidity" : "high" , "windy" : "weak" , "lable" : "no"}
{ "_id" : 1 , "outlook" : "sunny" , "temp" : "hot" , "humidity" : "high" , "windy" : "strong" , "lable" : "no"}
{ "_id" : 2 , "outlook" : "overcast" , "temp" : "hot" , "humidity" : "high" , "windy" : "weak" , "lable" : "yes"}
{ "_id" : 3 , "outlook" : "rain" , "temp" : "mild" , "humidity" : "high" , "windy" : "weak" , "lable" : "yes"}
{ "_id" : 4 , "outlook" : "rain" , "temp" : "cool" , "humidity" : "normal" , "windy" : "weak" , "lable" : "yes"}
{ "_id" : 5 , "outlook" : "rain" , "temp" : "cool" , "humidity" : "normal" , "windy" : "strong" , "lable" : "no"}

How can I retrieve the names of the keys using Java?

Example output:

[ "_id" , "outlook" , "temp" , "humidity" , "windy" , "lable" ]

The code looks like this so far

public class test {
    public static void main(String[] args) {
        DB dbtest = connection.dbconn();
        DBCollection collection = dbtest.getCollection("play");
        BasicDBObject allQuery = new BasicDBObject();;

        DBCursor cursor = collection.find(allQuery);
        while (cursor.hasNext()) {
            System.out.println(cursor.next());
        }

     /**
       write code.. here...
     */   
    }
}

We're not going to write the code for you. You're already off to a good start, why don't you try assigning `cursor.next()` to a variable and see what you can do with that variable. — David says Reinstate Monica, Dec 01 '15 at 14:41
I'm voting to close this question as off-topic because SO is not a code-writing service. — Marco Bonelli, Dec 01 '15 at 14:46
@MarcoBonelli: Maybe he just needs a little pointer to the API. — serv-inc, Dec 01 '15 at 14:47
@user then it should be rephrased to be on-topic, because what I see right now is only "please write this code for me". — Marco Bonelli, Dec 01 '15 at 14:49
can you try this code in mongoshell **doc=db.thinks.findOne(); for (key in doc) print(key);** — mohamedzajith, Dec 01 '15 at 14:53
@mohamedzajith: For a mongoshell solution see http://stackoverflow.com/questions/2298870/mongodb-get-names-of-all-keys-in-collection?rq=1 — serv-inc, Dec 01 '15 at 14:55
@MarcoBonelli Answer is working I got the Answer which expected — mohamedzajith, Dec 01 '15 at 15:05

serv-inc · Accepted Answer · 2015-12-01T15:02:07.210

3

If you look in the API at DBCursor.next(), it returns a DBObject, which is a subtype of BSONObject with a keySet() method. That field is a Set<String>, with the description

The names of the fields in this object

Thus, you might be able to use

for (String key: cursor.next().keySet()) {
    // do whatever with the key name here, f.ex.
    System.out.println(key);
}

edited Dec 01 '15 at 15:02

answered Dec 01 '15 at 14:46

serv-inc

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Get names of all keys name in collection using Java

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