count number of column in mongoDB using Java

Question

I have installed MongoDB in my system and I inserted 10 documents into the username collection. That document contains name, roll no, city fields. I need to count the number of fields in the username collection.

I except 3... How to get the 3 from java program?

Tug Grall · Accepted Answer · 2014-09-02 12:59:15Z

1

If you are using Java in your application you are manipulating DBObject ( http://api.mongodb.org/java/2.6/com/mongodb/DBObject.html ) and you can get the KeySet from this and the size will be the number of attributes. (in your case it will be 4 since you have the _id attribute)

But this is PER DOCUMENT, remember that in a collection, each document can have its own "structure", in your case one user could have 4 attributes, another could have 10... and some of them could have sub documents with their own structure. MongoDB does not have any "catalog".

Some system are "sampling" the data to analyze the global structure of the documents and provide a catalog but this is will not be exact.

answered Sep 2, 2014 at 12:59

Tug Grall

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ThomasCle · Accepted Answer · 2014-09-02 13:16:01Z

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Try this:

System.out.println(coll.getCount());

More Detail here: http://docs.mongodb.org/ecosystem/tutorial/getting-started-with-java-driver/

edited Sep 2, 2014 at 13:16

ThomasCle

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answered Sep 2, 2014 at 12:21

Indrajeet Singh

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1 Comment

BasK Over a year ago

System.out.println(coll.getCount()); this command only get the number of row in the db.. I got the solution cursor.next().toMap().keySet().size();

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