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 No SQL > Mongo DB > How to query a Collection

How to query a Collection 

MongoDB is a scalable, high-performance, open source NoSQL database. It offers Ad hoc queries, Indexing, Replication, Load balancing, File storage (GridFS), Aggregation, MapReduce and Server-side JavaScript execution. This requires the library mongo-2.8.0.jar to be present in the classpath. The following example shows how to query a collection.

File Name  :  mynums.json

File Name  :  
com/bethecoder/tutorials/mongodb/tests/QueryTest.java 
Author  :  Sudhakar KV
Email  :  kvenkatasudhakar@gmail.com
   
package com.bethecoder.tutorials.mongodb.tests;

import java.net.UnknownHostException;

import com.mongodb.BasicDBObject;
import com.mongodb.BasicDBObjectBuilder;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.DBCursor;
import com.mongodb.DBObject;
import com.mongodb.Mongo;
import com.mongodb.MongoException;

public class QueryTest {

  /**
   @param args
   */
  public static void main(String[] args) {

    try {
      //Connect to mongoDB with given IP and PORT
      Mongo mongo = new Mongo("localhost"27017);
      
      //Get the database object
      DB database = mongo.getDB("mytestdb");
      
      //Gets a collection with a given name.
      DBCollection collection = database.getCollection("mynums");

      //Query for  (num > 2 && num < 9) && (even==true)
      DBObject query = new BasicDBObject();
      query.put("num", BasicDBObjectBuilder.start().add("$gt"2).add("$lt"9).get())
      query.put("even"true);
      
      //Queries for all objects in this collection
      DBCursor dbCursor = collection.find(query);
      DBObject record = null;
      
      while (dbCursor.hasNext()) {
        record = dbCursor.next();
        System.out.println(record);
      }
      
    catch (UnknownHostException e) {
      e.printStackTrace();
    catch (MongoException e) {
      e.printStackTrace();
    }
  }
}
   

It gives the following output,
{ "_id" : 4 , "num" : 4 , "even" : true , "num^2" : 16.0}
{ "_id" : 6 , "num" : 6 , "even" : true , "num^2" : 36.0}
{ "_id" : 8 , "num" : 8 , "even" : true , "num^2" : 64.0}


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