Inserting Java Object to MongoDB Collection Using Java

Question

I am trying to insert a whole Java object into a MongoDB Collection using Java. I am getting following error:

Error :

Exception in t         


        

Answer 1

I'm a little confused as to know why you'd think this would work in the first place. The first thing you need to know is how to map your POJO to a MongoDB document. Currently, you're not telling the system(your code) how to do that.

You can either use a mapping library for this (Morphia comes to mind) or use ReflectionDBObject. Either solution allows you to map POJO to MongoDB document or MongoDB document to POJO(the former way is a lot more nicely than the latter).

Answer 2

Pro
you continue to work with strong typed objects as you wanted to

Contra
Some people really dislike : extends

package foo;
import com.mongodb.BasicDBObject;


public class Employee extends BasicDBObject {

private static final long serialVersionUID = 2105061907470199595L;
//should be something shorter as "name" like "n" 
//here just use name to conform your  sample
public static final String NAME = "name";
public static final String NO = "no";
public static final String COLLECTION_NAME = "employee";

public Long getNo() {
    return getLong(NO);
}

public void setNo(long no) {
    put(NO, no);
}

public String getName() {
    return getString(NAME);
}

public void setName(String name) {
    put(NAME, name);
}


}

package foo;
import java.net.UnknownHostException;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.Mongo;
import com.mongodb.MongoException;


public class Test {

public static void main(String[] args) throws UnknownHostException,
        MongoException {

    Mongo mongo = new Mongo("localhost", 27017);
    DB db = mongo.getDB("yeahMongo");

    Employee employee = new Employee();
    employee.setNo(1L);
    employee.setName("yogesh");

    DBCollection employeeCollection = null ;
    employeeCollection = db.getCollection(Employee.COLLECTION_NAME);

    employeeCollection.save(employee);

    System.err.println(employeeCollection.findOne());

}


}

In addition to morphia you should take a look to jongo : http://jongo.org/ jongo use the same form syntax as js mongo engine, and I found it great point for a beginner. You don't have to switch your mental map between mongojs and java. you can use the js sample with little changes.

Answer 3

DB db = mongoClient.getDB( "mydb" );

coll = db.getCollection("testCollection");

Employee emp = new Employee();
emp.setId("1001");
emp.setName("John Doe");

//Converting a custom Class(Employee) to BasicDBObject
Gson gson = new Gson();
BasicDBObject obj = (BasicDBObject)JSON.parse(gson.toJson(emp));
coll.insert(obj);
findEmployee(new BasicDBObject("id","1001"));


public static void findEmployee(BasicDBObject query){

    DBCursor cursor = coll.find(query);

    try {
       while(cursor.hasNext()) {
          DBObject dbobj = cursor.next();
        //Converting BasicDBObject to a custom Class(Employee)
          Employee emp = (new Gson()).fromJson(dbobj.toString(), Employee.class);
          System.out.println(emp.getName());
       }
    } finally {
       cursor.close();
    }

}

I thought that it would be useful to post code that did conversions both ways.
Storing an Employee Object
Finding and re-creating an employee Object
Hope this is useful..

Answer 4

With MongoDB you cannot insert your Java bean in the DB, but you have to remap them to MongoDB Object.

In your case you have to do:

BasicDBObject basicDBObject = new BasicDBObject();
basicDBObject.put("no", employee.getNo());
basicDBObject.put("name", employee.getName());

Answer 5

I have the same error, when I try to insert a java BasicDBObject into a MongoDb Collection.

My object is created from a Xml converted to Json.

java.lang.IllegalArgumentException: can't serialize class net.sf.json.JSONNull
    at org.bson.BasicBSONEncoder._putObjectField(BasicBSONEncoder.java:299)
    at org.bson.BasicBSONEncoder.putMap(BasicBSONEncoder.java:339)
    at org.bson.BasicBSONEncoder._putObjectField(BasicBSONEncoder.java:261)

This error is caused by empty tags in Xml; when I removed all empty tags, then I solved it.