Mongo ManyToMany Mapping - Embedded Object when Expecting Id

brianhyder · **Joined:** Thu Sep 12, 2013 9:17 pm **Posts:** 2

Hey,

I'm having a little trouble getting the expected result out of a simple many to many mapping.

First things first - dependencies:
org.hibernate.ogm:hibernate-ogm-mongodb:4.0.0.Beta1
org.mongodb:mongo-java-driver:2.11.2
org.springframework.data:spring-data-mongodb:1.2.3.RELEASE

Code:

import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.ManyToMany;

import org.springframework.data.annotation.Id;

@Entity
public class A {

   @Id
   public String id;
   
   @ManyToMany
   public Set<B> bs;
}

Code:

import javax.persistence.Entity;

import org.springframework.data.annotation.Id;

@Entity
public class B {
   
   @Id
   public String id;
   
   
   public String ts = "ssklskl";
   
   public String shss = "hssla";
}

Code:

                A a = new A();
      template.save(a);
      
      B b = new B();
      template.save(b);
      
      a = template.findById(a.id, A.class);
      b = template.findById(b.id, B.class);
      Set<B> bs = new HashSet<B>();
      bs.add(b);
      a.bs = bs;
      
      template.save(a);

The Result when using the command line:

Code:

{ "_id" : ObjectId("523264e291fddeedcb688d2f"), "_class" : "com.beelite.beans.A", "bs" : [     {     "_id" : ObjectId("523264e291fddeedcb688d30"),     "ts" : "ssklskl",     "shss" : "hssla" } ] }

I haven't changed any of the defaults. I was expecting just the IDs to be embedded and not the whole object. Am I missing something in my mapping?

Thanks in advance,

Brian

DavideD · **Joined:** Fri Sep 09, 2011 3:18 am **Posts:** 295

Hi brianhyder,

In general, this way of mapping collections offers better performance for read operations and the document can be retrieved with a single database operation.

You can change the way collections are stored in MongoDB using the option hibernate.ogm.mongodb.associations.store
More details about it in the documentation: http://docs.jboss.org/hibernate/ogm/4.0/reference/en-US/html/ogm-datastore-providers.html#d0e1875

I hope this has been helpful.

Davide

brianhyder · **Joined:** Thu Sep 12, 2013 9:17 pm **Posts:** 2

Hey,

Thanks for the quick reply. I have a couple of follow up items.

1) The documentation specifies the properties but how/where to set them. I am currently using spring data on top of OGM and have a spring configuration (see below) but cannot figure out how to set the properties:

Code:

   <!-- Default bean name is 'mongo' -->
   <mongo:mongo host="xxx.xxx.xxx.xxx" port="27017" >
      <!-- OPTIONAL: configure <mongo:options /> -->
   </mongo:mongo>

   <mongo:db-factory dbname="dbtest" mongo-ref="mongo" />

   <bean id="mongoTemplate" class="org.springframework.data.mongodb.core.MongoTemplate">
      <constructor-arg ref="mongoDbFactory" />
   </bean>

2) The default "store" is listed as IN_ENTITY according the documentation at the link you provided in section 5.3.2.2. The example provided is what I would expect from the code I posted in the original question but instead I'm seeing the "B" object nested within the "A" object. I'm curious if I'm misinterpreting the documentation, the documentation is wrong, or if there is a bug in the OGM code.

3) I went one step further with my sample code I provided earlier (see below). When I delete the "B" object instance the persisted "A" object is not updated to reflect the deletion of the "B" instance. Is this expected behavior? Does this behavior change if the "store" is changed?

Code:

A a = new A();
      template.save(a);
      
      B b = new B();
      template.save(b);
      
      a = template.findById(a.id, A.class);
      b = template.findById(b.id, B.class);
      Set<B> bs = new HashSet<B>();
      bs.add(b);
      a.bs = bs;
      
      template.save(a);
      
      template.remove(b);
      
      a = template.findById(a.id, A.class);

Sorry for all the followup. I'm really interested in this framework and want to make sure I'm using it correctly.

-Brian

Gunnar · **Joined:** Sat Jan 24, 2009 12:46 pm **Posts:** 388

Hi Brian,

Refer to http://docs.jboss.org/hibernate/ogm/4.0/reference/en-US/html/ogm-configuration.html#_bootstrapping_hibernate_ogm to find out how to configure OGM; basically you specify any properties either in persistence.xml or you set them programmatically on your OgmConfiguration when using the native Hibernate APIs.

I'm wondering about your usage of OGM *and* Spring Data MongoDB at the same time, though. Both provide their own means for accessing MongoDB, so you should be using either of them but not both at the same time. As your example uses Spring Data's MongoTemplate, OGM won't be involved at all.

--Gunnar