@reference and error : @Id field cannot be nul

[lolveley]

hello

I have 2 pojos (in java) , each one has an Id as objectId, and a field marked as @reference with a collection of the other class.

to be more clear, say the two pojos are users of computers and computers; an user can open a session on many computers and a computer can have sessions of many users opened.

when I try to create an user, with its fields, and a computer, and I link them via their ArrayList fields, I have this error :

@Id field cannot be null.

here is some code, a little simplier than what I explained:

pojo1 : a car

**********************************************************************

@Entity
public class Voiture {
 
	@Id ObjectId id;
	String immatriculation;
	@Reference
	Conducteur conducteur;
 
 
 
 
 
	public String getImmatriculation() {
		RETURN immatriculation;
	}
	public void setImmatriculation(String immatriculation) {
		this.immatriculation = immatriculation;
	}
	public Conducteur getConducteur() {
		RETURN conducteur;
	}
	public void setConducteur(Conducteur conducteur) {
		this.conducteur = conducteur;
	}
	public Voiture(String immatriculation) {
		super();
		this.immatriculation = immatriculation;
	}
	@Override
	public String toString() {
		RETURN "Voiture [immatriculation=" + immatriculation + "]";
	}
	public ObjectId getId() {
		RETURN id;
	}
	public void setId(ObjectId id) {
		this.id = id;
	}
 
 
 
 
}

**********************************************

pojo2 : a driver

**********************************************
@Entity
public class Conducteur {
 
	@Id ObjectId id;
	String nom;
	Integer bonus;
	@Reference
	ArrayList<Voiture> voitures;
 
 
 
 
	public String getNom() {
		RETURN nom;
	}
	public void setNom(String nom) {
		this.nom = nom;
	}
	public Integer getBonus() {
		RETURN bonus;
	}
	public void setBonus(Integer bonus) {
		this.bonus = bonus;
	}
	public ArrayList<Voiture> getVoitures() {
		RETURN voitures;
	}
	public void setVoitures(ArrayList<Voiture> voitures) {
		this.voitures = voitures;
	}
 
	public void addVoiture(Voiture to_add){
		voitures.ADD(to_add);
	}
	public Conducteur() {
		super();
		voitures=new ArrayList<Voiture>();
	}
	@Override
	public String toString() {
		RETURN "Conducteur [nom=" + nom + "]";
	}
 
 
 
}
**********************************************

the main class:
**********************************************
Morphia morphia = new Morphia();
 
morphia.map(Voiture.class).map(Conducteur.class);
 
Datastore ds = morphia.createDatastore("Voitures_conducteurs");
 
Conducteur jean = new Conducteur();
jean.setNom("jean");
jean.setBonus(25);
 
Voiture porsche=new Voiture("211 XB 57");
 
jean.addVoiture(porsche);
porsche.setConducteur(jean);
 
 
 
ds.save(jean);


could you tell me if I have to generate an Id for the referenced class; and could you explain me how to solve this dilemna : class A contains a reference on B, B contains a reference on A, I have to save one of the two classes before the other and then the other class has no Id generated (it's by this way I understood the error message).

thanks,

olivier SAINT-EVE

[Scott Hernandez]

Just change your entities to declare the id field with an initial value:

@Id ObjectId id = new ObjectId();

The id will be assigned during your save, but not by the server. So
either way the client will have to create the ObjectId.

[lolveley]

hi scott

I understood your answer but I have a question : if I create the objectId at the same time as the creation of the class, how the computer can set a objectId different than the objectId already stored in the base? I mean are the objectId differents one from another? how is it made?

[Scott Hernandez]

I'm not sure I understand. Here is a description of what an ObjectId
is: http://www.mongodb.org/display/DOCS/Object+IDs

They are like UUIDs and you can create many at the same time and they
will all be different.

[lolveley]

thank you, it worked.

I understood. objectId are like ISBN for books : an unique identifier, and it's not generated like in RDMS, I mean the new objectId does not depand of those which are already stored.

thanks

olivier