Question

For our project we have a layer architecture. The DAO-Layer communicates with the Database and gets the stored Entities. The Service-Layer communicates with the DAO-Layer to get the entities and implements more complex methods. Then the View-Layer communicates with the Serivce-Layer to get the needed information.

Part of the Entity:

@Entity
public class Operation implements Serializable {
private Integer id;

@GeneratedValue
@Id
public Integer getId() {
    return id;
}

public void setId(Integer id) {
    this.id = id;
}
private List<Participation> participations;

@OneToMany
public List<Participation> getParticipations() {
    return participations;
}

public void setParticipations(List<Participation> participations) {
    this.participations = participations;
}

DAO-Layer:

@Override
public Operation read(int id) {
    return this.em.find(Operation.class, id);
}

Service-Layer:

@Override
public Operation getOperation(Integer operationId)
{
    Operation operation = operationDAO.read(operationId);
    //operation.getParticipations();
    return operation;
}

View-Layer:

Operation o = opService.getOperation(operationId);

Using this without the operation.getParticipations(); on the View-Layer the participation-List is missing. If i add the stupid code then the object is forwarded correctly and the participation list is available.

I cant explain to myself why the object isn’t forwarded correctly? Can you help me? Thx in advance.

Edit: All other attributes/fields of the object are forwarded correctly (may important to know)

Answer 1

For @OneToMany default FetchType is LAZY.

And The LAZY strategy is a hint to the persistence provider that data should be fetched lazily when it is first accessed.