Hi

I am quite new to JPA/Hibernate (Java in general) so my question is as follows (note, I have searched far and wide and have not come across an answer to this):

I have two entities:

Parent and Child (naming changed).

Parent contains a list of Children and Children refers back to parent.

e.g.

@Entity
public class Parent {

@Id
@Basic
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "PARENT_ID", insertable = false, updatable = false)
private int id;        

    /* ..... */

    @OneToMany(cascade = { CascadeType.ALL }, fetch = FetchType.LAZY)
    @JoinColumn(name = "PARENT_ID", referencedColumnName = "PARENT_ID", nullable = true)
    private Set<child> children;

    /* ..... */

}

@Entity
public class Child {

@Id
@Basic
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "CHILD_ID", insertable = false, updatable = false)
private int id; 

    /* ..... */

    @ManyToOne(cascade = { CascadeType.REFRESH }, fetch = FetchType.EAGER, optional = false)
@JoinColumn(name = "PARENT_ID", referencedColumnName = "PARENT_ID")
private Parent parent;

    /* ..... */

}

I want to be able to do the following:

1. Retrieve a Parent entity which would contain a list of all its children (List), however, when listing Parent (getting List, it of course should omit the children from the results, therefore setting FetchType.LAZY.

2. Retrieve a Child entity which would contain an instance of the Parent entity.

Using the code above (or similar) results in two exceptions:

1. Retrieving Parent: A cycle is detected in the object graph. This will cause infinitely deep XML...

2. Retrieving Child: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: xxxxxxxxxxx, no session or session was closed

When retrieving the Parent entity, I am using a named query (i.e. calling it specifically) @NamedQuery(name = "Parent.findByParentId", query = "SELECT p FROM Parent AS p LEFT JOIN FETCH p.children where p.id = :id")

Code to get Parent (i.e. service layer): public Parent findByParentId(int parentId) { Query query = em.createNamedQuery("Parent.findByParentId"); query.setParameter("id", parentId);

    return (Parent) query.getSingleResult();
}

Why am I getting a LazyInitializationException event though the List property on the Parent entity is set as Lazy (when retrieving the Child entity)?