I'm using Hibernate with annotations (in spring), and I have an object which has an ordered, many-to-one relationship which a child object which has a composite primary key, one component of which is a foreign key back to the id of the parent object.
The structure looks something like this:
+=============+ +================+
| ParentObj | | ObjectChild |
+-------------+ 1 0..* +----------------+
| id (pk) |-----------------| parentId |
| ... | | name |
+=============+ | pos |
| ... |
+================+
I've tried a variety of combinations of annotations, none of which seem to work. This is the closest I've been able to come up with:
@Entity
public class ParentObject {
@Column(nullable=false, updatable=false)
@Id @GeneratedValue(generator="...")
private String id;
@OneToMany(mappedBy="parent", fetch=FetchType.EAGER, cascade={CascadeType.ALL})
@IndexColumn(name = "pos", base=0)
private List<ObjectChild> attrs;
...
}
@Entity
public class ChildObject {
@Embeddable
public static class Pk implements Serializable {
@Column(nullable=false, updatable=false)
private String parentId;
@Column(nullable=false, updatable=false)
private String name;
@Column(nullable=false, updatable=false)
private int pos;
@Override
public String toString() {
return new Formatter().format("%s.%s[%d]", parentId, name, pos).toString();
}
...
}
@EmbeddedId
private Pk pk;
@ManyToOne
@JoinColumn(name="parentId")
private ParentObject parent;
...
}
I arrived at this after a long bout of experimentation in which most of my other attempts yielded entities which hibernate couldn't even load for various reasons.
UPDATE: Thanks all for the comments; I have made some progress. I've made a few tweaks and I think it's closer (I've updated the code above). Now, however, the issue is on insert. The parent object seems to save fine, but the child objects are not saving, and what I've been able to determine is that hibernate is not filling out the parentId part of the (composite) primary key of the child objects, so I'm getting a not-unique error:
org.hibernate.NonUniqueObjectException:
a different object with the same identifier value was already associated
with the session: [org.kpruden.ObjectChild#null.attr1[0]]
I'm populating the name
and pos
attributes in my own code, but of course I don't know the parent ID, because it hasn't been saved yet. Any ideas on how to convince hibernate to fill this out?
Thanks!
The Manning book Java Persistence with Hibernate has an example outlining how to do this in Section 7.2. Fortunately, even if you don't own the book, you can see a source code example of this by downloading the JPA version of the Caveat Emptor sample project (direct link here) and examining the classes Category
and CategorizedItem
in the auction.model
package.
I'll also summarize the key annotations below. Do let me know if it's still a no-go.
ParentObject:
@Entity
public class ParentObject {
@Id @GeneratedValue
@Column(name = "parentId", nullable=false, updatable=false)
private Long id;
@OneToMany(mappedBy="parent", fetch=FetchType.EAGER)
@IndexColumn(name = "pos", base=0)
private List<ChildObject> attrs;
public Long getId () { return id; }
public List<ChildObject> getAttrs () { return attrs; }
}
ChildObject:
@Entity
public class ChildObject {
@Embeddable
public static class Pk implements Serializable {
@Column(name = "parentId", nullable=false, updatable=false)
private Long objectId;
@Column(nullable=false, updatable=false)
private String name;
@Column(nullable=false, updatable=false)
private int pos;
...
}
@EmbeddedId
private Pk id;
@ManyToOne
@JoinColumn(name="parentId", insertable = false, updatable = false)
@org.hibernate.annotations.ForeignKey(name = "FK_CHILD_OBJECT_PARENTID")
private ParentObject parent;
public Pk getId () { return id; }
public ParentObject getParent () { return parent; }
}