JPA Self Join using JoinTable

Question

I have 1 entity call Item in which I want to be able to link parent items to children. to use a join table to create a parent/child relationship. I haven\'t been able to g

Answer 1

I believe @JoinTable is only allowed on a @OneToOne or @OneToMany or @ManyToMany, I don't think it makes any sense on a @ManyToOne. Use a @JoinColumn, or a @OneToOne.

Also your @OneToMany does not make sense, the mappedBy must be an attribute and you have no parentItem, it should be parent, and parent should use a @JoinColumn.

Answer 2

Try to use @JoinColumninstead:

 @ManyToOne(optional = true, fetch = FetchType.LAZY)
 @JoinColumn(name = "PARENTITEMID", referencedColumnName = "ITEMID")
 private Item parent;

 @OneToMany(
        cascade = {CascadeType.ALL},
        orphanRemoval = true,
        fetch = FetchType.LAZY
 )
 @JoinColumn(name = "PARENTITEMID")
 private List<Item> children;

Answer 3

After a lot of reading on JPA 2.0 I figured out that I needed a newer version of Eclipselink 2.3+ in order to support what I was trying to do. Here is the code that actually worked in my case, but it will not work due to our dependency on an older version [EclipseLink 2.0.2]. Also another project's is still using Toplink-essentials JPA 1.0 which again does like this notation.

public class Item {

@ManyToOne(optional = true, fetch = FetchType.LAZY)
@JoinTable(name = "ITEMINCENTIVESMAPPING", 
        joinColumns = { @JoinColumn(name = "INCENTIVEITEMID", referencedColumnName = "ITEMID", insertable = false, updatable = false) }, 
        inverseJoinColumns = { @JoinColumn(name = "ITEMID", referencedColumnName = "ITEMID", insertable = false, updatable = false) } )
private Item parentItem;

@OneToMany(fetch = FetchType.LAZY)
@JoinTable(name = "ITEMINCENTIVESMAPPING", 
        joinColumns = { @JoinColumn(name = "INCENTIVEITEMID", referencedColumnName = "ITEMID") }, 
        inverseJoinColumns = { @JoinColumn(name = "ITEMID", referencedColumnName = "ITEMID") } )
private List<Item> items;

}