That is good post..well i am having a problem and it is driving me nuts.
i have a scenario in which each product it link to some other product.
table = product
id (primary key),
link(pointing to id)
this link can and cannot be null.its kind of parent child relation in one table..after searching and found nothing i thought may b my design is bad so i split the product table
table = product
id

table = pr_link
prod_id ()
link_id ()
both are foreign keys from product table.
is it one to one relation and iam unable to fix it..please help thank you..

What's the problem with the first design?

Don't use NOT NULL constraints on the 'link' column in your database and don't place nullable = false on the @OneToOne annotation.
The link reference in your article object maybe null, so this shouldn't be a problem.

The second approach would have to be used for a one-to-many relation but might work for a one-to-one relation as well. You just need a @JoinTable on your relation.

hi..
let me finish it..sorry for late reply
i have product table in which i have both new and second hand products , new product may have and may not have second hand product.i call second hand product as link . the problem was that second hand product (link) again refer to product table..it is like parent child in one table...

now product table look like this

product
pid
link
.
i have fixed it by doing following mapping...
@OneToOne
@JoinColumn(name="link")
private ProductImpl productLink;

thanks.