Question

You create a bidirectional one-to-one relationship using fields on
both classes, with an annotation on the child class’s field to declare
that the fields represent a bidirectional relationship. The field of
the child class must have a @Persistent annotation with the argument
mappedBy = “…”, where the value is the name of the field on the
parent class. If the field on one object is populated, then the
corresponding reference field on the other object is populated
automatically.

What can a bidirectional one-to-one relationship do?

Can someone give me a example?

And why I always got this error.

Class “com.example.datastore.Employee” has field “contactInfo” with
“mapped-by” specified as “contactInfo”. This field doesnt exist in the
target of the relation (“com.example.datastore.ContactInfo”)!!

Thanks in advance!

Answer 1

First the Error
What the error is saying is that contactInfo is not a field of class com.example.datastore.ContactInfo . They field mapped by must be a field\property of the class you are mapping to .

Second The concept of Bi-Direction Mapping

It’s just that two tables in one-to-one or one-to-many relationship where both entities will have knowledge of the other s. You do not always need it and that depends on situation and context but generally is more common to have bi-directional one to many than one to one.
You question is about one-to-one so to give you an example of when both entities need to know about each other from Hibernate docs A bidirectional one-to-one association on a join table is possible, but extremely unusual. But if you really wanted to be able to get either entiy from which ever table (which is very rare) then you create bi-directional one to one

Person and Address just to quote an example