title: bidirectional one-to-one relationship (mappedBy)
body: <blockquote>
    <p>You create a <strong>bidirectional one-to-one relationship</strong> 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.</p>
  </blockquote>
  
  <p>What can a <strong>bidirectional one-to-one relationship</strong> do? <P>
  Can someone give me a example?</p>
  
  <p>And why I always got this error.</p>
  
  <blockquote>
    <p>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")!!</p>
  </blockquote>
  
  <p>Thanks in advance!</p>