package database.one; //let's say this one is my production database.

/**
* @hibernate.class table="A"
*/

public class A {
private String id;
/**
  * @hibernate.id column="id"
  * generator-class="sequence"
  */
public String getId() { return id; }
public void setId(String id) { this.id = id; }
}

package database.two; //let's say this other is my development database.

/**
* @hibernate.class table="B"
*/

public class B{
private A a;
/**
  * @hibernate.many-to-one column="id"
  * class="database.one.A"
  * unique="true"
  */
public A getA() { return a; }
public void setA(A a) { this.a = a; }
}