休眠多对一合并

Question

I have a class Person with id, name, and status . the status is a class Status with id, and status string this is shortly the code generated by netbeans tool for hibernate

class Person{
   long id;
   String name;
   Status status;
   //getters and setters
}
class Status{
   long id;
   String status;
   List<Person> persons;
   //getters and setters
}

the problem is when I want to merge a person in the session I get the status null

Person p = getById(1L); // person name=XX; status=1

p.setName("YY");

session.merge(p); // here the status is get NULL not-null property references a null or transient value: model.Status

I know that hibernate load the person object when merging so why the status return as null;??

Answer 1

In this case status is not null, but it's transient. You're trying to merge Person before merging the Status that the person contains. So you're trying to introduce in the hibernate context an entity that has a reference outside the context. The solution is either merging the status before merging the person or defining CascadeType.MERGE .

Answer 2

Lazy loading only works when the many-to-one reference is using the other object's primary key. And also be avoid of creating your architecture on one2many relations.

Use like that in your person.hbm.xml file.

<set name="status" table="status" 
            inverse="true" lazy="false" fetch="select">
        <key>
            <column name="id" not-null="true" />
        </key>
        <one-to-many class="xxx.Status" />
 </set>

and status.hbm.xml should be like that;

 <many-to-one name="person" class="xxx.Person" fetch="select">
      <column name="id" not-null="true" />
 </many-to-one>

i hope it helps.