使用Google App Engine数据存储区中的实体列表

Question

I am using objectify with Google App Engine (backed by their datastore project). I am a little confused on how lists of entities work.

I have some Student entities, and I have some Teacher entities.

I want the Teacher to have a students property that is List of Student entities.

It seems easy and it seems to work ok. However, I just noticed today that when I modify a property of a Student , it doesn't seems to update the Student in the various Teacher 's students List. For example, if I change a student's name and save it, the student list from a teacher will still have its old name. It is almost as if the teacher has its own local version of that object.

Is that correct? Is there any way that I can get the actual object stored? Or do I have to do something like just store the IDs?

Any help would be appreciated.

Here are the classes, for reference:

@Entity
@Index
public class StudentObj {
    @Id public Long id;
    public String StudentName;
}

@Entity
@Index
public class TeacherObj {
    @Id public Long id;
    public String TeacherName;
    public List<StudentObj> students;
}

Thanks in advance!

Answer 1

By using List<Student> , you are embedding the student data in the teacher object. To create a link to an independent entity, store a List<Key<Student>> or a List<Ref<Student>> in your teacher.