mongodb morphia关联查询一例

//...此处省略了import...
/**
 * Created by shenzhigang on 4/15/16.
 */
public class Main {
    public static void main(String[] args) {
        Datastore datastore;
        final Morphia morphia = new Morphia();
        morphia.mapPackage("com.bdb.datatypes.common.po");
        datastore = morphia.createDatastore(new MongoClient("localhost", 27017), "test001");
        datastore.ensureIndexes();

        Student student = new Student();
        student.setName("沈志刚");
        student.setAge(30);

        School school = new School();
        school.setName("苏州小学");
        school.setAddress("苏州市");
        datastore.save(school);

        student.setSchool(school);
        datastore.save(student);

        List<Key<School>> schools =datastore.createQuery(School.class).field("name").equal("苏州小学").asKeyList();
        List<Student> studentList =  datastore.find(Student.class).field("school").in(schools).asList();
    }
}

@Entity
class Student {
    @Id
    private ObjectId objectId ;
    private String name;
    private int age;
    @Reference
    private School school;
　　//...此处省略了get set.... 
}

@Entity
class School {
    @Id
    private ObjectId objectId;
    private String address;
    private String name;
　　//....此处省略了get set...
}