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...
 }