首先要记一下根据 DBREF 的ObjectId 以及根据 ref 集合为条件查询问题.

在不同的可视化客户端里面显示的问题.

//某客户端显示这样,直接CMD查询也是这样显示.这样我无法看懂find条件 {     "_id" : ObjectId("58ae865f7dde420cd0eae39f"),     "className" : "com.thesys.morphia.dbref.DbrefTest$Book",     "price" : "60.0",     "author" : DBRef("Author", ObjectId("58ae865f7dde420cd0eae39e"))}

换了一个客户端

//同一个数据显示的格式,根据这样尝试查询 {    "_id" : ObjectId("58ae865f7dde420cd0eae39f"),    "className" : "com.thesys.morphia.dbref.DbrefTest$Book",    "price" : "60.0",    "author" : {        "$ref" : "Author",        "$id" : ObjectId("58ae865f7dde420cd0eae39e")    }}

以下两个shell均可查询

db.Book.find({"author.$ref":"Author"})db.Book.find({
    "author.$id":ObjectId("58ae865f7dde420cd0eae39e")})

以下是我的测试代码,使用morphia

 

@RunWith(JUnit4.class)public class DbrefTest {        static final Morphia morphia = new Morphia();    static final Datastore datastore = morphia.createDatastore(new MongoClient(),"BookTest");    @Entity    static class Book{        @Id        private ObjectId id;//id        private String name;//书名        private double price;//价格        @Reference        private Author author;     }    @Entity    static class Author{        @Id        private ObjectId id;//id        private String name;//作者名称        private String nationality;//国籍    }        public static void main(String[] args) {        Author author = new Author();        author.setName("大仲马");        author.setNationality("法国");        datastore.save(author);        Book book = new Book();        book.setAuthor(author);        datastore.save(book);    }        @Test    public void testQuery(){        Query
     
       query = datastore.createQuery(Book.class);        System.out.println(query.count());        List
      
        books = query.asList();        System.out.println(books.get(0).getAuthor().getName());    }        @Test    public void testUpdate(){        //注意根据ID查询不能传入String 必须是ObjectId        Query
       
         query = datastore.createQuery(Book.class).field("_id").equal(new ObjectId("58ae7f837dde423968454e62"));//        System.out.println(query.get().price);//直接获取结果集第一个//        datastore.get(Book.class,new ObjectId("58ae7f837dde423968454e62")).price //直接根据ID查询一个文档        UpdateOperations
        
          updateOperation = datastore.createUpdateOperations(Book.class).set("name","三个火枪手").set("price", 55);        datastore.updateFirst(query, updateOperation);//.更新第一个找到的    }    　　//聚合管道,投射　　@Test　　public void testAggregation(){
    　　　　//把price 重命名为 name　　　　AggregationPipeline aggregationPipeline = datastore.createAggregation(Book.class).project(Projection.projection("name","price"));　　　　Iterator
         
           books = aggregationPipeline.aggregate(Book.class);　　　　System.out.println(books.next().getName());//打印出name : 60.0　　}}