Morphia 与我的映射 JAVA Class

Question

我正在尝试使用吗啡做一个简单的 findOne()。我的代码如下：

public static void main(String[] args)
{
    MongoClient client = new MongoClient();
    Morphia morphia = new Morphia();
    morphia.map(Restaurant_M.class);
    Datastore ds = morphia.createDatastore(client, "test");
    System.out.println(ds.find(Restaurant_M.class).get());
    client.close();
}

我打印出一个空值。我无法找到出了什么问题。有人能指出我正确的方向吗？谢谢。

编辑 Collection格式

{
    "_id" : ObjectId("572eb5df1d739cc73c21f953"),
    "address" : {
            "building" : "469",
            "coord" : [
                    -73.961704,
                    40.662942
            ],
            "street" : "Flatbush Avenue",
            "zipcode" : "11225"
    },
    "borough" : "Brooklyn",
    "cuisine" : "Hamburgers",
    "grades" : [
            {
                    "date" : ISODate("2014-12-30T00:00:00Z"),
                    "grade" : "A",
                    "score" : 8
            },
            {
                    "date" : ISODate("2014-07-01T00:00:00Z"),
                    "grade" : "B",
                    "score" : 23
            },
            {
                    "date" : ISODate("2013-04-30T00:00:00Z"),
                    "grade" : "A",
                    "score" : 12
            },
            {
                    "date" : ISODate("2012-05-08T00:00:00Z"),
                    "grade" : "A",
                    "score" : 12
            }
    ],
    "name" : "Wendy'S",
    "restaurant_id" : "30112340"
}

@实体class

@Entity("restaurants")
public class Restaurant_M
{
    @Id
    public ObjectId _id;
    @Property("borough")
    public String town;
    public String cuisine;
    public String name;
    @Property("restaurant_id")
    public String r_id;

Answer 1

问题是您没有提供有关实体所需的所有信息您可以只使用映射到实体： dt.getCollection(Restaurant_M.class);然后使用 DBObject 要么 dt.createQuery(Restaurant_M.class).field("").equal("to specify").get;

Answer 2

我做了一个DBO实现如下：

 public Restaurant_M getByID (String id)
 {
    Query<Restaurant_M> query = createQuery().field("cuisine").equal(id);
    return query.get();
 }

并按如下方式更新了主要方法并且有效

public static void main(String[] args)
{
    MongoClient client = new MongoClient("127.0.0.1:27017");
    Morphia morphia = new Morphia();
    Datastore ds = morphia.createDatastore(client, "test");
    RestaurantDAO rdao = new RestaurantDAOImpl(Restaurant_M.class, ds);
    Restaurant_M r = rdao.getByID("Hamburgers");
    System.out.println(r);

    r = ds.find(Restaurant_M.class).get();
    System.out.println (r);

}

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