在Morphia和MongoDB中使用泛型

Question

简短说明：

我在将mongo DB中的文档读入具有泛型属性的java类时遇到了困难。错误显示java.lang.double不能强制转换为com.mongodb.dbobject

@Getter @Setter @NoArgsConstructor @Entity("randomDataCollection")
public class RandomDataCollection {

    @Id
    private ObjectId id = new ObjectId();

    private String name;

    @Embedded
    private MyGenericProperty<Float> temperatureMumbai;

}

@Getter @Setter @NoArgsConstructor
public class MyGenericProperty<T> {

    private T value;

    private String unit;

}

MyGenericProperty<Float> temperatureMumbai = new MyGenericProperty<Float>();
temperatureMumbai.setValue(32.8f);
temperatureMumbai.setUnit("°C");

RandomDataCollection randomData = new RandomDataCollection();
randomData.setName("RandomData0711");
randomData.setTemperatureMumbai(temperatureMumbai);

Datastore datastore = getDatastore();
datastore.save(randomData);

...但是当我试着从数据库里读...

randomData = datastore.find(RandomDataCollection.class).filter("name =", "RandomData0711").get();

...我得到以下异常：

Caused by: java.lang.ClassCastException: java.lang.Double cannot be cast to com.mongodb.DBObject

我确实发现了一些关于泛型和morphia的讨论，但老实说，我不知道如何将这些应用到我的问题上。

我在运行Morphia 1.5.8

Answer 1

几乎可以肯定有更好的方法来做到这一点，但这对我很有效。

DBCursor cursor = datastore.find(RandomDataCollection.class).filter("name =", name).fetch().getCursor();
List<RandomDataCollection> list = new ArrayList<>();
while (cursor.hasNext()) {
    DBObject theObj = cursor.next();
    RandomDataCollection rec = new RandomDataCollection();
    rec.setId((ObjectId)theObj.get("_id"));
    MyGenericProperty<Float> temperatureMumbai = new MyGenericProperty<Float>();
    BasicDBObject x = (BasicDBObject)theObj.get("temperatureMumbai");
    temperatureMumbai.setValue(x.getFloat("value"));
    temperatureMumbai.setUnit(x.getString("unit"));
    rec.setTemperatureMumbai(temperatureMumbai);
    list.add(rec);
}