java - 执行 SELECT 查询时出现 ClassCastException

Question

目前，我将包含以下列的 CSV 文件上传到 Google App Engine 数据存储区:

id, roleName, eggName, highestAllTimePrice, lowestAllTimePrice, averagePrice

当我访问localhost:8888/_ah/admin/datastore时，表的结果如下:

Key, Write Ops, ID/Name, averagePrice, eggName, eggNumber, highestAllTimePrice, lowestAllTimePrice, roleName

我从表中获取所有数据如下:

public String GetData(final ModelMap model)
{
    EntityManager em = EMF.get().createEntityManager();
    Query q = em.createQuery("SELECT s FROM Egg s");
    List<Egg> eggs = new ArrayList<Egg>(q.getResultList());

    model.addAttribute("eggs", eggs);
    return "index";
}

实体

@Entity
public class Egg {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Key key;

    private int eggNumber;
    private String roleName;
    private String eggName;
    private double highestPrice;
    private double lowestPrice;
    private double averagePrice;

    // getters setters
}

但是当我运行该查询时，我收到此错误:

java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Double
    at com.google.appengine.datanucleus.FetchFieldManager.fetchDoubleField(FetchFieldManager.java:140)
    at org.datanucleus.state.AbstractStateManager.replacingDoubleField(AbstractStateManager.java:2256)
    at Entity.Egg.jdoReplaceField(Egg.java)
    at Entity.Egg.jdoReplaceFields(Egg.java)

问题是我不知道为什么要转换类型？我的实体类映射错误了吗？

Answer 1

也许您的双字段(highestPrice 等)被视为数据存储中的字符串，因此无法映射到您的实体。