Question

为什么我得到这个异常？

package com.domain.idea;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;
import javax.persistence.Table;
import org.hibernate.annotations.AccessType;
/**
 * object model for the view [InvestmentReturn].[vMAE_MFE]
 */
@Entity
@Table(name="vMAE_MFE", schema="InvestmentReturn")
@AccessType("field")
public class MAE_MFEView
{
    /**
     * trade property is a SuggestdTradeRecommendation object
     */
    @OneToOne(fetch = FetchType.LAZY , cascade = { CascadeType.PERSIST })
    @JoinColumn(name = "suggestedTradeRecommendationID")
    private SuggestedTradeRecommendation trade;
    /**
     * Most Adeverse Excursion value
     */
    private int MAE;
    public int getMAE()
    {
        return MAE;
    }
    /**
     * Most Favorable Excursion value
     */
    private int MFE;
    public int getMFE()
    {
        return MFE;
    }
    /**
     * @return trade property
     * see #trade
     */
    public SuggestedTradeRecommendation getTrade()
    {
        return trade;
    }
}

更新：我已经改变了我的代码看起来像这样：

package com.domain.idea;
import javax.persistence.CascadeType;
import javax.persistence.FetchType;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;
import javax.persistence.Table;
import org.hibernate.annotations.AccessType;
/**
 * object model for the view [InvestmentReturn].[vMAE_MFE]
 */
@Entity
@Table(name="vMAE_MFE", schema="InvestmentReturn")
@AccessType("field")
public class MAE_MFEView
{
    /**
     * trade property is a SuggestdTradeRecommendation object
     */
    @Id
    @OneToOne(fetch = FetchType.LAZY , cascade = { CascadeType.PERSIST })
    @JoinColumn(name = "suggestedTradeRecommendationID")
    private SuggestedTradeRecommendation trade;
    /**
     * Most Adeverse Excursion value
     */
    private int MAE;
    public int getMAE()
    {
        return MAE;
    }
    /**
     * Most Favorable Excursion value
     */
    private int MFE;
    public int getMFE()
    {
        return MFE;
    }
    /**
     * @return trade property
     * see #trade
     */
    public SuggestedTradeRecommendation getTrade()
    {
        return trade;
    }
}

但现在我得到这个异常：

Caused by: org.hibernate.MappingException: Could not determine type for: com.domain.idea.SuggestedTradeRecommendation, at table: vMAE_MFE, for columns: [org.hibernate.mapping.Column(trade)]
    at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:292)
    at org.hibernate.mapping.SimpleValue.isValid(SimpleValue.java:276)
    at org.hibernate.mapping.RootClass.validate(RootClass.java:216)
    at org.hibernate.cfg.Configuration.validate(Configuration.java:1135)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1320)
    at org.hibernate.cfg.AnnotationConfiguration.buildSessionFactory(AnnotationConfiguration.java:867)
    at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:669)
    ... 145 more

524

264

75

14

Answer 1

您缺少一个用@Id注释的字段。每个@Entity都需要一个@Id-这是数据库中的主键。

如果你不希望你的实体被保存在一个单独的表中，而是成为其他实体的一部分，你可以使用@Embeddable而不是@Entity。

如果您只希望一个数据传输对象来保存来自休眠实体的一些数据，则无论如何都不要在其上使用注释-将其保留为简单的 pojo。

更新：关于 SQL 视图，Hibernate 文档写：

Hibernate 映射的视图和基表之间没有区别。这在数据库级别是透明的

Answer 2

对我来说，应该使用javax.persistence.Id而不是org.springframework.data.annotation.Id。对于遇到此问题的任何人，您可以检查是否导入了正确的Id类。

Answer 3

当您为 @ Id 导入与Javax.persistance.Id不同的库时，可能会引发此错误;您可能需要注意这种情况

在我的情况下，我有

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Table;
import org.springframework.data.annotation.Id;
@Entity
public class Status {
    @Id
    @GeneratedValue
    private int id;

当我改变这样的代码，它得到了工作

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Table;
import javax.persistence.Id;
@Entity
public class Status {
    @Id
    @GeneratedValue
    private int id;

Answer 4

下面的代码可以解决 NullPointerException。

@Id
@GeneratedValue
@Column(name = "STOCK_ID", unique = true, nullable = false)
public Integer getStockId() {
    return this.stockId;
}
public void setStockId(Integer stockId) {
    this.stockId = stockId;
}

如果你添加@Id，那么你可以声明一些更像上面声明的方法。