Hibernate JPA IdentifierGenerationException：使用@embeddedid为类生成的空id [英] Hibernate JPA IdentifierGenerationException: null id generated for class with @embeddedid

问题描述

在一种情况下，我的数据库域模型映射到程序实体时遇到问题，在这种情况下，实体本质上是一个连接两个其他实体（时隙和一天）的连接表（一个时段）。另一个实体（一节课）然后提及这个期间实体，确定它何时发生。

当我尝试使用<$ c保存新课程的课程时$ c> saveOrUpdate（lesson） hibernate抛出一个IdentifierGenerationException异常

$ b

org.hibernate.id.IdentifierGenerationException：null id生成的：class com.trials.domain.Period

数据库如下所示（不是真正的数据库，只是关键表和栏目）

在java hibernate模型中，我使用了嵌入ID作为句点类的主键，然后课程类引用了句点。

Period.java

  @Entity 
 @ Table（name =period）
 public class Period {
 @EmbeddedId 
 private PeriodId periodId; 
 
 @ManyToOne（fetch = FetchType.EAGER）
 @JoinColumn（name =day_idday，nullable = false，insertable = false，updatable = false）
 private Day Day; 
 
 @ManyToOne（fetch = FetchType.EAGER）
 @JoinColumn（name =timeslot_idtimeslot，nullable = false，insertable = false，updatable = false）
私人Timeslot时隙; 
 
 //构造函数，getters，setters，hashcode，等于
} 
  

嵌入式ID仅包含主键列：

PeriodId.java

  @Embeddable 
 public class PeriodId implements Serializable {
 @Column（name =timeslot_idtimeslot）
 private int timeslotId; 
 
 @Column（name =day_idday）
 private int dayId; 
 
 //构造函数，getters，setters，hashcode，等于
} 
  

然后是课程类，它使用定义为的时间段：

Lesson.java

  @Entity 
 @Table（name =lesson）
 public class Lesson {
 @Id 
 @ Column（name =idlesson）
 private int lessonId; 
 $ b @ManyToOne（fetch = FetchType.LAZY，cascade = CascadeType.ALL）
 @JoinColumns（{@ JoinColumn（name =period_timeslot_idtimeslot，nullable = false，updatable = false） JoinColumn（name =period_day_idday，nullable = false，updatable = false）}）
 private期间期间; 
 //构造函数，getters，setters，hashcode，等于
} 
  

Timeslot和Day实体类都是非常基本的pojos，它们的id使用 GenerationType.AUTO 。所以我的问题是：

1. 导致此IdentifierGenerationException的原因


2. 如何避免它同时保持不变数据库模型
   

预先感谢

解决方案

把这些人放在一起

  @ManyToOne（fetch = FetchType.EAGER）
 @JoinColumn（name =day_idday ，nullable = false，insertable = false，updatable = false）
 private Day day; 
 
 @ManyToOne（fetch = FetchType.EAGER）
 @JoinColumn（name =timeslot_idtimeslot，nullable = false，insertable = false，updatable = false）
私人Timeslot时隙; 
  

并丢弃这些整数。我以这种方式完成了一个类似于你的映射，并且它可以工作。

I am having trouble mapping my database domain model to the program entities in one case where the entity is essentially a join table (a period) which combines two other entities (a timeslot and a day). Another entity (a lesson) then has a reference to this period entity, determining when it occurs.

When I try to save a lesson with a new period using saveOrUpdate(lesson) hibernate throws an IdentifierGenerationException

org.hibernate.id.IdentifierGenerationException: null id generated for:class com.trials.domain.Period

The database looks like below (not the real database, just the key tables and columns)

In the java hibernate model, I have used an embedded id for the primary key of the period class and the lesson class then has a reference to a period.

Period.java

@Entity
@Table(name = "period")
public class Period{
    @EmbeddedId
    private PeriodId periodId;

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "day_idday", nullable = false, insertable = false, updatable = false)
    private Day day;

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "timeslot_idtimeslot", nullable = false, insertable = false, updatable = false)
    private Timeslot timeslot;

    //constructors, getters, setters, hashcode, and equals
}

And the embedded id just has the primary key columns:

PeriodId.java

@Embeddable
public class PeriodId implements Serializable {
    @Column(name = "timeslot_idtimeslot")
    private int timeslotId;

    @Column(name = "day_idday")
    private int dayId;

    //constructors, getters, setters, hashcode, and equals
}

Then there is the lesson class that uses the period defined as:

Lesson.java

@Entity
@Table(name = "lesson")
public class Lesson {
    @Id
    @Column(name = "idlesson")
    private int lessonId;

    @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinColumns({@JoinColumn(name = "period_timeslot_idtimeslot", nullable = false, updatable = false), @JoinColumn(name = "period_day_idday", nullable = false, updatable = false)})
    private Period period;
    //constructors, getters, setters, hashcode, and equals
}

The Timeslot and Day entity classes are both very basic pojos, and their ids use GenerationType.AUTO. So my problems are:

1. What causes this IdentifierGenerationException
2. How to avoid it while keeping the same database model

Thanks in advance

解决方案

Put those guys

@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "day_idday", nullable = false, insertable = false, updatable = false)
private Day day;

@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "timeslot_idtimeslot", nullable = false, insertable = false, updatable = false)
private Timeslot timeslot;

inside the PeriodId class and throw away those ints. I have done a mapping similar to yours this way and it works.

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