无法在@ID @generatevalue JPA实体上接受NULL值

Question

我正在尝试为我的应用添加“添加到愿望清单”功能，但始终收到此错误：

Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.3.2.v20111125-r10461):           org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: java.sql.SQLIntegrityConstraintViolationException: Column 'WISH_ID'        cannot accept a NULL value.
Error Code: -1
Call: INSERT INTO WISHLIST (BOOK_TITLE, CUSTOMER_ID) VALUES (?, ?)
bind => [2 parameters bound]
Query: InsertObjectQuery(dukesbookstore.entity.Wishlist[ wishId=null ])

ENTITY课程：

@Entity
@Table(name = "WISHLIST")
@XmlRootElement
@NamedQueries(
{
@NamedQuery(name = "Wishlist.findByCustomerId", query = "SELECT w FROM Wishlist w WHERE  w.customerId = :customerId"),

})
public class Wishlist implements Serializable
{
private static final long serialVersionUID = 1L;
@Id @GeneratedValue(strategy=GenerationType.IDENTITY) 
@Column(name = "WISH_ID")
private Integer wishId;
@Column(name = "CUSTOMER_ID")
private Integer customerId;
@Size(max = 35)
@Column(name = "BOOK_TITLE")
private String bookTitle;

public Wishlist()
{
}



public Integer getCustomerId()
{
    return customerId;
}

public void setCustomerId(Integer customerId)
{
    this.customerId = customerId;
}

public String getBookTitle()
{
    return bookTitle;
}

public void setBookTitle(String bookTitle)
{
    this.bookTitle = bookTitle;
}   
}

这是创建新愿望的代码：

public void createWishlist(String title,int cust_id)
{
            Wishlist newWish = new Wishlist();
            newWish.setBookTitle(title);
            newWish.setCustomerId(cust_id);
            em.persist(newWish);
  }

我试图查看其他类似的问题，但是它们涉及到我未使用的休眠状态。 我也尝试了各种生成策略，例如AUTO ， SEQUENCE ， TABLE但是都失败了。 我还有另一个名为customer的实体，该实体完全相同，但是尽管它是通过表单创建的，但效果很好。

更改为AUTO产生此错误：

Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.3.2.v20111125-r10461):   org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: java.sql.SQLSyntaxErrorException: Table/View 'SEQUENCE' does not exist.
Error Code: -1
Call: UPDATE SEQUENCE SET SEQ_COUNT = SEQ_COUNT + ? WHERE SEQ_NAME = ?
bind => [2 parameters bound]
Query: DataModifyQuery(name="SEQUENCE" sql="UPDATE SEQUENCE SET SEQ_COUNT = SEQ_COUNT + ? WHERE SEQ_NAME = ?")
root cause

java.sql.SQLSyntaxErrorException: Table/View 'SEQUENCE' does not exist.
root cause

org.apache.derby.client.am.SqlException: Table/View 'SEQUENCE' does not exist.

Persistence.xml，以防相关

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence"  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence    http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
<persistence-unit name="myStorePU" transaction-type="JTA">
    <jta-data-source>mydb</jta-data-source>
    <class>myStore.entity.Book</class>
    <class>myStore.entity.Customer</class>
    <class>myStore.entity.Wishlist</class>

    <properties>
        <property name="javax.persistence.jdbc.user" value="APP"/>
        <property name="javax.persistence.jdbc.password" value="APP"/>

         <property name="eclipselink.logging.level" value="FINE"/>
    </properties>

</persistence-unit>

Answer 1

终于可以了

首先，我必须删除从netbeans db创建工具创建的表，该表具有这样的创建代码，如使用“抓取结构”所示

create table "APP".WISHLIST
(
WISH_ID NUMERIC(5) not null primary key,
CUSTOMER_ID NUMERIC(5),
BOOK_TITLE VARCHAR(100)
)

其次，我将此代码添加到我的persistence.xml文件中

<property name="eclipselink.ddl-generation" value="create-tables"/>

这可以解决问题，因为它是由自己创建的表，具有不同的创建代码，从自动创建的抓取结构可以看出：

create table "APP".WISHLIST
(
WISH_ID INTEGER default GENERATED_BY_DEFAULT not null primary key,
CUSTOMER_ID NUMERIC(5),
BOOK_TITLE VARCHAR(100)
)

因此，基本上应该让netbeans从实体创建表本身，但是我使用的是“从表创建实体”功能，为此我必须首先在netbeans gui中创建表。

谢谢@Geziefer的所有帮助，我也从您的帮助中学到了很多。

Answer 2

在JPA单表继承问题中，这可能是“非可空属性” 。 指定它可能会有所帮助，并且不会造成伤害

@JoinTable(name = "[some join table name]",
    joinColumns = {@JoinColumn(name = "[some ID column name]")},
    inverseJoinColumns = {@JoinColumn(name = "[some different ID column name]")})