無法在@ID @generatevalue JPA實體上接受NULL值

Question

我正在嘗試為我的應用添加“添加到願望清單”功能，但始終收到此錯誤：

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課程：

@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;
}   
}

這是創建新願望的代碼：

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

我試圖查看其他類似的問題，但是它們涉及到我未使用的休眠狀態。 我也嘗試了各種生成策略，例如AUTO ， SEQUENCE ， TABLE但是都失敗了。 我還有另一個名為customer的實體，該實體完全相同，但是盡管它是通過表單創建的，但效果很好。

更改為AUTO產生此錯誤：

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，以防相關

<?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

終於可以了

首先，我必須刪除從netbeans db創建工具創建的表，該表具有這樣的創建代碼，如使用“抓取結構”所示

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

其次，我將此代碼添加到我的persistence.xml文件中

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

這可以解決問題，因為它是由自己創建的表，具有不同的創建代碼，從自動創建的抓取結構可以看出：

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，基本上應該讓netbeans從實體創建表本身，但是我使用的是“從表創建實體”功能，為此我必須首先在netbeans gui中創建表。

謝謝@Geziefer的所有幫助，我也從您的幫助中學到了很多。

Answer 2

在JPA單表繼承問題中，這可能是“非可空屬性” 。 指定它可能會有所幫助，並且不會造成傷害

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