昨天遇到一个问题，我无法连接到 derby 数据库（很可能是由于 persistence.xml 问题）我被引导修改我的 persistence.xml，使其包含两个额外的属性；
<property name="eclipselink.ddl-generation" value="create-tables" />
<property name="eclipselink.ddl-generation.output-mode" value="database" />
添加它们后，我不会遇到一堆错误，例如SCHEMA "xx" doesn't exist或Unknown entity bean class: class model.Userbay, please verify that this class has been marked with the @Entity annotation.
尽管现在一切都很好，但我意识到事实并非如此。起初我试图通过实体管理器的 .find() 方法从数据库中获取其中一行。经过一段时间的测试以从数据库中检索记录后，我认为尝试将某些内容插入数据库并查看会发生什么可能会更好。执行了以下代码行；
emgr.createNativeQuery("insert into ADRIAN.USERBAY (USER_NAME, PASSWORD, EMAIL, FIRST_NAME, LAST_NAME) values('testts123s', '1', '1', '1', '1')").executeUpdate();
我注意到数据库中没有插入任何内容...但是尝试执行 .find() 以查找我刚刚插入的主键（testts123s）它找到了记录（尽管在数据源资源管理器中数据库的表没有' t 填充此记录）。因此我的问题是我被链接到一个空表会发生什么？
以下是代码；
持久性.xml
<?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="EJBAuctionv2">
<!-- <jta-data-source>JDBC/MyDB</jta-data-source> -->
<class>model.Userbay</class>
<class>model.Item</class>
<class>model.Category</class>
<properties>
<property name="javax.persistence.jdbc.password" value="123" />
<property name="javax.persistence.jdbc.user" value="adrian" />
<property name="javax.persistence.jdbc.driver" value="org.apache.derby.jdbc.EmbeededDriver" />
<property name="javax.persistence.jdbc.url" value="jdbc:derby:C:\Users\Adrian\MyDB;create=true" />
<!-- <property name="eclipselink.ddl-generation" value="create-tables" />
<property name="eclipselink.ddl-generation.output-mode" value="database" /> -->
</properties>
</persistence-unit>
</persistence>
用户注册会话Bean
package auction;
import javax.ejb.EJB;
import javax.ejb.LocalBean;
import javax.ejb.Remote;
import javax.ejb.Singleton;
import javax.ejb.Stateful;
import javax.ejb.Stateless;
import javax.management.Query;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import model.Userbay;
/**
* Session Bean implementation class userRegistrationSB
*/
@Remote @Stateless
public class userRegistrationSB implements userRegistrationSBRemote {
//@EJB private Userbay user;
@PersistenceContext(name = "EJBAuctionv2") private EntityManager emgr;
/**
* Default constructor.
*/
public userRegistrationSB() {}
@Override
public boolean registerUser(String username, String password, String email,
String firstname, String lastname) {
boolean registered = false;
//emgr.createNativeQuery("insert into ADRIAN.USERBAY (USER_NAME, PASSWORD, EMAIL, FIRST_NAME, LAST_NAME) values('testts123s', '1', '1', '1', '1')").executeUpdate();
System.out.println("Registering an user with username: " + username);
Userbay user = emgr.find(model.Userbay.class, username);
if (user == null) {
System.out.println("Username doesn't exist.");
registered = true;
} else {
registered = false;
System.out.println("Username already exists.");
}
return registered;
}
@Override
public boolean userExists(String username) {
return false;
}
@Override
public boolean userMatchesPassword(String username, String password) {
return false;
}
}
Userbay 实体 Bean
package model;
import java.io.Serializable;
import javax.persistence.*;
import java.util.List;
@Entity @Table (name = "Userbay")
@NamedQuery(name="Userbay.findAll", query="SELECT u FROM Userbay u")
public class Userbay implements Serializable {
private static final long serialVersionUID = 1L;
@Id @GeneratedValue (strategy = GenerationType.TABLE)
@Column(name="USER_NAME")
private String userName;
private String email;
@Column(name="FIRST_NAME")
private String firstName;
@Column(name="LAST_NAME")
private String lastName;
@Column(name="PASSWORD")
private String password;
//bi-directional many-to-one association to Item
@OneToMany(mappedBy="userbay")
private List<Item> items;
public Userbay() {
}
public String getUserName() {
return this.userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public String getEmail() {
return this.email;
}
public void setEmail(String email) {
this.email = email;
}
public String getFirstName() {
return this.firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return this.lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getPassword() {
return this.password;
}
public void setPassword(String password) {
this.password = password;
}
public List<Item> getItems() {
return this.items;
}
public void setItems(List<Item> items) {
this.items = items;
}
public Item addItem(Item item) {
getItems().add(item);
item.setUserbay(this);
return item;
}
public Item removeItem(Item item) {
getItems().remove(item);
item.setUserbay(null);
return item;
}
}