使用ObjectDB搜索空用户数据库时出现问题 [英] Problems searching empty user database with ObjectDB
本文介绍了使用ObjectDB搜索空用户数据库时出现问题的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我创建了一个使用ObjectDB创建和维护一组数据库的java应用程序。我目前正在尝试实现一个DB来存储由用户名和密码字符串组成的用户对象。在JFrame / swing类上，我有一个用于创建新用户的按钮，当点击此按钮时，我想要发生以下事件：
- 创建（或连接到）数据库
- 搜索数据库以查看是否存在具有提供的用户名的用户对象
- 如果用户已存在， ，否则创建用户
但是，当点击这个按钮时，我得到一个User not found查询对象的结果。我相信它是因为我有一个空数据库，但我想让代码第一次运行程序，因此它需要处理一个空数据库。我试图更改代码，以在首次运行查询之前创建一个新用户，然后该代码如何在每次点击按钮时都能工作，并且它可以检测是否需要创建新用户。
我试图创建一个默认或管理类型的用户，所以搜索会工作，但这意味着每次重复默认程序运行，这显然是一个不需要的功能，我不能做查询检查数据库是否为空（所以我只能创建默认用户在程序的第一次运行），因为这是问题我
所以，对于有ObjectDB经验的人，有没有办法处理空数据库搜索的情况？
这是代码的相关部分：
public class FrameLogIn extends JFrame {
private JPanel contentPane;
private String username;
char [] password;
private static EntityManager em;
/ **
*启动应用程序。
* /
public static void main（String [] args）{
EventQueue.invokeLater（new Runnable（）{
public void run（）{
try {
FrameLogIn frame = new FrameLogIn（）;
frame.setVisible（true）;
} catch（Exception e）{
e.printStackTrace $ b}
}
}）;
}
/ **
*创建框架。
* /
public FrameLogIn（）{
EntityManagerFactory emf =
Persistence.createEntityManagerFactory（user.odb）;
em = emf.createEntityManager（）;
final JTextField txtUsername = new JTextField（）;
txtUsername.setFont（new Font（Segoe UI Light，Font.PLAIN，30））;
txtUsername.setHorizontalAlignment（SwingConstants.CENTER）;
txtUsername.setToolTipText（username）;
txtUsername.setText（）;
txtUsername.setBounds（220，30，177，52）;
contentPane.add（txtUsername）;
txtUsername.setColumns（10）;
final JPasswordField passwordField = new JPasswordField（）;
passwordField.setFont（new Font（Tahoma，Font.PLAIN，30））;
passwordField.setHorizontalAlignment（SwingConstants.CENTER）;
passwordField.setBounds（220，93，177，52）;
contentPane.add（passwordField）;
JButton btnNewUser = new JButton（New user）;
btnNewUser.addActionListener（new ActionListener（）{
public void actionPerformed（ActionEvent e）{
username = txtUsername.getText（）;
password = passwordField.getPassword （）;
System.out.println（username）;
TypedQuery< Long> q = em.createQuery（
SELECT COUNT（u）FROM User u
+WHERE u.name ='+ username +'，Long.class）;
if（q.getSingleResult（）> 0）{
JOptionPane.showMessageDialog （contentPane.getParent（），具有此名称的用户已存在。）;
} else {
em.getTransaction（）。begin（）;
用户newUser = new User username，password.toString（））;
em.persist（newUser）;
em.getTransaction（）。commit（）;
JOptionPane.showMessageDialog（contentPane.getParent created。）;
}
}
}）;
btnNewUser.setFont（new Font（Segoe WP Semibold，Font.PLAIN，25））;
btnNewUser.setBackground（Color.WHITE）;
btnNewUser.setBounds（71，175，149，63）;
contentPane.add（btnNewUser）;
}
}
>
线程AWT-EventQueue-0中的异常[ObjectDB 2.5.3_03] SELECT COUNT（u）FROM ==> User< == u WHERE u.name =''
javax.persistence.PersistenceException
在com.objectdb.jpa找不到类型用户（错误301）
（位置21）。 JpaQuery.getSingleResult（JpaQuery.java:723）
at sg.FrameLogIn $ 2.actionPerformed（FrameLogIn.java:113）
at javax.swing.AbstractButton.fireActionPerformed（未知来源）
at javax .swing.AbstractButton $ Handler.actionPerformed（未知源）
at javax.swing.DefaultButtonModel.fireActionPerformed（未知源）
at javax.swing.DefaultButtonModel.setPressed（未知源）
at javax .swing.plaf.basic.BasicButtonListener.mouseReleased（未知源）
at java.awt.Component.processMouseEvent（未知源）
at javax.swing.JComponent.processMouseEvent（未知源）
在java.awt.Component.processEvent（未知源）
在java.awt.Container.processEvent（未知源）
在java.awt.Component.dispatchEventImpl（未知源）
在java .awt.Container.dispatchEventImpl（未知源）
at java.awt.Component.dispatchEvent（未知源）
at java.awt.LightweightDispatcher.retargetMouseEvent（未知源）
at java.awt .LightweightDispatcher.processMouseEvent（未知源）
at java.awt.LightweightDispatcher.dispatchEvent（未知源）
at java.awt.Container.dispatchEventImpl（未知源）
at java.awt.Window .dispatchEventImpl（未知源）
at java.awt.Component.dispatchEvent（未知源）
at java.awt.EventQueue.dispatchEventImpl（未知源）
at java.awt.EventQueue.access $ 200（未知源）
在java.awt.EventQueue $ 3.run（未知源）
在java.awt.EventQueue $ 3.run（未知源）
在java.security.AccessController。 doPrivileged（native方法）
at java.security.ProtectionDomain $ 1.doIntersectionPrivilege（未知源）
at java.security.ProtectionDomain $ 1.doIntersectionPrivilege（未知源）
at java.awt.EventQueue $ 4 .run（Unknown Source）
at java.awt.EventQueue $ 4.run（Unknown Source）
at java.security.AccessController.doPrivileged（Native方法）
at java.security.ProtectionDomain $ 1 。未知来源）
at java.awt.EventQueue.dispatchEvent（未知源）
at java.awt.EventDispatchThread.pumpOneEventForFilters（未知源）
at java.awt.EventDispatchThread.pumpEventsForFilter （未知源）
at java.awt.EventDispatchThread.pumpEventsForHierarchy（未知源）
at java.awt.EventDispatchThread.pumpEvents（未知源）
at java.awt.EventDispatchThread.pumpEvents源）
在java.awt.EventDispatchThread.run（未知源）
导致：com.objectdb.o.TEX：类型未找到用户
at com.objectdb.o.MSG .e（MSG.java:107）
at com.objectdb.o.TRS.g（TRS.java:212）
at com.objectdb.o.SYR.q（SYR.java:259 ）
at com.objectdb.o.SYR.n（SYR.java:188）
at com.objectdb.o.QRC。< init>（QRC.java:152）
at com.objectdb.o.QRM.U6（QRM.java:250）
at com.objectdb.o.MST.U6（MST.java:933）
at com.objectdb.o.WRA .U6（WRA.java:293）
at com.objectdb.o.WSM.U6（WSM.java:114）
at com.objectdb.o.QRR.g（QRR.java:245 ）
at com.objectdb.o.QRR.f（QRR.java:154）
at com.objectdb.jpa.JpaQuery.getSingleResult（JpaQuery.java:716）
...谢谢，也为了记录我不会存储明文密码，我只是试图解决方案如果实体类不在数据库中，可能会发生这种情况
如果这似乎是原因，可以定义一个持久化单元或在查询之前将类引入ObjectDB，例如：
em.getMetamodel（）。entity（User.class）;
I am creating a java application which uses ObjectDB to create and maintain a set of databases. I'm currently trying to implement a DB to store user objects consisting of username and password strings. On a JFrame/swing class I have a button for creating new users, when this button is clicked, I want the following to happen:
- Create (or connect to) database
- Search the database to see if a user object exists with supplied username
- if user already exists show a dialog message, otherwise create the user
However, when this button is clicked I get a 'User not found' error on the line which uses the results from the query object. I'm pretty sure it's because I have an empty database, however I want the code to work for the first time the program is ran, so it needs to handle an empty database. I've tried changing the code to create a new user before the query is first run, then the code works how I want it to each time the button is clicked, and it can detect whether or not a new user needs to be created.
I tried to create a 'default' or 'admin' type user so the search would work, however this means a repeat 'default' user will be created every time the program is ran, which is obviously an unwanted feature, and I can't do a query to check if the database is empty (so I could only create the default user on the first run of the program), because that is the problem I was having in the first place!
So, to anyone experienced with ObjectDB, is there a way I can handle the case where an empty database is searched?
Here's the relevant parts of my code:
public class FrameLogIn extends JFrame {
private JPanel contentPane;
private String username;
char[] password;
private static EntityManager em;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
FrameLogIn frame = new FrameLogIn();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public FrameLogIn() {
EntityManagerFactory emf =
Persistence.createEntityManagerFactory("user.odb");
em = emf.createEntityManager();
final JTextField txtUsername = new JTextField();
txtUsername.setFont(new Font("Segoe UI Light", Font.PLAIN, 30));
txtUsername.setHorizontalAlignment(SwingConstants.CENTER);
txtUsername.setToolTipText("username");
txtUsername.setText("");
txtUsername.setBounds(220, 30, 177, 52);
contentPane.add(txtUsername);
txtUsername.setColumns(10);
final JPasswordField passwordField = new JPasswordField();
passwordField.setFont(new Font("Tahoma", Font.PLAIN, 30));
passwordField.setHorizontalAlignment(SwingConstants.CENTER);
passwordField.setBounds(220, 93, 177, 52);
contentPane.add(passwordField);
JButton btnNewUser = new JButton("New user");
btnNewUser.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
username = txtUsername.getText();
password = passwordField.getPassword();
System.out.println(username);
TypedQuery<Long> q = em.createQuery(
"SELECT COUNT(u) FROM User u "
+ "WHERE u.name = '" + username + "'", Long.class);
if (q.getSingleResult()>0) {
JOptionPane.showMessageDialog(contentPane.getParent(), "A user with this name already exists.");
} else {
em.getTransaction().begin();
User newUser = new User(username, password.toString());
em.persist(newUser);
em.getTransaction().commit();
JOptionPane.showMessageDialog(contentPane.getParent(), "User created.");
}
}
});
btnNewUser.setFont(new Font("Segoe WP Semibold", Font.PLAIN, 25));
btnNewUser.setBackground(Color.WHITE);
btnNewUser.setBounds(71, 175, 149, 63);
contentPane.add(btnNewUser);
}
}
and the error:
Exception in thread "AWT-EventQueue-0" [ObjectDB 2.5.3_03] SELECT COUNT(u) FROM ==> User <== u WHERE u.name = ''
javax.persistence.PersistenceException
Type User is not found (error 301)
(position 21) at com.objectdb.jpa.JpaQuery.getSingleResult(JpaQuery.java:723)
at sg.FrameLogIn$2.actionPerformed(FrameLogIn.java:113)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$200(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
Caused by: com.objectdb.o.TEX: Type User is not found
at com.objectdb.o.MSG.e(MSG.java:107)
at com.objectdb.o.TRS.g(TRS.java:212)
at com.objectdb.o.SYR.q(SYR.java:259)
at com.objectdb.o.SYR.n(SYR.java:188)
at com.objectdb.o.QRC.<init>(QRC.java:152)
at com.objectdb.o.QRM.U6(QRM.java:250)
at com.objectdb.o.MST.U6(MST.java:933)
at com.objectdb.o.WRA.U6(WRA.java:293)
at com.objectdb.o.WSM.U6(WSM.java:114)
at com.objectdb.o.QRR.g(QRR.java:245)
at com.objectdb.o.QRR.f(QRR.java:154)
at com.objectdb.jpa.JpaQuery.getSingleResult(JpaQuery.java:716)
... 37 more
Thanks, also for the record i will not be storing plaintext passwords, I'm just trying to get a basic DB working before I start implementing hashed passwords.
解决方案 This could happen if the entity class is not in the database yet (no instances of that class have been persisted yet), and a persistence unit is not defined.
If this seems to be the cause, either define a persistence unit or introduce the class to ObjectDB before the query, for example by:
em.getMetamodel().entity(User.class);
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