JPA EntityManager不會在SQLite數據庫中提交更改

Question

我有一個SQLite數據庫。我使用EclipseLink和JPA使用它。另外我有一個實體類User：

import com.vaadin.server.VaadinService; 
import java.io.Serializable; 
import javax.persistence.*; 

@Entity 
public class User implements Serializable { 

    @Id @GeneratedValue 
    long id;   // Unique identifier of the user in the DB 
    String username; // Unique name used for login 
    String password; // Password used for login 

    public User() { 
    } 

    public User(String username, String password) { 
     this.username = username; 
     this.password = password; 
    } 

    public Long getId() { 
     return id; 
    } 

    public String getUsername() { 
     return username; 
    } 

    public void setUsername(String username) { 
     this.username = username; 
    } 

    public String getPassword() { 
     return password; 
    } 

    public void setPassword(String password) { 
     this.password = password; 
    } 
} 

在登記表我創建了一個用戶，然後調用EntityManager到persist()的變化：

public int createUser(String username, String password, String password_confirmation) { 
     int regStatus = 0; 
     if(checkValidUsername(username)) { 
      if(checkValidPassword(password, password_confirmation)) { 
       EntityManager em = factory.createEntityManager(); 
       try { 
        em.getTransaction().begin(); 
         User user = new User(username, password); 
         em.persist(user); 
        em.getTransaction().commit(); 
       } 
       catch(Exception e) { 
        System.out.println(e.getMessage()); 
        regStatus = 3; 
       } 
       finally { 
        em.close(); 
       } 
      } 
      else regStatus = 2; // Password mismatch 
     } 
     else regStatus = 1;  // User with selected username already present in DB 

     return regStatus; 
    } 

它的工作沒有任何問題。我在USER表中獲得每個新註冊的用戶。但是，當我嘗試更改密碼時，它不起作用。下面是與此相關的程序方法：

// Inside the controller for my settings view - here the user can change various things related to his/her profile 
public void setCurrentUser() { 
    currentUser = UserController.findUserByName((String)VaadinSession.getCurrent().getAttribute("username")); // findUserByName() is a static method 
} 


// Inside the User controller I have multiple methods for common user-related queries; here I use the username that I have retrieved from the VaadinSession's attribute "username" to execute a query and get the User entity (I make sure that a user's name is unique so getting a single result here is not a problem) 
public static User findUserByName(String username) { 
    if(username == null) return null; 
    factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME); 
    EntityManager em = factory.createEntityManager(); 
    User user = null; 

    try{ 
     Query q = em.createQuery("SELECT u FROM User u WHERE u.username = :username"); 
     q.setParameter("username", username); 
     user = (User)q.getSingleResult(); 

    } 
    catch(Exception e){ 
     System.err.println(e.getMessage()); 
    } 
    finally { 
     em.close(); 
    } 

    return user; 
} 


// Inside the controller fpr my settings view (where I change the password) 
public int changePassword(String currentPassword, String newPassword, String newPasswordConfirmation) { 
    if(newPassword.isEmpty()) return 1; 
    if(!newPassword.equals(newPasswordConfirmation)) return 2;   // Incorrect confirmation 
    if(!currentPassword.equals(currentUser.getPassword())) return 3; // Given current password doesn't match the one stored in the database for this user 

    int resStatus = 0; 
    EntityManager em = factory.createEntityManager(); 
    try { 
     em.getTransaction().begin(); 
      currentUser.setPassword(newPassword); 
     em.getTransaction().commit(); // NO ERRORS at all... 
    } 
    catch(Exception e) { 
     System.out.println(e.getMessage()); 
     resStatus = 4; // Exception 
    } 
    finally { 
     em.close(); 
    } 

    return resStatus; 
} 

我也使用EntityManager.find(...)，這應該從USER表中返回同一行（和它），但結果又是同樣的嘗試 - 交易開始，完成後，實體經理關閉，但對於所謂的更改用戶表USER是相同的。

任何想法？我在另一個項目中使用了相同的例程，但是用於設置其他項目。那裏的數據庫是PostreSQL，我還沒有遇到這樣的問題。在SQLite數據庫中，我沒有收到任何錯誤，但提交失敗了。

Answer 1

我剛剛開發與休眠等，但它會是相同的，因爲兩者都實現JPA。 如果您啓動一個事務，JPA會記住您在此事務中加載的所有實體，並且如果您更改了某些內容，則會在db中看到更改（提交後）。

但是在您的事務中，JPA不會識別您的實體，因此這些更改不會持續。嘗試在事務中加載實體。像...的內容與方法

em.getTransaction().begin(); 
     em.find(User.class, currentUser.getId()); //Reload the User from db, so it is attached to the session 
     currentUser.setPassword(newPassword); 
    em.getTransaction().commit(); 

更多信息：

• https://docs.oracle.com/javaee/6/api/javax/persistence/EntityManager.html#refresh(java.lang.Object)
• https://docs.oracle.com/javaee/6/api/javax/persistence/EntityManager.html#merge(T)
• http://www.objectdb.com/java/jpa/persistence/managed