JavaEE JPA synchronise object with database - jpa

Question

I've got a User class and an Email class.
I used the #OneToMany annotatioin to describe a realationship that one user can have many emails and one email is assigned to one user.
Now the problem is: when creating a user and an email and assigning the email to the user, I try to find a way that the Set of emails is getting initialized by JPA. Usually this works fine when I am doing em.find(User.class, "test");
This only does not work when I'm creating a user. The emails attribute is always of size 0 or even null. But when I create a user, then redeploy my application and then execute em.find(User.class, "test"), the emails attribute is set correctly of size 1 and I can access it.
#Entity
public class User implements Serializable {
private String username;
private String password;
private Set<Email> emails;
#OneToMany(mappedBy = "user", fetch = FetchType.EAGER)
public Set<Email> getEmails() {
return emails;
}
public void setEmails(Set<Email> emails) {
this.emails = emails;
}
#Id
#Column(name = "Username")
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
#Basic
#Column(name = "Password")
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
-
#Entity
public class Email implements Serializable {
private int id;
private String email;
private User user;
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "Id")
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
#ManyToOne
#JoinColumn(name = "user")
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
#Basic
#Column(name = "Email")
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
-
User user = new User();
user.setUsername("test");
user.setPassword("asdf");
em.persist(user);
Email e = new Email();
e.setEmail("test#test.com");
e.setUser(user);
em.persist(e);
return user;
after executing these statements, the user attribute emails is null (obviously). But strangely when I do em.find(User.class, "test"); in another method, the emails attribute is of size 0, even though the records are correctly inserted to the database.
When I now redeploy my application and call em.find(User.class, "test"); again, the emails attribute is of size 1.
I've already tried to call em.merge(); or em.refresh(); which did not work.
I am using glassfish 4.1.1. As transaction-type I use JTA and eclipselink for the JPA implementation

Answer 1

You need to add the email to the User as well and merge the user if you are doing it in two steps, or (you may need cascade=CascadeType.ALL) just put it in the User to begin with and persist the User if you are doing it in one step.
User user = new User();
Set<Email> emails = new HashSet<Email>();
user.setEmails(emails);
user.setUsername("test");
user.setPassword("asdf");
Email e = new Email();
e.setEmail("test#test.com");
e.setUser(user);
emails.add(e);
em.persist(user);
return user;

Answer 2

You need to set both sides of any bidirectional relationship, JPA will not do it for you. If you do not, the unset side will not reflect what is in the database until it is reloaded/refreshed from the database. You can force the refresh using em.refresh(user), but it is usually better to avoid the database hit and just add the email to the user's list of emails.