java - 如何正确地将表单绑定(bind)到@ManyToOne结构并保存到数据库。 Spring MVC、 hibernate

Question

我是一名 Java 开发新手，现在使用 Spring-Hibernate 开发用户管理应用程序。我有两个实体用户和电子邮件。用户实体有一个电子邮件字段，它被映射到电子邮件实体作为@ManyToOne。任何电子邮件都可以由多个用户使用。

当我在数据库中为每个新用户保存一个新用户时，我会收到一个新行电子邮件，即使电子邮件表中已存在相同的记录。如何正确进行保存操作以避免Email表中相同记录重复？

User.java

@Entity
@Table(name = "USER")
public class User implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name="ID")
    private Long id;
    @Column(name = "name")
    private String name;
    @ManyToOne
    @JoinColumn(name = "email_id")
    private Email email;
    public User(){
    }
    public Email getEmail() {
        return email;
    }
    public void setEmail(Email email) {
        this.email = email;
    }
...
}

Email.java

@Entity
@Table(name = "EMAIL")
public class Email implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name="ID")
    private Long id;
    @Column(name = "emailaddress")
    private String emailaddress;
    @OneToMany (mappedBy = "email", targetEntity=User.class)
    private Set<User> user= new HashSet<User>();

    public Email() {
    }
    public Email(String emailaddress) {
        this.emailaddress = emailaddress;
    }

    public String getEmailaddress() {
        return emailaddress;
    }
    public void setEmailaddress(String emailaddress) {
        this.emailaddress = emailaddress;
    }
...
}

Controller.java

@Transactional
@RequestMapping(value = "/adduser", method = RequestMethod.POST)
    public String saveOrder(@ModelAttribute("user") User user, BindingResult result, @RequestParam String action){
    emailDAO.create(user.getEmail());
    userDAO.create(user);
    return "index";
...
}

EmailDAO.java

@Transactional
@Repository
public class EmailDAO{
    @Autowired
    private SessionFactory sessionFactory;
    public Email create(Email email) {
        sessionFactory.getCurrentSession().save(email);
        return email;
    }
}

UserDAO.java

@Transactional
@Repository
public class UserDAO{
    @Autowired
    private SessionFactory sessionFactory;

    public User create(User user) {
        sessionFactory.getCurrentSession().save(user);
        return user;
    }
}

webform.jsp

<form:form action="${formUrl}" method="post" modelAttribute="user">
    <form:label path="name" for="appname">username</form:label>
    <form:input path="name" id= "appname" cssClass="form-control"/>

    <form:label path="email.emailaddress" for="appemail">Email</form:label>
    <form:input path="email.emailaddress" id= "appemail"/>
    <button type="submit" name="action" value="Add">Save</button>
</form:form>

数据库图表

数据库记录示例

Answer 1

那是因为您继续将电子邮件保存为新记录

@Transactional
@RequestMapping(value = "/adduser", method = RequestMethod.POST)
    public String saveOrder(@ModelAttribute("user") User user, BindingResult result, @RequestParam String action){
    emailDAO.create(user.getEmail()); // Inserting Email as New Record
    userDAO.create(user);
    return "index";
...
}

并且您在电子邮件实体上没有unique=true

@Column(name = "emailaddress", unique = true)
private String emailaddress;

理想情况下您应该拥有它，这样即使不小心也不会插入重复的电子邮件。

您需要修改EmailDAO

@Transactional
@Repository
public class EmailDAO{
    @Autowired
    private SessionFactory sessionFactory;

    public Email create(Email email) {
        sessionFactory.getCurrentSession().save(email);
        return email;
    }

    public Email getEmail(String inputEmail) {
        Email email = null;
        Query query = sessionFactory.getCurrentSession().createQuery("FROM Email e WHERE e.emailaddress = :email");
        query.setString("email", inputEmail);
        List emails = query.list();
        if(emails != null && emails.size() > 0) {
            email = (Email)emails.get(0);
        } else {
            email = new Email();
            email.setEmailAddress(inputEmail);
        }
        return email;
    }
}

然后你获取电子邮件

@Transactional
@RequestMapping(value = "/adduser", method = RequestMethod.POST)
    public String saveOrder(@ModelAttribute("user") User user, BindingResult result, @RequestParam String action){
    user.setEmail(emailDAO.getEmail(user.getEmail().getEmailAddress())); // Inserting Email as New Record
    userDAO.create(user);
    return "index";
...
}