Question

我创建了三个类 - User，UserSubscription和Subscription。我希望UserSubscription表中的用户应该由User表中的用户引用。那么，如何使用mappedBy？课程如下：

用户：

    package com.model;

    import java.util.HashSet;
    import java.util.Set;

    import javax.persistence.CascadeType;
    import javax.persistence.Column;
    import javax.persistence.Entity;
    import javax.persistence.FetchType;
    import javax.persistence.GeneratedValue;
    import javax.persistence.Id;
    import javax.persistence.JoinColumn;
    import javax.persistence.JoinTable;
    import javax.persistence.ManyToMany;
    import javax.persistence.OneToOne;

    @Entity
    public class User {


    private int userId;
    private String password;
    private String contact;  
    private String firstName;
    private String lastName;
    private String gender;
    private String address;
    private int age;
    private String email;
    private String countBooks;


    private Set<Language> languages = new HashSet<Language>(0);
    private Set<Book> favorites = new HashSet<Book>(0);


    @Id
    @GeneratedValue
    @Column(name="User_Id")
    public int getUserId() {
        return userId;
    }

    public void setUserId(int userId) {
        this.userId = userId;
    }

    @Column(name="Password")
    public String getPassword() {
        return password;
    }

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


    @Column(name="Contact")
    public String getContact() {
        return contact;
    }

    public void setContact(String contact) {
        this.contact = contact;
    }


    @Column(name="First_Name")
    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }


    @Column(name="Last_Name")
    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }


    @Column(name="Gender")
    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }


    @Column(name="Address")
    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }


    @Column(name="Age")
    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }


    @Column(name="Email")
    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }


    @Column(name="Count_Books")
    public String getCountBooks() {
        return countBooks;
    }

    public void setCountBooks(String countBooks) {
        this.countBooks = countBooks;
    }

    @ManyToMany(cascade=CascadeType.ALL)
    @JoinTable(name="User_Language", joinColumns = { 
            @JoinColumn(name = "User_Id", nullable = false, updatable = false) }, 
            inverseJoinColumns = { @JoinColumn(name = "Language_Id", 
                    nullable = false, updatable = false) })
    public Set<Language> getLanguages() {
        return languages;
    }

    public void setLanguages(Set<Language> languages) {
        this.languages = languages;
    }

    @ManyToMany
    @JoinTable(name="User_Favorite", joinColumns = { 
            @JoinColumn(name = "User_Id", nullable = false, updatable = false) }, 
            inverseJoinColumns = { @JoinColumn(name = "Book_Id", 
                    nullable = false, updatable = false) })
    public Set<Book> getFavorites() {
        return favorites;
    }

    public void setFavorites(Set<Book> favorites) {
        this.favorites = favorites;
    }   

}

UserSubscription：

package com.model;

import java.sql.Date;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToOne;

@Entity
public class UserSubscription {

    private int userSubscriptionId;
    private Subscription subscription;
    private User user;
    private Date subscriptionStartDate;
    private Date subscriptionEndDate;
    private int status;


    @Id
    @GeneratedValue
    @Column(name="User_Subscription_Id")
    public int getUserSubscriptionId() {
        return userSubscriptionId;
    }
    public void setUserSubscriptionId(int userSubscriptionId) {
        this.userSubscriptionId = userSubscriptionId;
    }

    @Column(name="Subscription_Id")
    public Subscription getSubscription() {
        return subscription;
    }
    public void setSubscription(Subscription subscription) {
        this.subscription = subscription;
    }
    @OneToOne(mappedBy="userId")
    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
    }

    @Column(name="Subscription_Start_Date")
    public Date getSubscriptionStartDate() {
        return subscriptionStartDate;
    }
    public void setSubscriptionStartDate(Date subscriptionStartDate) {
        this.subscriptionStartDate = subscriptionStartDate;
    }

    @Column(name="Subscription_End_Date")
    public Date getSubscriptionEndDate() {
        return subscriptionEndDate;
    }
    public void setSubscriptionEndDate(Date subscriptionEndDate) {
        this.subscriptionEndDate = subscriptionEndDate;
    }

    @Column(name="Status")
    public int getStatus() {
        return status;
    }
    public void setStatus(int status) {
        this.status = status;
    }





}

package com.model;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

@Entity
public class Subscription {


    private int subscriptionId;
    private String name;
    private int period;
    private float fees;
    private int noOfBooks;
    private int Status;

    @Id
    @GeneratedValue
    public int getSubscriptionId() {
        return subscriptionId;
    }
    public void setSubscriptionId(int subscriptionId) {
        this.subscriptionId = subscriptionId;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getPeriod() {
        return period;
    }
    public void setPeriod(int period) {
        this.period = period;
    }
    public float getFees() {
        return fees;
    }
    public void setFees(float fees) {
        this.fees = fees;
    }
    public int getNoOfBooks() {
        return noOfBooks;
    }
    public void setNoOfBooks(int noOfBooks) {
        this.noOfBooks = noOfBooks;
    }
    public int getStatus() {
        return Status;
    }
    public void setStatus(int status) {
        Status = status;
    }



}

执行时出现异常：

Exception in thread "main" org.hibernate.AnnotationException: Referenced property not a (One|Many)ToOne: com.model.User.userId in mappedBy of com.model.UserSubscription.user
    at org.hibernate.cfg.OneToOneSecondPass.doSecondPass(OneToOneSecondPass.java:248)
    at org.hibernate.cfg.Configuration.originalSecondPassCompile(Configuration.java:1695)
    at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1424)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1844)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1928)
    at com.impetus.model.Check.main(Check.java:92)

Answer 1

在您的代码中，user-user_subscription看起来是单向的。 'mappedby'应该用于双向关系。

您可以在用户实体中使用以下代码，使其与user_subscription成双向。

private UserSubscription userSubscription; 
@OneToOne
    public User getUserSubscription() {
        return userSubscription;
    }

或者从user_subscription中删除mappedby并使其成为单向的。

Answer 2

你的User类中应该有UserSubscription memeber和corrosponding gettes和setter，如下所示：

private Set<Company> userSubscriptions = new HashSet<Company>(0);

@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "user")
public Set<UserSubscription> getUserSubscriptions() {

    return this.userSubscriptions ;
}

public void setUserSubscriptions(Set<UserSubscription> userSubscriptions ) {

    this.userSubscriptions = userSubscriptions ;
}

以及在UserSubscription实体类中将用户对象作为memeber的方式相同。

私人用户;

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "USER_ID", nullable = false)
public User getUser() {

    return this.user;

}

public void setUser(User user) {

    this.user = user;
}

Answer 3

你做错了

class User {
    UserSubscription userSubscription ;

    @OneToOne
    public  UserSubscription getUserSubscription(){
        return userSubscription ;
    }
    public  void setUserSubscription(UserSubscription  userSubscription ){
        this.userSubscription = userSubscription ;
    }
}

class UserSubscription {
    @OneToOne(mappedBy="userSubscription")
    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
    }
}

Answer 4

似乎您不确定使用了什么是mappedBy或意味着什么。数据库关系是单方面的;一个表将具有目标表的外键引用。在JPA中，您可以将此关系映射为OneToOne，并指定要与@JoinColumn批注一起使用的外键：

@OneToOne(mappedBy="userId")
@JoinColumn(name = "USER_ID")
public User getUser() {
    return user;
}

Join列定义是可选的，如果不使用，JPA将默认使用属性名称＆＃34; _＆＃34;并且目标实体的ID名称前置，因此＆＃34; USER_ID＆＃34;在这种情况下无论如何。

回到数据库，因为源表引用了目标表，这形成了另一个隐式关系（目标表的ID可以用来查找另一个表的外键）。在JPA中，这可以再次映射为OneToOne或OneToMany，具体取决于基数。如果它是OneToOne，则指定此关系不通过将其标记为mappedBy与其他关系来定义外键：

@OneToOne(mappedBy="user")
public UserSubscription getUserSubscription() {
    return userSubscription;
}

但用户更有可能拥有多个userSubscriptions：

@OneToMany(mappedBy="user")
public Collection<UserSubscription> getUserSubscriptions () {
    return userSubscription ;
}

在这两种情况下，您都使用mappedBy来表示有一个＆＃39;用户＆＃39;目标实体中的属性，用于定义与此实体的关系，并控制数据库中的外键设置。

您还需要更改定义UserSubscription-＆gt;订阅关系的方式，因为您已经定义了@Column似乎是一种关系。应该是

@OneToOne
@JoinColumn(name="Subscription_Id")
public Subscription getSubscription() {
    return subscription;
}

在OneToOne映射中映射MappedBy

4 个答案: