Java 休眠一对一关系和外键问题

我有一个奇怪的问题，我找不到。我有两个类，Employee和Address，用于创建具有一对一关系的两个表。 当我检查一个操作的结果时，我看到记录已经添加，但没有外键到表Employee example中的地址：

1   John      Smith     12333    null

其中null是地址\ u ID。 当我检查地址表时，我看到记录被添加了，但id的开始编号是2

2   New York    st. Aperman 234 12  03999

雇员阶级

@Entity
public class Employee {
@Id
@GeneratedValue
private long id;

private String firstName;
private String lastName;
private double salary;

@OneToOne 
@JoinColumn(name = "address_ID") 
private Address address;

public long getId() {
    return id;
}

public void setId(long id) {
    this.id = id;
}

public String getFirstName() {
    return firstName;
}

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

public String getLastName() {
    return lastName;
}

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

public double getSalary() {
    return salary;
}

public void setSalary(double salary) {
    this.salary = salary;
}

public Address getAddress() {
    return address;
}

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

}

地址类

@Entity
public class Address {
@Id
@GeneratedValue
private long id;

public String locality;
public String zipCode;
public String street;
public int streetNumber;


public long getId() {
    return id;
}

public void setId(long id) {
    this.id = id;
}

public String getLocality() {
    return locality;
}

public void setLocality(String locality) {
    this.locality = locality;
}

public String getZipCode() {
    return zipCode;
}

public void setZipCode(String zipCode) {
    this.zipCode = zipCode;
}

public String getStreet() {
    return street;
}

public void setStreet(String street) {
    this.street = street;
}

public int getStreetNumber() {
    return streetNumber;
}

public void setStreetNumber(int streetNumber) {
    this.streetNumber = streetNumber;
}

}

主类

public class Main {

public static void main(String[] args) {
    EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("tutorialdb");
    EntityManager entityManager = entityManagerFactory.createEntityManager();

    Employee employee = new Employee();
    Address adres = new Address();      
            employee.setFirstName("John");
            employee.setLastName("Smith");
            employee.setSalary(12333.0);
            adres.setLocality("New York");
            adres.setZipCode("03999");
            adres.setStreet("st. Aperman 234");
            adres.setStreetNumber(12);

            entityManager.getTransaction().begin();
            entityManager.persist(employee);
            entityManager.persist(adres);
            entityManager.getTransaction().commit();


    entityManager.close();
    entityManagerFactory.close();

}

}

persistence.xml

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
version="2.0">
<persistence-unit name="tutorialdb"
    transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <properties>
      <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
     <property name="javax.persistence.jdbc.user" value="user"/>
     <property name="javax.persistence.jdbc.password" value="password"/>
     <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/tutorial"/>
     <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL8Dialect"/>
     <property name="hibernate.hbm2ddl.auto" value="create"/>
    </properties>
</persistence-unit>

org.hibernate.ejb.HibernatePersistence

---

您需要在

员工

中设置

地址

引用，然后才能持久化

地址地址=新地址（）；
...
雇员地址（adres）；

---

Employee表中的外键为

null

，因为在

Employee

中没有设置地址，现在确定Employee中的外键为add，但在表address中，当我向空表添加记录时，其id总是以2开头。您知道为什么吗？当您尝试持久化时，会为该事务创建一个id，并且该id不能重复使用。这意味着，如果事务失败，该ID将被忽略。