盡管沒有外鍵，Hibernate 如何以一對一的關系匹配實體？

Question

我還在學習休眠 ORM。 我創建了 2 個實體：student 和 address。它們之間的關系是一對一的雙向關系。但是當我檢查數據庫時，我發現了 3 個表：Student、Address 和 hibernate_sequence（其中注冊了一個名為 next_val 的 int 屬性）。

這些是表結構： student ( STUDENT_ID , FIRST_NAME , LAST_NAME , SECTION ) address ( ADDRESS_ID , CITY , COUNTRY , STREET ) hibernate_sequence ( next_val )

盡管沒有外鍵，我想知道 hibernate 如何將學生與其地址匹配。 順便說一下，我試過 session.find(Student.class, student3.getId()) 並且我得到了那個學生的地址。

這是我的學生課：

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

@Entity
@Table(name = "STUDENT")
public class Student {

    @Id
    @GeneratedValue
    @Column(name = "STUDENT_ID")
    private long id;

    @Column(name = "FIRST_NAME")
    private String firstName;

    @Column(name = "LAST_NAME")
    private String lastName;

    @Column(name = "SECTION")
    private String section;

    @OneToOne(mappedBy="student", cascade = CascadeType.ALL)
    private Address address;

    public Student() {

    }

    public Student(String firstName, String lastName, String section) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.section = section;
    }

    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 String getSection() {
        return section;
    }

    public void setSection(String section) {
        this.section = section;
    }

    public Address getAddress() {
        return address;
    }

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

    @Override
    public String toString() {
        return "Student [id=" + id + ", firstName=" + firstName + ", lastName="
                + lastName + ", section=" + section + ", address=" + address
                + "]";
    }

}

這是我的地址代碼：

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.PrimaryKeyJoinColumn;
import javax.persistence.Table;
import org.hibernate.annotations.Parameter;
import org.hibernate.annotations.GenericGenerator;


@Entity
@Table(name = "ADDRESS")
public class Address {

    @Id
    @Column(name="ADDRESS_ID")
    @GeneratedValue(generator="gen")
    @GenericGenerator(name="gen", strategy="foreign",parameters=@Parameter(name="property", value="student"))
    private long id;

    @Column(name = "STREET")
    private String street;

    @Column(name = "CITY")
    private String city;

    @Column(name = "COUNTRY")
    private String country;

    @OneToOne
    @PrimaryKeyJoinColumn
    private Student student;

    public Address() {

    }

    public Address(String street, String city, String country) {
        this.street = street;
        this.city = city;
        this.country = country;
    }

    public long getId() {
        return id;
    }

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

    public String getStreet() {
        return street;
    }

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

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getCountry() {
        return country;
    }

    public void setCountry(String country) {
        this.country = country;
    }

    public Student getStudent() {
        return student;
    }

    public void setStudent(Student student) {
        this.student = student;
    }

    @Override
    public String toString() {
        return "Address [id=" + id + ", street=" + street + ", city=" + city
                + ", country=" + country + "]";
    }

}

Answer 1

由於它是 1 對 1 的關系，因此它使用表student的鍵值作為表address的 id 。 如果您在trace級別啟用日志記錄並（在省略大量消息后）檢查發送到數據庫的參數化查詢以及這些參數的值，您可能會看到這些詳細信息。