JPA 2 - 如何使用 Spring Data JPA 构建具有主键同时也是外键的实体？

Question

给定下表：

Car
int id PK
int modelId FK

CarDetails
int carId PK, FK to Car.id
varchar(50) description

如何表示 CarDetails 的 @Id 也是 Car 的外键？

我试过：

@Entity
public class Car {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @ManyToOne
    @JoinColumn(name = "modelId", nullable = false)
    private Model model;

    //setters & getters
}

@Entity
public class CarDetails {

    @Id
    @OneToOne
    @JoinColumn(name = "carId", nullable = false)
    private Car car;

    private String description;

    //setters & getters
}

但是，我得到了错误

org.hibernate.MappingException: Composite-id class must implement Serializable: com.example.CarDetails

实施 Serializable 后，我得到 This class [class com.example.CarDetails] does not define an IdClass。但是在将 @IdClass(Car.class) 添加到 CarDetails class 后我仍然得到错误。

更新

IdClass 错误源自 Spring： Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'carDetailsRepository': Invocation of init method failed; nested exception is java.lang.IllegalArgumentException: This class [class com.example.CarDetails] does not define an IdClass

这是 CarDetailsRepository：

public interface CarDetailsRepository extends JpaRepository<CarDetails, Car> {

}

以下是我的 gradle 构建文件的相关部分：

plugins {
    id 'java'
    id 'eclipse'
    id 'maven-publish'
    id 'io.spring.dependency-management' version '1.0.3.RELEASE'
}

repositories {
    mavenCentral()
    mavenLocal()
}


dependencies {

    pmd group: 'org.hibernate', name: 'hibernate-tools', version: '5.2.3.Final'
    pmd group: 'org.hibernate', name: 'hibernate-core', version: '5.2.10.Final'
    pmd group: 'org.hibernate.common', name: 'hibernate-commons-annotations', version: '5.0.1.Final'

    compile('org.springframework.boot:spring-boot-starter')
    compile('org.springframework.boot:spring-boot-starter-data-jpa')
    compile('org.hibernate:hibernate-validator:5.2.4.Final')
    compile('org.hibernate:hibernate-envers:5.2.10.Final')
    compile('org.hibernate:hibernate-core:5.2.10.Final')
    compile('org.hibernate.common:hibernate-commons-annotations:5.0.1.Final')
    runtime('net.sourceforge.jtds:jtds:1.3.1')
    runtime('com.microsoft.sqlserver:sqljdbc:4.2')
    runtime('javax.el:javax.el-api:2.2.4')
    testCompile('org.springframework.boot:spring-boot-starter-test')
}

dependencyManagement {
    imports { mavenBom('org.springframework.boot:spring-boot-dependencies:1.5.4.RELEASE') }
}

Answer 1

可能最好的方法是在您的 CarDetails 实体中引用 carId 两次——一次用于 @Id，一次用于外键引用。您必须使用 insertable=false 和 updatable=false 声明这些引用之一，这样 JPA 就不会在尝试在两个位置管理同一列时感到困惑：

@Entity
public class CarDetails {

    @Id
    @Column(name = "carId", insertable = false, updatable = false)
    private int carId; // don't bother with getter/setter since the `car` reference handles everything

    @OneToOne
    @JoinColumn(name = "carId", nullable = false)
    private Car car;

    private String description;

    //setters & getters
}

它看起来很奇怪，但它会起作用，而且它实际上是（最）首选的方法。

Answer 2

您可以尝试这样映射 CarDetails：

@Entity
public class CarDetails {

    @Id
    private int id;

    @MapsId
    @OneToOne
    @JoinColumn(name = "carId", nullable = false)
    private Car car;

    private String description;

    //setters & getters
}

注意 @MapsId 注释。

JPA 2 - 如何使用 Spring Data JPA 构建具有主键同时也是外键的实体？

JPA 2 - How to build entity that has Primary key that is also a foreign key using Spring Data JPA?

java

hibernate

jpa

jpa-2.0

spring-data-jpa