什么是@JoinColumn，以及它如何在Hibernate中使用 [英] what is @JoinColumn and how it is used in Hibernate

问题描述

患者表

  CREATE TABLE patient（
 patient_id BIGINT NOT NULL，
 first_name VARCHAR（255）NOT NULL，
 last_name VARCHAR（255）NOT NULL，
 PRIMARY KEY（patient_id））; 
  

车辆表

  CREATE TABLE车辆（
 patient_id BIGINT不为NULL，
 vehicle_id BIGINT不为NULL，
 vehicle_manufacturer VARCHAR（255），
 PRIMARY KEY（vehicle_id），
 CONSTRAINT patienthasmanyvehicle FOREIGN KEY（patient_id）参考患者（patient_id））; 
  

病人分类

  @OneToMany（mappedBy =patient）
 private Collection< Vehicle> patientVehicles = new ArrayList< Vehicle>（）; 
  

车辆级别

  @ManyToOne 
 @JoinColumn（name =patient_id）
私人患者; 
  

我很困惑Vehicle类的部分，

 车辆类别----实体
 @JoinColumn（name =patient_id）----注释
私人患者患者----现场
  

是否说; 车辆实体具有名为 patient_id 的外键至患者实体。
将 patient_id 添加为车辆实体表中的一列

JoinColumn应始终是一个外键或主键？

我一直在阅读这篇文章，但我仍然很迷惑。
JPA JoinColumn vs mappedBy

解决方案

通过连接表进行关联

  @Entity 
 class病人{
 
 @OneToMany 
私人收藏< Vehicle> patientVehicles = new ArrayList< Vehicle>（）; 
 
} 
 
 @ Entity 
 class Vehicle {
 
} 
  

$ b

通过外键进行单向关联

  @Entity 
 class Patient {
 
 @OneToMany 
 @JoinColumn（name =patient_id）
 private Collection< Vehicle> patientVehicles = new ArrayList< Vehicle>（）; 
 
} 
 
 @ Entity 
 class Vehicle {
 
} 
  

$ b

通过外键进行双向关联

  @Entity 
类Patient {
 
 @OneToMany（mappedBy =patient）
 private Collection< Vehicle> patientVehicles = new ArrayList< Vehicle>（）; 
 
} 
 
 @ Entity 
 class车辆{
 
 @JoinColumn（name =patient_id）
私人患者患者
 
 
 
 
 $ b 
这是使用<$ c $的基本出发点c> @JoinColumn 。
 
 
 
验证外键（ patient_id  车辆表）确实映射到您可以使用的患者表中 @JoinColumn（nullable = false） 
  @Entity 
 class Vehicle {
 
 @JoinColumn（name =patient_id，nullable = false） 
私人病人
 
} 
  
 
I have been reading a lot about @JoinColumn but I still don't get the idea behind it.

Patient Table
CREATE TABLE patient (
patient_id BIGINT NOT NULL,
first_name VARCHAR(255) NOT NULL,
last_name VARCHAR(255) NOT NULL,
PRIMARY KEY(patient_id));
Vehicle Table
CREATE TABLE vehicles (
patient_id BIGINT NOT NULL,
vehicle_id BIGINT NOT NULL,
vehicle_manufacturer VARCHAR(255),
PRIMARY KEY (vehicle_id),
CONSTRAINT patienthasmanyvehicle FOREIGN KEY(patient_id) REFERENCES patient(patient_id));
Patient Class
@OneToMany(mappedBy = "patient")
    private Collection<Vehicle> patientVehicles = new ArrayList<Vehicle>();
Vehicle Class
@ManyToOne
@JoinColumn(name="patient_id")
private Patient patient;
I'm confused on how the Vehicle class part, what is the relationship between 
Vehicle Class ---- Entity
@JoinColumn(name="patient_id") ---- annotation
private Patient patient ----field
Does it say; The Vehicle Entity has a Foreign Key to Patient entity named patient_id. 
Add the patient_id as a column in the Vehicle Entity table

Do the name parameter of the JoinColumn should always be a Foreign Key or Primary Key?

I have been reading this but I'm still confuse.
JPA JoinColumn vs mappedBy
解决方案
An association via a join table
@Entity
class Patient {

    @OneToMany
    private Collection<Vehicle> patientVehicles = new ArrayList<Vehicle>();

}

@Entity
class Vehicle {

}
A unidirectional association via a foreign key
@Entity
class Patient {

    @OneToMany
    @JoinColumn(name = "patient_id")
    private Collection<Vehicle> patientVehicles = new ArrayList<Vehicle>();

}

@Entity
class Vehicle {

}
A bidirectional association via a foreign key
@Entity
class Patient {

    @OneToMany(mappedBy = "patient")
    private Collection<Vehicle> patientVehicles = new ArrayList<Vehicle>();

}

@Entity
class Vehicle {

    @JoinColumn(name="patient_id")
    private Patient patient

}
This is the basic starting point of using @JoinColumn.

To verify that the foreign key(patient_id in the Vehicle table) is really mapped in the patients table you can use @JoinColumn(nullable = false)
@Entity
class Vehicle {

    @JoinColumn(name="patient_id", nullable = false)
    private Patient patient

}


                        
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