问题描述
我已经阅读了很多关于@JoinColumn 的文章，但我仍然不明白它背后的想法.
I have been reading a lot about @JoinColumn but I still don't get the idea behind it.
病床
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 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));
患者分类
@OneToMany(mappedBy = "patient")
private Collection<Vehicle> patientVehicles = new ArrayList<Vehicle>();
车辆类别
@ManyToOne
@JoinColumn(name="patient_id")
private Patient patient;
我很困惑Vehicle类是如何部分的，它们之间的关系是什么
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
有没有说；车辆实体有一个外键到患者实体，名为patient_id.将 patient_id 添加为车辆实体表
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
JoinColumn 的名称参数是否应该始终是外键或主键?
Do the name parameter of the JoinColumn should always be a Foreign Key or Primary Key?
我一直在读这个，但我仍然很困惑.JPA JoinColumn 与 mappingBy
I have been reading this but I'm still confuse.JPA JoinColumn vs mappedBy
推荐答案
通过连接表的单向关联
@Entity
class Patient {
@OneToMany
private Collection<Vehicle> vehicles = new ArrayList<Vehicle>();
}
@Entity
class Vehicle {
}
通过连接表的双向关联
@Entity
class Patient {
@OneToMany
private Collection<Vehicle> vehicles = new ArrayList<Vehicle>();
}
@Entity
class Vehicle {
@ManyToOne(fetch = FetchType.LAZY)
private Patient patient;
}
通过外键的单向关联
@Entity
class Patient {
@OneToMany
@JoinColumn
private Collection<Vehicle> vehicles = new ArrayList<Vehicle>();
}
@Entity
class Vehicle {
}
通过外键的双向关联
@Entity
class Patient {
@OneToMany(mappedBy = "patient")
private Collection<Vehicle> vehicles = new ArrayList<Vehicle>();
}
@Entity
class Vehicle {
@ManyToOne(fetch = FetchType.LAZY)
private Patient patient;
}
通过具有外列名称规范的外键的双向关联
@Entity
class Patient {
@OneToMany(mappedBy = "patient")
private Collection<Vehicle> vehicles = new ArrayList<Vehicle>();
}
@Entity
class Vehicle {
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name="patient_id")
private Patient patient;
}
这是使用@JoinColumn的基本起点.
要验证外键(Vehicle 表中的patient_id)是否真的映射到了患者表中，您可以使用 @JoinColumn(nullable = false)
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 {
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name="patient_id", nullable = false)
private Patient patient
}
这篇关于什么是@JoinColumn 以及它在 Hibernate 中的使用方式的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！