什么是@JoinColumn以及如何在Hibernate中使用

  • Z时代
  • 2024-01-10
  • 分类：问答

我已经阅读了很多有关@JoinColumn的内容，但是我仍然不明白它的含义。

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 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;
``
我对Vehicle类的部分感到困惑，两者之间的关系是什么

Vehicle Class ---- Entity

@JoinColumn(name=”patient_id”) ---- annotation

private Patient patient ----field

```

会说吗？该车辆实体有一个外键到患者实体命名patient_id。将Patient_id作为列添加到“车辆实体”表中

回答：

通过联接表的单向关联

@Entity
class Patient {
    @OneToMany
    private Collection<Vehicle> vehicles = new ArrayList<Vehicle>();
}
@Entity
class Vehicle {
}

通过联接表的双向关联

@Entity
class Patient {
    @OneToMany
    private Collection<Vehicle> vehicles = new ArrayList<Vehicle>();
}
@Entity
class Vehicle {
    @ManyToOne(fetch = FetchType.LAZY)
    private Patient patient;
}

通过外键进行单向关联

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

通过外键进行双向关联

@Entity
class Patient {
    @OneToMany(mappedBy = "patient")
    private Collection<Vehicle> vehicles = new ArrayList<Vehicle>();
}
@Entity
class Vehicle {
    @ManyToOne(fetch = FetchType.LAZY)
    private Patient patient;
}

通过外键与外列名称说明的双向关联

@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;
}

这是使用的基本起点@JoinColumn。

要验证的外键（patient_id在Vehicle表）中可以使用患者台真正映射@JoinColumn(nullable = false)

@Entity
class Vehicle {
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name="patient_id", nullable = false)
    private Patient patient
}

以上是 什么是@JoinColumn以及如何在Hibernate中使用 的全部内容， 来源链接： utcz.com/qa/432711.html

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