单向 OneToOne 映射与双向 OneToOne 映射

Question

我正在使用休眠映射，当我实现 OneToOne 双向映射时，在反面没有创建列来引用拥有方。

这些是我用过的类，

@Entity
@Table(name = "Address121_2")
public class Address {

@Id
@GeneratedValue
private int addressId;
private String city;


@OneToOne(mappedBy = "address")

private Employee employee;


public int getAddressId() {
    return addressId;
}


public void setAddressId(int addressId) {
    this.addressId = addressId;
}


public String getCity() {
    return city;
}


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


public Employee getEmployee() {
    return employee;
}


public void setEmployee(Employee employee) {
    this.employee = employee;
}


@Override
public String toString() {
    return "Address [addressId=" + addressId + ", city=" + city + ", employee=" + employee + "]";
}

}

另一个，

@Entity
@Table(name="emp121_2")
public class Employee {

@Id
@GeneratedValue
private int employeeId;  
private String name;
private String email; 

@OneToOne
@JoinColumn(name="a_id")
private Address address;


public int getEmployeeId() {
    return employeeId;
}
public void setEmployeeId(int employeeId) {
    this.employeeId = employeeId;
}
public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}
public String getEmail() {
    return email;
}
public void setEmail(String email) {
    this.email = email;
}
public Address getAddress() {
    return address;
}
public void setAddress(Address address) {
    this.address = address;
}
@Override
public String toString() {
    return "Employee [employeeId=" + employeeId + ", name=" + name + ", email=" + email + ", address=" + address
            + "]";
}

}

所以如果没有从反面到拥有面的引用，双向映射有什么用？

Answer 1

主要区别在于双向将为您提供两个方向的导航访问。这意味着您无需查询即可获得关系的另一端。

它还允许级联选项（在 @OneToMany 关于性能方面要小心）。

单向或双向在数据库中没有区别。

单向 OneToOne 映射与双向 OneToOne 映射

Uni-directinal OneToOne mapping vs Bi-directinal OneToOne mapping

java

hibernate

hibernate-mapping