我正在使用Spring开发一个Java程序，该程序使用JPA与数据库通信。在我的应用程序中，我有多个类，但我遇到了User和Equipment类的问题。每个用户都拥有设备，每个设备都有一个状态。（已分配，未分配，或正在维修中）。我的目标是在删除用户时自动将关联设备的状态从已分配更新为未分配。如何实现？请参阅下面的代码片段以供参考：

package se.what.inventorymanager;
import jakarta.persistence.*;
import java.util.Date;
@Entity
@Table(name="equipment")
public class Equipment {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    @Column(name="equipment_name")
    private String name;
    @Column(name="purchase_date")
    private Date purchaseDate;
    @Column(name="purchase_price")
    private double purchasePrice;
    @Enumerated(EnumType.STRING)
    private EquipmentState state;
    @Enumerated(EnumType.STRING)
    private EquipmentType type;
    @OneToOne(mappedBy = "equipment")
    private EquipmentSupport equipmentSupport;
    @ManyToOne
    @JoinColumn(name = "purchased_by", referencedColumnName = "id")
    private User user;
    public Equipment() {}
    public Equipment(String name, Date purchaseDate, double purchasePrice, EquipmentState state,
                     EquipmentType type, User user) {
        this.name = name;
        this.purchaseDate = purchaseDate;
        this.purchasePrice = purchasePrice;
        this.state = state;
        this.type = type;
        this.user = user;
    }
    public int getId() {
        return id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Date getPurchaseDate() {
        return purchaseDate;
    }
    public void setPurchaseDate(Date purchaseDate) {
        this.purchaseDate = purchaseDate;
    }
    public double getPurchasePrice() {
        return purchasePrice;
    }
    public void setPurchasePrice(double purchasePrice) {
        this.purchasePrice = purchasePrice;
    }
    public EquipmentState getState() {
        return state;
    }
    public void setState(EquipmentState state) {
        this.state = state;
    }
    public EquipmentType getType() {
        return type;
    }
    public void setType(EquipmentType type) {
        this.type = type;
    }
    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
    }
    @Override
    public String toString() {
        return "Equipment{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", purchaseDate=" + purchaseDate +
                ", purchasePrice=" + purchasePrice +
                ", state=" + state +
                ", type=" + type +
                ", equipmentSupport=" + equipmentSupport +
                ", user=" + user.getName() +
                '}';
    }
    @PreUpdate
    @PrePersist
    public void updateEquipmentState() {
        if (user == null) {
            state = EquipmentState.unassigned;
        }
    }
}
package se.what.inventorymanager;
import jakarta.persistence.*;
@Entity
@Table(name = "user")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    private String name;
    private String department;
    private String email;
    private String telephone;
    private String username;
    private String password;
    @Column(name = "role")
    @Enumerated(EnumType.STRING)
    private RoleType role;
    public User(String name, String department, String email, String telephone, String username, String password, RoleType role) {
        this.name = name;
        this.department = department;
        this.email = email;
        this.telephone = telephone;
        this.username = username;
        this.password = password;
        this.role = role;
    }
    public User() {
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getDepartment() {
        return department;
    }
    public void setDepartment(String department) {
        this.department = department;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
    public String getTelephone() {
        return telephone;
    }
    public void setTelephone(String telephone) {
        this.telephone = telephone;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public RoleType getRole() {
        return role;
    }
    public void setRole(RoleType role) {
        this.role = role;
    }
    @Override
    public String toString() {
        return "\nUser id: " + id + " Name: " + name  + " Department: " + department + " Email: " + email + " Telephone: "
                + telephone + " Username: " + username + " Password: " + password + " Role: " + role;
    }
}
;

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