在没有创建双向关系的情况下，在JPA级别上是不可能的。您需要在用户类中指定级联类型。 用户应该是该关系的所有者，它应该提供有关如何处理相关 PasswordResetToken 的信息。

但如果你不能有双向关系，我建议你直接在模式生成SQL脚本中设置关系。

如果您通过SQL脚本创建架构而不是通过JPA自动生成（我相信所有严肃的项目必须遵循此模式），您可以在那里添加 ON DELETE CASCADE 约束。 / p>

它看起来会像这样：

  CREATE TABLE password_reset_tokens（
  - 这里的列声明
 user_id INT（11）NOT NULL，
 CONSTRAINT FK_PASSWORD_RESET_TOKEN_USER_ID 
 FOREIGN KEY（user_id）REFERENCES users（id）
 ON DELETE CASCADE 
）; 
 

这是关于如何使用数据库迁移的文档弹簧靴的工具。这里有有关如何从hibernate生成模式脚本的信息（这将简化编写自己脚本的过程）。

Maybe this is an overly simple question, but I am getting an exception when I try to delete a user entity.

The user entity:

@Entity
@Table(name = "users")
public class User 
{
    @Transient
    private static final int SALT_LENGTH = 32;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;

    @NotNull
    private String firstName;

    @NotNull
    private String lastName;

    @Column(unique = true, length = 254)
    @NotNull
    private String email;

    // BCrypt outputs 60 character results.
    @Column(length = 60)
    private String hashedPassword;

    @NotNull
    private String salt;

    private boolean enabled;

    @CreationTimestamp
    @Temporal(TemporalType.TIMESTAMP)
    @Column(updatable = false)
    private Date createdDate;

And I have an entity class which references a user with a foreign key. What I want to happen is that when the user is deleted, any PasswordResetToken objects that reference the user are also deleted. How can I do this?

@Entity
@Table(name = "password_reset_tokens")
public class PasswordResetToken 
{
    private static final int EXPIRATION_TIME = 1; // In minutes

    private static final int RESET_CODE_LENGTH = 10;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;

    private String token;

    @OneToOne(targetEntity = User.class, fetch = FetchType.EAGER)
    @JoinColumn(nullable = false, name = "userId")
    private User user;

    private Date expirationDate;

The exception I am getting boils down to Cannot delete or update a parent row: a foreign key constraint fails (`heroku_bc5bfe73a752182`.`password_reset_tokens`, CONSTRAINT `FKk3ndxg5xp6v7wd4gjyusp15gq` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`))

I'd like to avoid adding a reference to PasswordResetToken in the parent entity, becaue User shouldn't need to know anything about PasswordResetToken.

It is not possible on JPA level without creating bidirectional relation. You need to specify cascade type in User class. User should be owner of the relation and it should provide the information on how to deal with related PasswordResetToken.

But if you can't have bidirectional relation I would recommend you to setup relation directly in schema generation SQL script.

If you create your schema via SQL script and not via JPA autogeneration (I believe all serious projects must follow this pattern) you can add ON DELETE CASCADE constraint there.

It will look somehow like this:

CREATE TABLE password_reset_tokens (
  -- columns declaration here
  user_id INT(11) NOT NULL,
  CONSTRAINT FK_PASSWORD_RESET_TOKEN_USER_ID
  FOREIGN KEY (user_id) REFERENCES users (id)
    ON DELETE CASCADE
);

Here is the documentation on how to use DB migration tools with spring boot. And here is the information on how to generate schema script from hibernate (that will simplify the process of writing your own script).