违反参照完整性约束：删除 Hibernate 中的实体时（memory DBMS 中的 H2）

Question

I am building my first Spring Boot application. I use Hibernate and an H2 in-memory DBMS.

What I am trying to build is a REST API that represents a number of App-Stores. I have an entity called App and another called Store. A store can contain many apps and each app can be contained in more than one store. Apps however, do not know in which stores they are contained. I want to be able to delete apps and stores independently of each other. Just because a store was deleted does not mean the apps therein should be deleted too and vice versa. Apps can exist without being in a store and stores without apps are fine too.

Here is the code for my entities, LpApp is the implementation for an App and LpTemplate is the implementation of a Store:

@Entity
public class LpApp {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(nullable = false, updatable = false)
    private Long id;

    @NotBlank(message = "An app needs a non-empty name")
    @Column(nullable = false, updatable = false, unique = true)
    private String appName;

    // ... constructors, getters, setters, no further annotations
}

@Entity
public class LpTemplate {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(nullable = false, updatable = false)
    private Long id;

    @ManyToMany(fetch=FetchType.EAGER)
    @JoinTable(name = "template_apps",
        inverseJoinColumns = { @JoinColumn(name = "app_id") },
        joinColumns = { @JoinColumn(name = "template_id") })
    private Set<LpApp> apps = new HashSet<>();

    // ... constructors, getters, setters, no further annotations

}

This works well until I attempt to delete an App or Store from my DBMS. At this point I get an org.h2.jdbc.JdbcSQLIntegrityConstraintViolationException.

The exception I get is the following (I trimmed the call stack for brevity):

org.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint ["APP_ID: PUBLIC.TEMPLATE_APPS FOREIGN KEY(APP_ID) REFERENCES PUBLIC.LP_APP(ID) (3)"; SQL statement:
delete from lp_app where id=? [23503-199]]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement
...
Caused by: org.hibernate.exception.ConstraintViolationException: could not execute statement
...
Caused by: org.h2.jdbc.JdbcSQLIntegrityConstraintViolationException: Referential integrity constraint violation: "APP_ID: PUBLIC.TEMPLATE_APPS FOREIGN KEY(APP_ID) REFERENCES PUBLIC.LP_APP(ID) (3)"; SQL statement:
delete from lp_app where id=? [23503-199]

I am obviously doing something wrong, but I don't know where to look. I guess I am not using the @ManyToMany annotation right or perhaps it is the wrong annotation for my use case.

Thank you very much.

Answer 1

You need to add cascade attribute to tell hibernate not to delete the entity on delete operation. There are different options for cascade. Refer to this link to understand the different options.

Answer 2

The short version of the answer is that you are trying to delete a record that has an existing relationship with another record.