org.hibernate.exception.ConstraintViolationException only during unit test, Cascade Delete not working - spring

Question

I have a Spring Kotlin project where I use JPA (Hibernate?) entities to map my database tables.
A Project is linked to multiple ProjectMaps. When a Project is deleted, I want all the ProjectMaps to be deleted also.
The DDL for my local H2 db is as follows.
CREATE TABLE IF NOT EXISTS "project" (
id INT AUTO_INCREMENT PRIMARY KEY,
other fields...
);
CREATE TABLE IF NOT EXISTS "project_map" (
project_id INT NOT NULL,
tag_id INT NOT NULL,
CONSTRAINT pk_project_id_tag_id PRIMARY KEY (project_id, tag_id),
CONSTRAINT fk_project_map_project_id
FOREIGN KEY (project_id) REFERENCES "project" (id)
ON DELETE CASCADE
ON UPDATE CASCADE,
CONSTRAINT fk_project_map_tag_id
FOREIGN KEY (tag_id) REFERENCES "tag" (id)
ON DELETE CASCADE
ON UPDATE CASCADE
);
The entities are as follows.
Project
#Entity
#Table(name = "project")
class Project(
other fields...,
#JsonIgnore
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
var id: Long = 0,
) {
#JsonIgnore
#OneToMany(mappedBy = "projectMapId.project", cascade = [CascadeType.ALL], orphanRemoval = true)
val projectMaps = mutableSetOf<ProjectMap>()
}
ProjectMap
#Entity
#Table(name = "project_map")
class ProjectMap(
#EmbeddedId
var projectMapId: ProjectMapId,
) {
override fun equals(other: Any?): Boolean {
if (this === other) return true
if (other !is ProjectMap) return false
if (projectMapId != other.projectMapId) return false
return true
}
override fun hashCode(): Int {
return projectMapId.hashCode()
}
}
#Embeddable
class ProjectMapId(
#ManyToOne
#JoinColumn(name = "project_id", nullable = false, referencedColumnName = "id")
var project: Project,
#ManyToOne
#JoinColumn(name = "tag_id", nullable = false, referencedColumnName = "id")
var tag: Tag,
) : Serializable {
override fun equals(other: Any?): Boolean {
if (this === other) return true
if (other !is ProjectMapId) return false
if (project != other.project) return false
if (tag != other.tag) return false
return true
}
override fun hashCode(): Int {
var result = project.hashCode()
result = 31 * result + tag.hashCode()
return result
}
}
I have a ProjectRepository interface that extends JpaRepository. In my code somewhere I call projectRepo.deleteAllInBatch(projectsToBeDeleted), and when I run it I see that the ProjectMaps are indeed deleted together with the Projects. But when I write a unit test for that method, I get this error.
[main] ERROR org.hibernate.engine.jdbc.spi.SqlExceptionHelper.logExceptions - Referential integrity constraint violation: "FKM2O7A1Y4HFNXYHQEYBQI9AABY: PUBLIC.PROJECT_MAP FOREIGN KEY(PROJECT_ID) REFERENCES PUBLIC.PROJECT(ID) (CAST(1 AS BIGINT))"; SQL statement:
delete from project where id=? [23503-210]
[main] ERROR com.dbs.localisemanagement.exception.RestExceptionHandler.handleAllUncaughtException - [L9y5j][500][1-Unknown] could not execute statement; SQL [n/a]; constraint ["FKM2O7A1Y4HFNXYHQEYBQI9AABY: PUBLIC.PROJECT_MAP FOREIGN KEY(PROJECT_ID) REFERENCES PUBLIC.PROJECT(ID) (CAST(1 AS BIGINT))"; SQL statement:
delete from project where id=? [23503-210]]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement
org.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint ["FKM2O7A1Y4HFNXYHQEYBQI9AABY: PUBLIC.PROJECT_MAP FOREIGN KEY(PROJECT_ID) REFERENCES PUBLIC.PROJECT(ID) (CAST(1 AS BIGINT))"; SQL statement:
delete from project where id=? [23503-210]]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement
The error is at this line projectRepo.deleteAllInBatch(projectsToBeDeleted), so I see that it is because there are still existing ProjectMaps that's why the Projects cannot be deleted.
I reckon it is because the Cascade Delete is not working during unit test, but I don't know why. Anyone has any idea on this?