Hi Wilko ,

the issue is caused by a wrong use of mappedBy ,

public static class B {

    @OneToMany(mappedBy = "aClass", fetch = FetchType.LAZY)
	private List<C> cClasses;
}

public static class C {

    @ManyToOne(fetch = FetchType.LAZY)
	private A aClass;
}

for a B ↔︎ C relationship you are specifying as a bidirectional target a property of type A while it should be of type B . I think you should just remove the mappedBy from the @OneToMany .