JPA + Hibernate + Spring + OneToMany delete cascade

Relationships in JPA are always unidirectional, unless you associate the parent with the child in both directions. Cascading REMOVE operations from the parent to the child will require a relation from the parent to the child (not just the opposite).

So here you need to change unidirectional relationship to bi-directional.

for more details refer this link.

Look at orphanRemoval option:

@OneToMany(cascade = CascadeType.REMOVE, orphanRemoval = true)

Here is complete explication about CascadeType.REMOVE and orphanRemoval.

Good luck!