Spring: Cannot delete or update a parent row - sql

Question

I'm very new to Spring MVC and am working on a school project that is due in less than a month. I'm facing an issue where I'm unable to delete a Customer entity without SQLIntegrityConstraintViolationException being thrown. Specifically, the error is:
Cannot delete or update a parent row: a foreign key constraint fails (e_cinema.shopping_cart, CONSTRAINT FKh7db6pdgs2ol2t6k73wn3xj75 FOREIGN KEY (customer_id) REFERENCES customer (id))
The bit I'm trying to run is
Customer customer = new Customer();
...
customerService.delete(customer);
The service delete method simply calls customerRepository.delete(customer).
Customer:
#Entity
#Getter
#Setter
#Table
public class Customer extends User {
#Column
private Boolean locked;
#JoinColumn
#OneToOne(cascade = CascadeType.ALL)
private ShoppingCart shoppingCart = new ShoppingCart();
#OneToMany(cascade = CascadeType.ALL)
private List<PaymentCard> paymentCards = new ArrayList<>();
#OneToMany(cascade = CascadeType.ALL)
private List<PurchasedTicket> purchasedTickets = new ArrayList<>();
public Customer() {
shoppingCart.setCustomer(this);
}
}
Shopping cart:
#Entity
#Getter
#Setter
#Table
public class ShoppingCart extends AbstractEntity {
#Column
private Float total;
#OneToOne(fetch = FetchType.LAZY)
private Customer customer;
#OneToMany(cascade = CascadeType.ALL)
private Set<ShoppingCartTicket> shoppingCartTickets = new HashSet<>();
}
Shopping cart ticket:
#Entity
#Getter
#Setter
#Table
public class ShoppingCartTicket extends Ticket {
#JoinColumn
#ManyToOne(fetch = FetchType.LAZY)
private ShoppingCart shoppingCart;
#JoinColumn
#ManyToOne(fetch = FetchType.LAZY)
private Screening screening;
#JoinColumn
#ManyToOne(fetch = FetchType.LAZY)
private Seat seat;
}
I'd greatly appreciate any help on what the issue could be. Also, if there's any other issues with what I have, I'd appreciate pointers on that as well. I can post more code if necessary.