Spring boot JPA save with custom primary key

How to save an entity with custom primary key?

For example, I have an entity like below:

@Entity
@Table(name = "customer")
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Customer {
  @EmbeddedId
  private CustomerCompositeKey identity;
  private String otherdata;
}
@Embeddable
@Data
@AllArgsConstructor
@NoArgsConstructor
public class CustomerCompositeKey implements Serializable {
  @Column(name = "key_one")
  private String keyOne;
  @Column(name = "key_two")
  private String keyTwo;
  
   @Override
    public boolean equals(Object o) {
      if (this == o) {
        return true;
      }
      if (!(o instanceof CustomerCompositeKey)) {
        return false;
      }
      CustomerCompositeKey that = (CustomerCompositeKey) o;
      return Objects.equals(keyOne, that.keyOne) && Objects
          .equals(keyTwo, that.keyTwo));
    }

    @Override
    public int hashCode() {
      return Objects.hash(keyOne, keyTwo);
    }

}

Repository class:

@Repository
public interface CustomerRepository extends
    JpaRepository<Customer, CustomerCompositeKey> {
}

Currently, if I simply save I am getting a unique constraint exception. So I modified the code with a select update like below. Save code:

@Transactional
public void saveCustomer(CustomerBO customer){
  Optional<Customer> customer = customerRepository.findById(customerCompositeKey);
if(customer.isPresent()) {

}else{
}
customerRepository.save(customer);
}

This is increasing my latency while saving. Is there any other way to just save without a select query? this block will be executed concurrently. customerRepository.save(customer) is already having select/update. But why am I getting a unique constraint error?