spring data jpa one to many example

1. https://www.callicoder.com/hibernate-spring-boot-jpa-one-to-many-mapping-example
2.  error-
1.  object references an unsaved transient instance 
1. https://stackoverflow.com/questions/2302802/object-references-an-unsaved-transient-instance-save-the-transient-instance-be
3. https://hellokoding.com/jpa-one-to-many-relationship-mapping-example-with-spring-boot-maven-and-mysql/
4. https://dzone.com/articles/spring-data-jpa-and-database
5.