Tag: Database

I created the table as stated in the hibernate Bidirectional @ManyToMany documentation. I did exactly the same as shown.

When I add a person, I get the following table:

If you look closely, you will notice that there is a violation of one of the main principles of normalization, that is, information redundancy. Repeats several times New York and Los Angeles

How to add a person correctly so as not to violate the normalization of the database tables, so that there is no data redundancy?

Person.java

    @Entity(name = "Person")
    public class Person {

        @Id
        @GeneratedValue
        private Long id;

        private String name;

        @ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
        private List<Address> addresses = new ArrayList<>();

        public Person() {
        }

        public Person(String name) {
            this.name = name;
        }

        // Getters and setters are omitted for brevity

        public void addAddress(Address address) {
            addresses.add( address );
            address.getOwners().add( this );
        }

        public void removeAddress(Address address) {
            addresses.remove( address );
            address.getOwners().remove( this );
        }
    }

Address.java

    @Entity(name = "Address")
    public class Address {

        @Id
        @GeneratedValue
        private Long id;

        private String street;

        @ManyToMany(mappedBy = "addresses")
        private List<Person> owners = new ArrayList<>();

        public Address() {
        }

        public Address(String street) {
            this.street = street;
        }

        // Getters and setters are omitted for brevity
    }

LifecycleController.java

    @Controller
    public class LifecycleController {

        @Autowired
        ServiceJpa serviceJpa;


        @GetMapping(value = "/savePerson")
        public String savePersonAddress () {


            Person person1 = new Person("Jack");

            Address address1 = new Address( "New York" );
            Address address2 = new Address( "Los Angeles" );

            person1.addAddress( address1 );
            person1.addAddress( address2 );

            serviceJpa.savPerson( person1 );


            return "/savePerson";
        }

    }