N-N relationship with additional fields (problems to persist data)

Question

I have an N-N relationship that works as follows:

Destination.java (N)-(N) Customerservice.java

Within this relationship there is an entity that keeps the relationship Ids, which has some more values. The name of such is Serviceitem.java

Below the Entity’s:

Destination.java

@Entity
@Table(name="destination")
public class Destination implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="id_destination")
    private Long idDestination;

    @Column(name="tenant_id", insertable=false, updatable=false)
    private Long tenantId;

    @Column(name="appear_website")
    private Boolean dtAppearWebsite;

    @Lob
    @Column(name="description")
    @NotEmpty(message="O campo \"Descrição do Destino\" não pode estar em branco.")
    private String dtDescription;

    @OneToMany(mappedBy="destination")
    private Set<ServiceItem> serviceItem;

    //Mais campos adicionais e Getters and Setters

    public Destination() {
    }
}

Customerservice.java

@Entity
@Table(name = "customer_service")
public class CustomerService implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id_customer_service")
    private Long id;

    @Column(name = "tenant_id", insertable = false, updatable = false)
    private Long tenantId;

    @Column(name = "date_service")
    @DateTimeFormat(pattern = "dd/MM/yyyy")
    @Temporal(TemporalType.DATE)
    private Date date;

    @Column(name = "average_budget")
    private BigDecimal averageBudget;

    @Column(name = "service_situation")
    private boolean situation;

    @OneToMany(cascade = CascadeType.PERSIST, mappedBy = "customerService")
    private List<ServiceItem> serviceItem;

    @OneToOne(cascade = CascadeType.PERSIST)
    @JoinColumn(name = "fk_history")
    private History history;

    @Column(name = "service_observatons")
    private String serviceObservations;

    public CustomerService() {

    }

    //Mais campos adicionais e Getters and Setters

}

Serviceitem.java

@Entity
@Table(name = "service_item")
@IdClass(ServiceItemId.class)
public class ServiceItem {

    @Id
    @ManyToOne
    @JoinColumn(name="destination_id")
    private Destination destination;

    @Id
    @ManyToOne
    @JoinColumn(name="customerService_id")
    private CustomerService customerService;

    @Column(name="tenant_id", insertable=false, updatable=false)
    private Long tenantId;   

    @Column(name="value_negotiated")
    private double valueNegotiated;

    @Enumerated(EnumType.STRING)
    @Column(name="sale_type")
    private SaleType saleType;

    @Column(name="departure_date")
    @DateTimeFormat(pattern="dd/MM/yyyy")
    @Temporal(TemporalType.DATE)
    private Date departureDate;

    @Column(name="arrival_date")
    @DateTimeFormat(pattern="dd/MM/yyyy")
    @Temporal(TemporalType.DATE)
    private Date arrivalDate;

    @Column(name="requested_destination")
    private Boolean requestedDestination;

    @Column(name="negociation_observations")
    private String negociationObservations;

    public ServiceItem() {

    }

    //Getters and Setters
}

To generate id’s there is the class Serviceitemid.java

public class ServiceItemId implements Serializable {

    private static final long serialVersionUID = 1L;

    private Long destination;
    private Long customerService;

    public Long getCustomerService() {
        return customerService;
    }
    public void setCustomerService(Long customerService) {
        this.customerService = customerService;
    }
    public Long getDestination() {
        return destination;
    }
    public void setDestination(Long destination) {
        this.destination = destination;
    }

    @Override
    public int hashCode() {
        return (int) (destination + customerService);
    }

    @Override
    public boolean equals(Object obj) {
        if(obj instanceof ServiceItemId){
            ServiceItemId serviceItemId = (ServiceItemId) obj;
            return serviceItemId.destination == destination && serviceItemId.customerService == customerService;
        }

        return false;
    }

}

Well, the question is when will I persist the data...

Dez 17, 2014 4:52:27 PM org.apache.catalina.core.StandardWrapperValve invoke
GRAVE: Servlet.service() for servlet [appServlet] in context with path [/viatge] threw exception [Request processing failed; nested exception is org.springframework.transaction.TransactionSystemException: Could not commit JPA transaction; nested exception is javax.persistence.RollbackException: Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.5.2.v20131113-a7346c6): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Column 'customerService_id' cannot be null
Error Code: 1048
Call: INSERT INTO service_item (arrival_date, departure_date, negociation_observations, requested_destination, sale_type, value_negotiated, customerService_id, destination_id, tenant_id) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)
    bind => [2016-08-01, 2015-10-01, teste, true, SUBMITTED_BUDGET, 3658.98, null, 1, 2]
Query: InsertObjectQuery(br.com.joocebox.model.ServiceItem@6e92b1b1)] with root cause
com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Column 'customerService_id' cannot be null
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
    at com.mysql.jdbc.Util.getInstance(Util.java:386)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1041)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4187)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4119)

I even understand that it is missing inform the id customerService_id in the Serviceitem.java entity, but this id will be generated automatically, as it is incorrect for me to enter the id in hand.

How could I proceed in such a case?

EDITION

Come on!

My Entity Customerservice (which refers to a service) has many destinations (in this case Destination), as many destinations may belong to many Customerservice.java (support).

Note that there is no relationship @Manytomany directly between the entities, but there is a class called Serviceitem that makes the union between the two entities.

When I will persist a Serviceitem, my id related to Destination is loaded, (because it already exists), already the Customerservice has not been persisted, so it will not have an ID which is the cause of the problem.

Answer 1

Responding to the discussion in the comments: Both the use of UUID(GUID) and ID have their pros and cons.

The more technical details I leave to the original post, which this response is based on:

Soen - Advantages-and-disadvantages-of-guid-uuid-database-Keys

Soen - how-do-you-like-your-Primary-Keys

Soen - generate-uuid-in-java

Follow a simple example, note that @Prepersist will be executed by your ORM framework. More details on Entity Systems HERE.

@Entity
@Table(name = "service_item")
public class ServiceItem {

    @Id
    //Long ? Integer ?
    private String uuid;

    @ManyToOne
    @JoinColumn(name="destination_id")
    private Destination destination;

    @ManyToOne
    @JoinColumn(name="customerService_id")
    private CustomerService customerService;


    @PrePersist
    public void init() {
        //Aqui voce gera seu GUID
        //Note que existem varios outros meios
        //Estou utilizando esse pois é nativo e pratico
        this.uuid = UUID.randomUUID().toString();
    }

    //...
}