To save data to foreign key attribute in JPA using java persistence with dropdown element using EJB

Question

Hi I want to save data form jsp file to derby database using jpa.But cannot save the data to the database. In productorder page: Where I need save value

public class ProductOrder implements Serializable {
    @ManyToOne
    @JoinColumn(name = "customerId")
    private Customer customer;

    //getter 
    //setter
}

In EJB file:

public class OrderEJB {

    @PersistenceContext(unitName = "com.mycompany_Ebusiness_war_1.0-SNAPSHOTPU")
    private EntityManager entityManager;

    public ProductOrder placeOrder(ProductOrder productOrder) {
        entityManager.persist(productOrder);
        return productOrder;
    }
}

In jsp(xhtml file) file:

<h:form>
    <h:selectOneMenu value="#{orderController.customer}" >
        <f:selectItems value="#{orderController.customerList}" var="c" itemLabel="#{c.name}" itemValue="#{c.id}" />
    </h:selectOneMenu>
    <h:commandButton value="Place a Order" action="#{orderController.placeOrder}"/>
</h:form>

My converter file:

public class CustomerConverter implements Converter{ 

    private transient EntityManager em; 

    @Override
    public Object getAsObject(FacesContext context, UIComponent component, String value) { 
        return em.find(Customer.class, new Integer(value));
    }

    @Override
    public String getAsString(FacesContext fc, UIComponent uic, Object o) { 
        return ((Customer) o).getId().toString(); 
    }

}

Answer 1

Code errors

Your code contains some errors/missing point:

1. missing optional referencedColumnName: as stated in comment, the JoinColumn annotation is missing an attribute. The attribute is optional but I like to make sure what is referenced:

   public class ProductOrder implements Serializable {
       @ManyToOne
       // replace "id" with the appropriate column name
       @JoinColumn(name = "customerId", referencedColumnName = "id")
       private Customer customer;
   
       //getter 
       //setter
   }
   

   the referencedColumnName is the FOREIGN KEY parallel. The above annotation is reflecting the constraint:

   FOREIGN KEY (customerId) REFERENCES customer_table(id)
   

2. You're using JSF, not JSP. Please refer to this question for more information.

3. Your selectOneMenu is incorrect:

   <h:form>
       <h:selectOneMenu value="#{orderController.customer}" converter="customerConverter">
           <f:selectItems value="#{orderController.customerList}" var="c"
                          itemLabel="#{c.name}" itemValue="#{c}" />
       </h:selectOneMenu>
       <h:commandButton value="Place a Order" action="#{orderController.placeOrder}"/>
   </h:form>
   

   • a converter tag is missing. BalusC offered an awesome explanation here.
   • your itemValue is supposed to refer to your customer object, not the customer id. Hence, it should be itemValue="#{c}.

4. You're converting the wrong value: your converter class converts customerId <-> customer object whereas in your selectOneMenu, you want to convert customer name <-> customer object

5. Your converter class may be missing the @FacesConverter annotation

Solving

You'll need to solve each point one by one:

1. Converter: Choose what you want to display in your form, if you want to display the customer name, then your converter should look like:

   @FacesConverter
   @RequestScoped
   public class CustomerConverter implements Converter{ 
   
       // you would normally inject your EJB here. Please refer to BalusC's 
       // answer for more information
       // private transient EntityManager em;
       @EJB
       private CustomerService customerService;
   
       @Override
       public Object getAsObject(FacesContext context, UIComponent component, String value) {
           return customerService.findByName(value);
       }
   
       @Override
       public String getAsString(FacesContext fc, UIComponent uic, Object o) { 
           return ((Customer) o).getName();
       }
   
   }
   

   in your customer service:

   @Stateless
   public class CustomerServiceImpl implements CustomerService{
   
       @Override
       public Customer findByName(String name){
           // assuming you have a name query to fetch by name,
           // otherwise use em.createQuery(...)
           TypedQuery<Customer> query = em.createNamedQuery("Customer.findByName", Customer.class);
           query.setParameter("name", name);
           return query.getSingleResult();
       }
   }
   

2. when your converter is ready, adjust your h:selectOneMenu and f:selectItems accordingly