7 Replies Latest reply on Nov 19, 2007 1:36 PM by David Durst

    EJB 3 Required to Override equals & hashCode

    David Durst Newbie

      Is it required that I override equals & hashCode for EJB 3 POJOs?

        • 1. Re: EJB 3 Required to Override equals & hashCode
          Andrew Rubinger Master

          Nope.

          "EJB3 Core Specification, 4.7.3" wrote:
          The container provider is responsible for providing the implementation of the equals and hashCode
          methods for the business interface, in conformance with the requirements of section 3.6.5.


          S,
          ALR

          • 2. Re: EJB 3 Required to Override equals & hashCode
            mazz Master

            You are about to open a pandora's box :)

            Google "hashCode" and "equals" as it relates to EJB3 and Hibernate.

            You'll find the answer to this question isn't as simple as you first think.

            • 3. Re: EJB 3 Required to Override equals & hashCode
              mazz Master

              A good page describing the issues I alluded to can be found on the Hibernate wiki at:

              http://www.hibernate.org/109.html

              • 4. Re: EJB 3 Required to Override equals & hashCode
                Andrew Rubinger Master

                My response was in relation to Session Beans only. :)

                S,
                ALR

                • 5. Re: EJB 3 Required to Override equals & hashCode
                  David Durst Newbie

                  Wow!
                  I am now only more confused than I was before.
                  This issue stems from a previous post that I made about my OneToMany
                  relationships only saving one child.

                  As I determined it was because my IDE (NetBeans) was created Override methods for equals() and hashCode().... So I asked this question.

                  Based on ALRubingers response I went ahead and removed these methods
                  from my POJOs and have experienced no adverse side affects in my application.

                  I have read http://www.hibernate.org/109.html

                  Which clarified very little for me besides that if I do override these methods I should use a "Business Key". This idea for some entities tweaks my head a little bit, as I see no "Business Key" for a Entity such as a Order Line.

                  Can someone give me a example of a relationship like Order -> OrderLine
                  in which equals() and hashCode() are overried properly.

                  • 6. Re: EJB 3 Required to Override equals & hashCode
                    wayne baylor Apprentice

                    go for logical equality, so if your entity has three fields:

                    @Id
                    @GeneratedValue
                    private int id;
                    
                    private String firstName;
                    
                    private String lastName;


                    then equals/hashCode should be based on first/lastName and not id.

                    • 7. Re: EJB 3 Required to Override equals & hashCode
                      David Durst Newbie

                       


                      go for logical equality, so if your entity has three fields:
                      Code:
                      @Id
                      @GeneratedValue
                      private int id;
                      private String firstName;
                      private String lastName;
                      



                      then equals/hashCode should be based on first/lastName and not id.


                      I understand this concept as you have put forth. That being that a firstName & lastName has some uniqueness.
                      This issue occurs in my mind when you have 2 Joe Smiths.
                      These to object are then considered equal when they may not actually
                      be EQUAL in reality. So to then you would say add SSN or some other
                      unique. Which in all reality replaces the Primary key. This works for
                      objects with such unique identifier.

                      Unfortunately with objects such as a Order Line where the structure are as follows:
                       @Id
                       @GeneratedValue(strategy = GenerationType.SEQUENCE)
                       private Long id;
                       private String lineStatus = OrderLine.SHIP_WHEN_COMP;
                       @Temporal(TemporalType.TIMESTAMP)
                       private Calendar requiredDate;
                       private LineQuantity quantity;
                       @Embedded
                       private PriceCost priceCost;
                       @OneToOne(cascade = CascadeType.ALL)
                       private Item item;
                       @ManyToOne
                       @JoinColumn(name="parentOrder")
                       private Order parentOrder;
                      

                      Business unique identifiers do not exist.

                      Two order lines where all attribute values are equal can exist on the same parent order.

                      Does anyone have a example of how to resolve THIS specific issue?