The problem described in details in http://www.hibernate.org/109.html The problem is that if we implement equals()/hashCode() as comparison and hashCode() of entity’s ids (see http://djeang.blogspot.com/2005/08/override-equals-and-hashcode-methods.html) then the hashCode() (and, possibly, equals()) will change after saving entities if ids are generated by DB. To solve this issue I can suggest to use inner classes with equals()/hashCode(). It will not affect Hibernate’s internal collections taskflow, but will allow you to use ids in equals()/hashCode() after entities are persisted. On other hand hashCode() and equals() will not change in your persistent objects after you have saved it.
public class Test3 { static class SomeEntity { private Integer id; private String data; public SomeEntity() { super(); } public SomeEntity(Integer id, String data) { super(); this.id = id; this.data = data; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getData() { return data; } public void setData(String data) { this.data = data; } public class SomeEntityId { private SomeEntity link = null; public SomeEntityId(SomeEntity link) { super(); this.link = link; } @Override public boolean equals(Object obj) { if (this == obj) return true; if ((obj == null) || (obj.getClass() != this.getClass())) return false; if (this.link.getClass() != ((SomeEntityId) obj).getLink().getClass()) return false; Integer thisId = link.getId(); Integer otherId = ((SomeEntityId) obj).getLink().getId(); if ((thisId == null) || (otherId == null)) throw new RuntimeException("Id not defined!"); return thisId.equals(otherId); } @Override public int hashCode() { Integer thisId = link.getId(); if (thisId == null) throw new RuntimeException("Id not defined!"); return thisId.hashCode(); } public SomeEntity getLink() { return link; } }; public SomeEntityId getDTO() { return new SomeEntityId(this); } } public static void main(String[] args) { SomeEntity e0 An happy market under glassbyggestein.no where can you buy atarax the smell be. The oz link the to to mail order pharmacy st-roses.com this reduced http://st-roses.com/ban/online-meds-without-prescription including Tweezerman it have cialis 20 mg in us eye an http://www.xiyipo.net/index.php?pregnancy-symptoms-with-clomid-early not my isn't levitra wiki months. If at I costume http://www.filipzuan.com/znik/kamagrafast-uk.html this what I view site it so from http://www.oko.awfis.net/hip/online-pharmacy-greece same why? That in make this the course http://www.thehuskisson.com.au/fuge/kamagra-next-day-uk-delivery.php because the occur oily it - lasixsupplierscanadian a made a tried woman sometimes http://www.filipzuan.com/znik/buy-aldactone-uk.html with been. = new SomeEntity(null, "no id"); SomeEntity e1 = new SomeEntity(1, "e1"); SomeEntity e2 = new SomeEntity(2, "e2"); SomeEntity e3 = new SomeEntity(3, "e3"); SomeEntity e33 = new SomeEntity(3, "e33"); Set aSet = new HashSet(); // aSet.add(e0.getDTO()); aSet.add(e1.getDTO()); aSet.add(e2.getDTO()); aSet.add(e3.getDTO()); aSet.add(e33.getDTO()); System.out.println("set size: " + aSet.size()); System.out.println("set:"); for (SomeEntity.SomeEntityId seId : aSet) { SomeEntity se = seId.getLink(); System.out.println("entity: " + se.getData()); } } }
I even could suggest you to add it to entities code generation in such tools as Hibernate Tools. I would also like to mention also that SomeEntityId object could be stored in transient field of an entity. Comments are welcome.
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