[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-5409) bag and idbag should implement equals() and hashCode() the same way as other collections

[Martin Burger (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-5409?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=44491#comment-44491 ] 

Martin Burger commented on HHH-5409:
------------------------------------

This - IMHO - strange behavior can result in bugs which are very cumbersome to debug. For instance, I have a history of some states. In my class History, I use an ArrayList of instances of class State.

// states is 'life cycle object' -> cascading
@OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, orphanRemoval = true)
private final List<State> states = new ArrayList<State>();

History's equals() method looks like the following one:

public final boolean equals(Object obj) {
    if (this == obj) {
        return true;
    }
    if (obj == null) {
        return false;
    }
    if (!(obj instanceof History)) {
        return false;
    }
    History other = (History) obj;
    // we do not use fields to ensure compatibility with lazy loading
    if (!Objects.equal(getStates(), other.getStates())) {
        return false;
    }
    return true;
}

getStates() is a rather less exciting getter method.

In my unit tests, the model behaves like expected. Especially, method History.equals() works as expected (it is well tested by equalsverifier).

However, when I test above the persistence layer, it happens that two history instances are not equal, although they contain the same states.

How could I persist such a history properly using Hibernate?

> bag and idbag should implement equals() and hashCode() the same way as other collections
> ----------------------------------------------------------------------------------------
>
>                 Key: HHH-5409
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-5409
>             Project: Hibernate Core
>          Issue Type: Bug
>          Components: core
>    Affects Versions: 3.3.1
>            Reporter: Dmitry Katsubo
>
> bags/idbags behave in inconsistent way in comparison to set/list/map in respect to {{equals()}} and {{hashCode()}}.
> In {{[PersistentBag.java|http://fisheye.jboss.org/browse/Hibernate/core/trunk/core/src/main/java/org/hibernate/collection/PersistentBag.java?r=HEAD#l510]}} {{equals()}} and {{hashCode()}} methods are commented and in {{[PersistentIdentifierBag.java|http://fisheye.jboss.org/browse/Hibernate/core/trunk/core/src/main/java/org/hibernate/collection/PersistentIdentifierBag.java?r=HEAD]}} not present.
> {{[PersistentMap.java|http://fisheye.jboss.org/browse/Hibernate/core/trunk/core/src/main/java/org/hibernate/collection/PersistentMap.java?r=HEAD#l449]}}, {{[PersistentSet.java|http://fisheye.jboss.org/browse/Hibernate/core/trunk/core/src/main/java/org/hibernate/collection/PersistentSet.java?r=HEAD#l428]}}, {{[PersistentList.java|http://fisheye.jboss.org/browse/Hibernate/core/trunk/core/src/main/java/org/hibernate/collection/PersistentList.java?r=HEAD#l484]}} however implement {{equals()}} and {{hashCode()}} methods correctly.
> The intention of this is clear: to avoid loading of the lazy collection on simple {{equals()}} call.
> * I think that it is a task for the end application to handle lazy collections as it is aware about this situation.
> * If there is a strong demand of not loading collections on {{equals()}} call for some applications, I suggest to make this behaviour configurable via additional attribute in XML mapping for all collections.
> * The behaviour should be documented as suggested in HHH-1642. I personally spend hours debugging before I understood why lists behave differently from bags.
> Probably relative issues:
> * HHH-3771 ({{equals()}} for lazy loaded objects)
> * HHH-1642 ({{equals()}} for {{[AbstractPersistentCollection.SetProxy|http://fisheye.jboss.org/browse/Hibernate/core/trunk/core/src/main/java/org/hibernate/collection/AbstractPersistentCollection.java?r=HEAD#l636]}}) 

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