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https://issues.apache.org/jira/browse/WICKET-6279?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15676396#comment-15676396
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Martin Grigorov commented on WICKET-6279:
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Thank you for the report!
Yes, I think the only workaround is to return a dynamic model (like AROM) that
returns these special values. This way they are not serialized at all.
I think the problem could be fixed by implementing
AttributeModifier#readResolve() that checks whether the deserialized object is
one of those and return the special constants in this case.
[~dashorst] You are the expert here! :-)
> AttributeModifier.VALUELESS_ATTRIBUTE_REMOVE does not work after
> deserialisation
> --------------------------------------------------------------------------------
>
> Key: WICKET-6279
> URL: https://issues.apache.org/jira/browse/WICKET-6279
> Project: Wicket
> Issue Type: Bug
> Components: wicket
> Affects Versions: 7.2.0
> Environment: Tomcat 7.0
> Windows 7
> Reporter: Sven Ackermann
> Labels: attribute, behavior
>
> The magic values {{AttributeModifier.VALUELESS_ATTRIBUTE_REMOVE}} and
> {{AttributeModifier.VALUELESS_ATTRIBUTE_ADD}} do not work correctly after
> they have been deserialized.
> Imagine you have a page with a component that has sth. added like this:
> {code:java}
> component.add(AttributeModifier.replace("myattribute",
> AttributeModifier.VALUELESS_ATTRIBUTE_ADD));
> component.add(AttributeModifier.replace("anotherattribute",
> Model.of(AttributeModifier.VALUELESS_ATTRIBUTE_ADD)));
> component.add(AttributeModifier.replace("thirdattribute", new
> StringResourceModel("myresourcekey").setDefaultValue(AttributeModifier.VALUELESS_ATTRIBUTE_ADD)));
> {code}
> Once we navigate away from the page, it gets serialized including the String
> value "VA_ADD" for {{AttributeModifier.VALUELESS_ATTRIBUTE_ADD}}. When we go
> back (e.g. with browser back button), it is deserialized. But then the
> deserialized String "VA_ADD" is not anymore the same as
> {{AttributeModifier.VALUELESS_ATTRIBUTE_ADD}}, so we have an attribute added
> to our component with value "VA_ADD".
> I'm not sure how this can be resolved or if it can be resolved at all. My
> workaround is to use an {{AbstractReadOnlyModel}} that always returns
> {{AttributeModifier.VALUELESS_ATTRIBUTE_ADD}}, so that special value is not
> serialized at all.
> If it's not possible to manage the deserialisation, then there should be at
> least some documentation about this problem and maybe convenience code using
> my workaround with {{AbstractReadOnlyModel}} could be provided.
> Thanks,
> Sven
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