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https://issues.apache.org/jira/browse/LUCENE-2154?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12831521#action_12831521
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Renaud Delbru commented on LUCENE-2154:
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I see. The problem is to return to the consumer a unique attribute reference
when attributes().getAttribute is called, and then updates the references when
iterating the enums in order to propagate the attribute changes to the consumer.
I am trying to propose a (possible) alternative solution (if I understood the
problem correctly), which can avoid reflection, but could potentially need a
modification of the Attribute interface.
If the MultiAttributeSource will create its own set of unique references for
each attribute (the list of different attribute classes can be retrieved by
calling the getAttributeClassesIterator() method of the AttributeSource for
each subreader, we can then create a list of unique references, one reference
for each type of attributes), the goal is then to update these references after
each enum iteration or sub-enum change (in order to propagate the changes to
the consumer).
Unfortunately, I don't see any interface on the Attribute interface to 'copy' a
given attribute. Each AttributeImpl could implement this 'copy method', which
copies the state of a given attribute of the same class.
Then, in the MultiDocsAndPositionsEnum, after each iteration or each sub-enum
change, a call to MultiAttributeSource can be made explicitly to update the
unique references of the different attributes. This update method will under
the hood (1) check if the sub-enum is aware of the attribute class, (2) get the
attribute from the sub-enum, and (3) copy the attribute to the unique attribute
reference kept by MultiAttributeSource.
Could this solution possibly work ?
> Need a clean way for Dir/MultiReader to "merge" the AttributeSources of the
> sub-readers
> ---------------------------------------------------------------------------------------
>
> Key: LUCENE-2154
> URL: https://issues.apache.org/jira/browse/LUCENE-2154
> Project: Lucene - Java
> Issue Type: Bug
> Components: Index
> Affects Versions: Flex Branch
> Reporter: Michael McCandless
> Fix For: Flex Branch
>
>
> The flex API allows extensibility at the Fields/Terms/Docs/PositionsEnum
> levels, for a codec to set custom attrs.
> But, it's currently broken for Dir/MultiReader, which must somehow share
> attrs across all the sub-readers. Somehow we must make a single attr source,
> and tell each sub-reader's enum to use that instead of creating its own.
> Hopefully Uwe can work some magic here :)
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