[jira] [Commented] (OAK-6905) Query engine: support coalesce function as in-built method

["Thomas Mueller (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/OAK-6905?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16253085#comment-16253085 ] 

Thomas Mueller commented on OAK-6905:
-------------------------------------

The patch looks very good to me!

For xpath, I think in _theory_ the "fn" in "fn:coalesce" is reserved for built-in xpath functions. But I don't see a good alternative... I guess "jcr" is reserved for the JCR standard. But using "oak" sounds weird. So I'm fine with both "fn" and "jcr".

> Query engine: support coalesce function as in-built method
> ----------------------------------------------------------
>
>                 Key: OAK-6905
>                 URL: https://issues.apache.org/jira/browse/OAK-6905
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: core, lucene, query
>            Reporter: Vikas Saurabh
>            Assignee: Vikas Saurabh
>             Fix For: 1.8, 1.7.12
>
>
> Sometimes the content structure stores semantically similar properties at different locations (due to content evolution or different locations genuinely represent different values).
> e.g. say a content represent a real world image as {{..../file1.jpg/jcr:content/file}}. Where {{jcr:content/metadata/exif:title}} could be title of image from exif data, {{jcr:content/jcr:title}} could be title explicitly set by user.
> While displaying a title, it probably makes sense to show {{jcr:title}} first and fallback to {{exif:title}} and then probaly to node name if nothing else works out.
> it'd would be useful to have such overlaying be conveyed to query engine too for lookup, ordering (and, of course, indexing). As a method name, sql colesce is exactly what should serve this purpose.



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