Order by an element while fetching documents from a directory

问题

I have to fetch all documents from a directory and am using below query to do same. Now i need to return the result which is sorted based on the effectiveDate element.Can we use order by along with this code

let $news :=xdmp:directory("/news/","1")
for $d in $news
return $d
-- Result -----

    <?xml  version="1.0" encoding="UTF-8"?>
    <NewsEntity xmlns="http://jnj.com/news">
        <uuid xmlns="">868e8a3a-058d-4b2d-8d69-0696f75ec97f</uuid>
        <headLine>HeadLine 4</headLine>
        <contributor>User 4</contributor>
        <effectiveDate>2016-08-31</effectiveDate>
    </NewsEntity>
    <?xml  version="1.0" encoding="UTF-8"?>
    <NewsEntity xmlns="http://jnj.com/news">
        <uuid xmlns="">311eeede-2560-4142-b882-b666ab08c9f8</uuid>
        <headLine>HeadLine 3</headLine>
        <contributor>User 3</contributor>
        <effectiveDate>2016-08-28</effectiveDate>
    </NewsEntity>
    <?xml  version="1.0" encoding="UTF-8"?>
    <NewsEntity xmlns="http://jnj.com/news">
        <uuid xmlns="">9bb67977-a217-425f-82e4-b4366e80d7c4</uuid>
        <headLine>HeadLine 2</headLine>
        <contributor>User 2</contributor>
        <effectiveDate>2016-08-30</effectiveDate>
    </NewsEntity>

回答1:

If you want results to be sorted efficiently, you will need a date range index on effectiveDate. Under certain conditions the query optimizer can leverage that index using order by clauses, but it might be more straight-forward to use cts:index-order with a cts:search. Something like:

cts:search(collection(),
  cts:directory-query('/news', 1),
  cts:index-order(
    cts:element-reference(
      fn:QName("http://jnj.com/news", "effectiveDate")
      "type=date"
    )
  )
)

More details can be found in the Performance Guide under "Sorting Searches Using Range Indexes"..

HTH!

回答2:

Depending on your usage criteria, you can also use a simpler "order by" expression, which sounds like what you want to do. In this case you have to make sure you point to the effectiveDate element properly, as it's in a namespace.

for $d in xdmp:directory("/news/","1")
order by $d/*:effectiveDate
return $d

来源：https://stackoverflow.com/questions/39225312/order-by-an-element-while-fetching-documents-from-a-directory

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