I have some data which looks something like this:
<wrapper>
<inner a="1"/>
<inner a="2" b="3"/>
</wrapper>
The attribute b may or may not be present on each inner element. My aim is to find all documents containing at least one inner element that doesn't have attribute b.*
This similar question proposes the answer:
cts:not-query(cts:element-attribute-value-query(xs:QName('inner'), xs:QName('b'), '*', ("wildcarded"))))
but that doesn't work, because some inner elements on the same document may have attribute b, and not-queries work on the entire fragment, so a mixed case like the example above would not be returned. Wrapping it in an element-query doesn't help, and cts:and-not-query seems to behave the same way.
I have also tried attacking the problem using co-occurrence/values functions to read the values of relevant attributes a, but that also seems to be impossible. It might have been possible with proximity settings on co-occurrences calls except there is no element text, so the attribute are indexed with the same word positions.
Are there any alternatives to the blunt xpath?
//inner[@a and not(@b)]
You can always make the xpath more complicated if simplicity isnt your goal. How about this one: (it more accurately answers the exact question of 'return all documents that contain 'innner' elements that do not have an atribute @b'
doc()[exists(//inner[not(@b)])]
I do not know how well this is optimized -- some xpath expressions optimize down to the equivalent cts: query and some do not.
There is another 'trick' involving combining cts expressions represented as maps. Take the results of 2 searches, use the options that return the results as a map, then you can use the operations on this page https://developer.marklogic.com/blog/im-a-map to do extremely efficient set operations (union, intersection, difference etc). When properly constructed, this technique can be as fast as 'native' cts searches --- the cts searches use the same general technique internally for resolving results.
Make the XPath a path range index. //inner[@a and not(@b)]
, or if there's no element text, //inner[@a and not(@b)]/@a
, then do
cts:path-range-query('//inner[@a and not(@b)]/@a','>','')
This happens to also allow us to efficiently answer the question of which @a
values have a missing @b
, using cts:values
.
cts:not-in-query
has the necessary behaviour to make this work where cts:and-not-query
doesn't. Eg
cts:not-in-query(
cts:element-query(xs:QName('inner'), cts:true-query()),
cts:element-attribute-query(xs:QName('inner'), xs:QName('b'),'*','wildcarded')
)
Finds all 'inner' elements at positions that do not match the positions of 'inner' elements with attribute b.
Element position index must be enabled. Wildcard index must be enabled.
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