CODEWITHSUNDEEP
xmlxpath
jira
jira

Reputation: 3944

Confusion regarding descendant axis and '//'

Structure of a document:

<program>
 <projectionDay>
   <projection/>
   <projection/>
 </projectionDay>
 <projectionDay>
   <projection/>
   <projection/>
 </projectionDay>
</program>

I want to select the first and last projection ( across the whole document).

This returns it:

/descendant::projection[position() = 1 or position() = last()]

This returns first and last within a projectionDay

//projection[position() = 1 or position() = last()]

Why is that so?

Upvotes: 1

Views: 62

Answers (1)

Jens Erat
Jens Erat

Reputation: 38672

Your first query using descendant fetches all <projection/> elements, then filters this result set for the first and last element:

/descendant::projection[position() = 1 or position() = last()]

// is an abbreviation for /descendant-or-self::*/. So your second query actually means

/descendant-or-self::*/projection[position() = 1 or position() = last()]

which looks into all elements (here: each <projectionDay/>, and returns the first and last <projection/> element inside this element.

To return the first and last element over all <projeectionDay/>s, put everything before the predicate into parentheses:

(/descendant-or-self::*/projection)[position() = 1 or position() = last()]

or abbreviated:

(//projection)[position() = 1 or position() = last()]

Upvotes: 5

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