xquery beginner- how to use an if-then-else within a FLWOR statement

Question

I want to extract some content from a web page's XML equivalent, using XQuery.

Here, I want to use if-then-else -- if a specific condition is met, then one value is returned by the xquery expression, otherwise a different value is returned.

This is the expression I have with me--

I am working to extract some content from a web page.

Given below is the Xquery code I am using-- I am using a XQuery library to parse through XML which is obtained by transforming a HTML web page into XML...after that I am extracting some specific content from that XML page...

                    declare variable $doc as node() external;

                    let $select_block := $doc//div[@class="randomclass" and contains(.,'MatchingText')]
                    for $select_link in $select_block/a 
                    for $select_link_url in $select_link/@href
                        where  contains($assignee_link_url,'inassignee')  
                     return data($select_link)

Now how do I use if-then-else within this expression?

I tried to add an if-then immediately after 'return' keyword but I am getting error... Basically, if some content is found for $select_block above, then data($select_link) should be returned, otherwise the static text 'Missing Value' should be returned.

What is the correct way of using if-then-else with the above xquery expression?

Solution

If I understand what you are trying to achieve correctly, then the following should work:

declare variable $doc as node() external;
let $select_block := $doc//div[@class="randomclass" and contains(.,'MatchingText')]
return 
    if ($select_block) then
     for $select_link in $select_block/a 
        for $select_link_url in $select_link/@href
            where  contains($select_link_url,'inassignee') 
                return data($select_link)
    else 'Missing Value'

You could simplify things a little bit and eliminate the nested for loops with predicate filters selecting the anchor elements:

declare variable $doc as node() external; 
let $select_block := $doc//div[@class="randomclass" and contains(.,'MatchingText')]
return 
    if ($select_block) then
     for $select_link in $select_block/a[@href[contains(., 'inassignee')]]
         return data($select_link)
    else 'Missing Value'