How can I use the Xpath function 'contains()' to return nothing if it's search param is blank or missing/false?

Question

I'm trying to write an Xpath Statement (1.0) that can read info from a 'search' node and perform a search using it.

I was making some nice progress, but stumbled across an issue where if an attribute (used for a value in the search) is empty or doesn't exist, it fails.

Code Edited to simplify Example:

So Here is my sample XML:

<xml>
    <files>
        <file name="foo" description="" rating="4"/>
        <file name="food" description="" rating="4"/>
        <file name="foobar" description="" rating="3"/>
        <file name="bar" description="" rating="3"/>
        <file name="barter" description="" rating="3"/>
        <file name="barterer" description="" rating="2"/>
    </files>
    <searches>
        <search id="1">
            <exclude>
                <file term="foo"/>
            </exclude>
        </search>
    </searches>
</xml>

And working XPATH:

//files/file[
            not(contains(@name, //search[@id='1']/exclude/file/@term))
]

It works as expected...

However if the an expected attribute is missing or empty it will fail to work. I think because: contains(@attrib, "") matches everything for some-reason, therefore a not() will always match nothing if the attribute is "" or not present.

For Example, if I alter the exclude fragment of XML to this it fails:

            <exclude>
                <file term=""/>
            </exclude>

with this too:

            <exclude></exclude>

Is there a way to Check for an empty value and not perform the select? or is there perhaps a better way of structuring the Logic. Bare in mind I cannot use Conditionals or the other functions in Xpath2.0.

Answer 1

Why does the Xpath function contains() return everything if it search param is blank or missing?

Because that is what the XPath specification says the contains() function should do:

If the value of $arg2 is the zero-length string, then the function returns true.

You could adjust your XPath and simplify some of the conditions with the following:

//files/file[
            (  
                (
                    not(//search[@id='1']/include/file/@term)
                    or
                    (
                    contains(@name, //search[@id='1']/include/file/@term) 
                    or
                    contains(@description, //search[@id='1']/include/file/@term) 
                    ) 
                )
                or
                contains(@rating, //search[@id='1']/include/file/@rating)   
            )    
            and 
            ( 
                 (
                    not(//search[@id='1']/exclude/file/@term)
                    or
                    (
                    not(contains(@name, //search[@id='1']/exclude/file/@term)) 
                    and
                    not(contains(@description, //search[@id='1']/exclude/file/@term))
                    )
                )
                and
                (
                    not(//search[@id='1']/exclude/file/@rating)
                    or
                    not(contains(@rating, //search[@id='1']/exclude/file/@rating))
                )
            )

            ]