I was just wondering if there is a shorter way of writing an XPath query to find all HREF values containing at least one of many search values?
What I currently have is the following:
//a[contains(#href, 'value1') or contains(#href, 'value2')]
But it seems quite ugly, especially if I were to have more values.
First of all, in many cases you have to live with the "ugliness" or long-windedness of expressions if only XPath 1.0 is at your disposal. Elegance is something introduced with version 2.0, I'd daresay.
But there might be ways to improve your expression: Is there a regularity to the href attributes you'd like to find? For instance, if it is sufficient as a rule to say that the said href attribute values must start with "value", then the expression could be
//a[starts-with(#href,'value')]
I know that "value1" and "value2" are most probably not your actual attribute values but there might be something else that uniquely identifies the group of a elements you're after. Post your HTML input if this is something you want us to help you with.
Personally, I do not find your expression ugly. There is just one or operator and the expression is quite short and readable. I take
if I were to have more values.
to mean that currently, there are only two attribute values you are interested in and that your question therefore is a theoretical one.
In case you're using XPath 2 and would like to have exact matches instead of also matches only containing part of a search value, you can shorten with
//a[#href = ('value1', 'value2')]
For contains() this syntax wouldn't work as the second argument of contains() is only allowed to be 0 or 1 value.
In XPath 2 you could also use
//a[some $s in ('value1', 'value2') satisfies contains(#href, $s)]
or
//a[matches(#href, "value1|value2")]
Related
I have an element with three occurences on the page. If i match it with Xpath expression //div[#class='col-md-9 col-xs-12'], i get all three occurences as expected.
Now i try to rework the matching element on the fly with
substring-before(//div[#class='col-md-9 col-xs-12'], 'Bewertungen'), to get the string before the word "Bewertungen",
normalize-space(//div[#class='col-md-9 col-xs-12']), to clean up redundant whitespaces,
normalize-space(substring-before(//div[#class='col-md-9 col-xs-12'] - both actions.
The problem with last three expressions is, that they extract only the first occurence of the element. It makes no difference, whether i add /text() after matching definition.
I don't understand, how an addition of normalize-space and/or substring-before influences the "main" expression in the way it stops to recognize multiple occurences of targeted element and gets only the first. Without an addition it matches everything as it should.
How is it possible to adjust the Xpath expression nr. 3 to get all occurences of an element?
Example url is https://www.provenexpert.com/de-de/jazzyshirt/
The problem is that both normalize-space() and substring-before() have a required cardinality of 1, meaning can only accept one occurrence of the element you are trying to normalize or find a substring of. Each of your expressions results in 3 sequences which these two functions cannot process. (I probably didn't express the problem properly, but I think this is the general idea).
In light of that, try:
//div[#class='col-md-9 col-xs-12']/substring-before(normalize-space(.), 'Bewertung')
Note that in XPath 1.0, functions like substring-after(), if given a set of three nodes as input, ignore all nodes except the first. XPath 2.0 changes this: it gives you an error.
In XPath 3.1 you can apply a function to each of the nodes using the apply operator, "!": //div[condition] ! substring-before(normalize-space(), 'Bewertung'). That returns a sequence of 3 strings. There's no equivalent in XPath 1.0, because there's no data type in XPath 1.0 that can represent a sequence of strings.
In XPath 2.0 you can often achieve the same effect using "/" instead of "!", but it has restrictions.
When asking questions on StackOverflow, please always mention which version of XPath you are using. We tend to assume that if people don't say, they're probably using 1.0, because 1.0 products don't generally advertise their version number.
Can't get any idea to cement the two expressions into one xpath. They both fall under the same class "pagination". I need to use that in a loop. I tried separately like this:
//div[#class='pagination']//a/#href
//div[#class='pagination']//a[contains(#class,'next')]/#href
Elements for the expression:
<div class="pagination"><p><span>Showing</span>1-30
of 483<span>results</span></p><ul><li><span class="disabled">1</span></li><li>2</li><li>3</li><li>4</li><li>5</li><li>Next</li></ul></div>
There are many ways you can combine two XPath expressions. One way, for example, is to use the union operator "|". Whether that's the right operator to use depends on what you want to achieve. Unfortunately you forget to tell us what you want to achieve, so that might not be the right operator for your purposes.
I am developing an application that accepts user-defined XPath expressions and employs them as part of its runtime operation.
However, I would like to be able to infer some additional data by programmatically manipulating the expression, and I am curious to know whether there are any situations in which this approach might fail.
Given any user-defined XPath expression that returns a node set, is it safe to wrap it in the XPath count() function to determine the number of nodes in the set:
count(user_defined_expression)
Similarly, is it safe to append an array index to the expression to extract one of the nodes in the set:
user_defined_expression[1]
Well an XPath expression (in XPath 1.0) can yield a node-set or a string or a number or a boolean and doing count(expression) only makes sense on any expression yielding a node-set.
As for adding a positional predicate, I think you might want to use parentheses around your expression i.e. to change /root/foo/bar into (/root/foo/bar)[1] as that way you select the first bar element in the node-set selected by /root/foo/bar while without them you would get /root/foo/bar[1] which would select the first bar child element of any foo child element of the root element.
Are you checking that such user-defined expressions always evaluate to node-set?
If yes, first Expr is ok. Datatype will be correct for fn:count
Second one is a lot trickier, with a lot of situations there predicate will overweight axis, for example. Check this answer for a simple analysis. It will be difficult to say, what a user really meant.
A more robust approach would be to convert the XPath expression to XQueryX, which is an XML representation of the abstract syntax tree; you can then do XQuery or XSLT transformations on this XML representation, and then convert back to a modified XPath (or XQuery) for evaluation.
However, this will still only give you the syntactic structure of the expression; if you want semantic information, such as the inferred static type of the result, you will probably have to poke inside an XPath process that exposes this information.
I'm looking to select a collection of elements based on an array of ID names. I'm currently using a giant OR statement essentially:
//*[#id='apple']|//*[#id='orange']|//*[#id='banana']
But building that string manually seems messy. Is there something like a nice SQL-esque "WHERE IN [a,b,c]" operator that I could be using?
I am using the HTTPAgilityPack for ASP.Net which I think equates to XPath1.o (feel free to correct me on that.)
Thanks.
First, you could simplify this by using or. This avoids repeating the //* multiple times although you till specify the #id= part multiple times:
//*[#id='apple' or #id='orange' or #id='banana']
A more elegant solution is to check against a list of acceptable ids. Now if you're using XPath 1.x then you'll have to do a bit of gymnastics to get contains() to do your bidding. Specifically, notice that I've got spaces on both ends of the first string, and then concatenate spaces to each end of #id before looking for a match. This is to prevent an #id of "range" from matching, for example.
//*[contains(' apple orange banana ', concat(' ', #id, ' '))]
If you have are using XPath 2.0 then the way forward is simpler thanks to the addition of sequences to the language:
//*[exists(index-of(('apple', 'orange', 'banana'), #id))]
Use:
//*[contains('|apple|banana|orange|', concat('|',#id, '|'))]
In case some of the id attributes may contain the "|" character, use another instead, that is known not to be present in the value of any of the id attributes.
An XPath 2.0 solution:
//*[#id=('apple', 'orange', 'banana')]
Using apricot, it is pretty easy to see how I can extract all elements with a given id or class using a CSS Selector. Is it possible to extract elements from a document based on whether some attribute of those elements matches against some regular expression?
If you mean do something like:
doc.search("//div[#id=/regex/]")
then I don't think it can be done. The alternative is to find all elements and then iterate through the results deleting those that don't match a regex.
result = doc.search("//div")
result.delete_if (|x| x.to_s !~ /regex/)
There are lots of alternative approaches. This thread has two other suggestions: Hpricot and Regular Expression.
Note, depending on exactly what it is you are trying to match you may be able to use the "Supported, but different" syntaxes available on the Hpricot Wiki, e.g:
E[#foo$=“bar”]
Matches an E element whose “foo”
attribute value ends exactly with the
string “bar”