[Bug 27630] New: Branching based on the XDM value returned by an updating expression

https://www.w3.org/Bugs/Public/show_bug.cgi?id=27630

            Bug ID: 27630
           Summary: Branching based on the XDM value returned by an
                    updating expression
           Product: XPath / XQuery / XSLT
           Version: Working drafts
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Update 3.0
          Assignee: john.snelson@marklogic.com
          Reporter: john.snelson@marklogic.com
        QA Contact: public-qt-comments@w3.org

XQuery Update 3.0 still doesn't have a way to make a decision based on the 
result of an updating expression. All the conditional expressions in the 
language are restricted from having an updating expression in their test 
expressions (if, typeswitch, switch, where etc.). In particular this 
makes it impossible to satisfy the following use case. There is also no way to
assign the XDM value of an updating expression to a variable.

Encapsulation Use Case

This use case shows a function which checks if a given username is known 
and logs the event. Both the storage format for usernames and the fact 
that the event is being logged should be hidden from the function's 
caller (encapsulated), since these requirements could change later in 
the development process.

declare %updating function local:check-username($username as xs:string)
    as xs:boolean
{
    let $found := $username = collection()//user/@name
    return (
      insert node
        <access-attempt>
          <timestamp>{fn:current-dateTime()}</timestamp>
          <user-name>{$username}</user-name>
          <access-allowed>{if($found) then "Yes" else "No"}
          </access-allowed>
        </access-attempt>
      into doc("log.xml")/*,
      $found
    )
};

declare variable $username as xs:string external;

<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
      <title>Looking up user name</title>
    </head>
    <body>
    {
      if(local:check-username($username)) then
        <p>Welcome, {$username}! Your previous login was:
        {
          doc("log.xml")//access-attempt[username = $username
            and access-allowed = "Yes"]/timestamp/string()
        }
        </p>
      else
        <p>I don't know you!</p>
    }
    </body>
</html>

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Received on Tuesday, 16 December 2014 18:10:06 UTC