Wikibooks

XQuery/Time Comparison with XQuery

< XQuery

Motivation

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You have two identical lists of items with timestamps. You want to compare the items to see what items are newer.

Method

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We will write a function that compares the timestamps of the items in two lists.

Sample Data Sets

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let $list1 :=
<list>
   <item dateTime="2009-06-01T11:59:00.000-05:00">apples</item>
   <item dateTime="2009-02-01T11:59:00.000-05:00">bananas</item>
   <item dateTime="2009-02-01T11:59:00.000-05:00">carrots</item>
   <item dateTime="2009-02-01T11:59:00.000-05:00">eggplant</item>
   <item dateTime="2009-02-01T11:59:00.000-05:00">grapes</item>
   <item dateTime="2009-02-01T11:59:00.000-05:00">oranges</item>
</list>

let $list2 :=
<list>
   <item dateTime="2009-01-01T11:59:00.000-05:00">apples</item>
   <item dateTime="2009-02-01T11:59:00.000-05:00">bananas</item>
   <item dateTime="2009-03-01T11:59:00.000-05:00">carrots</item>
   <item dateTime="2009-02-01T11:58:00.000-05:00">eggplant</item>
   <item dateTime="2009-02-01T12:00:00.000-05:00">grapes</item>
   <item dateTime="2009-04-01T11:59:00.000-05:00">oranges</item>
</list>

Sample XQuery Function

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declare function local:older($list1 as node()*, $list2 as node()*) as node()* {
for $item1 in $list1/item
   let $item2 := $list2/item[./text() = $item1/text()]
   return
      <div>
       {attribute {'class'} 
           {if ( xs:dateTime($item1/@dateTime) lt xs:dateTime(fn:current-dateTime) )
            then 'older'
            else 'newer'
            }
       }
       {$item1/text()}
      </div>
};

Comparison Screen Image

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Sample Test Driver

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<html>
   <head>
   <style language="text/css">
  <![CDATA[
    body {font-family: Ariel,Helvetica,sans-serif; font-size: medium;}
    h2 {padding: 3px; margin: 0px; text-align: center; font-size: large; background-color: silver;}
    .left, .right {border: solid black 1px; padding: 5px;}
    .older {background-color: pink;}
    .left {float: left; width: 390px}
    .right {margin-left: 410px; width: 390px}

  ]]>
  </style>

   </head>
   <body>
      <h1>Older Items on Second List Report</h1>
      <div class="left">
         <h2>List 1</h2>
         {for $item in $list1/item return <div>{$item/@dateTime} dateTime={string(fn:current-dateTime)}</div>}
      </div>
      <div class="right">
         <h2>List 2</h2>
         {for $item in $list2/item return <div>{$item/text()} dateTime={string($item/@dateTime)}</div>}
      </div>
      <br/>
      <p>The pink items are older items.</p>
      <div class="left">
         <h2>Items on 2 Older Then 1</h2>
         {local:older($list1, $list2)}
      </div>
      <div class="right">
         <h2>Items on 1 Older Then 2</h2>
         {local:older($list2, $list1)}
      </div>
   </body>
</html>

Execute

Collating

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Alternatively, two ordered lists can be collated to derive a set of updates. Here the items are wrapped in a div to carry the added information about the merge. Items in list1 but not list2 are flagged as new, items in list 2 but not list 1 as to be deleted and items which are newer in list 1 than list 2 as newer. 


declare function local:merge($a, $b  as node()*)  as node()* {
    if (empty($a) and empty($b))
    then ()
    else  if (empty ($b) or $a[1] lt $b[1])
    then  (<div class="add">{$a[1]}</div>, local:merge(subsequence($a, 2), $b))
    else  if (empty($a) or $a[1] gt $b[1])
    then  (<div class="delete">{$b[1]}</div>,local:merge($a, subsequence($b,2)))          
   else   (<div  class="{ if (xs:dateTime($a[1]/@dateTime) gt xs:dateTime($b[1]/@dateTime))
                          then "newer" 
                          else "older"}"> 
              {$a[1]}
           </div>,
            local:merge(subsequence($a,2), subsequence($b,2))
           )
   };

The sample data and main script are changed slightly: 

declare option exist:serialize "method=xhtml media-type=text/html";

let $list1 :=
<list>
   <item dateTime="2009-06-01T11:59:00.000-05:00">apples</item>
   <item dateTime="2009-02-01T11:59:00.000-05:00">bananas</item>
   <item dateTime="2009-02-01T11:59:00.000-05:00">carrots</item>
   <item dateTime="2009-02-01T11:59:00.000-05:00">cabbage</item>
   <item dateTime="2009-02-01T11:59:00.000-05:00">eggplant</item>
   <item dateTime="2009-02-01T11:59:00.000-05:00">grapes</item>
 </list>
 
let $list2 :=
<list>
   <item dateTime="2009-01-01T11:59:00.000-05:00">apples</item>
   <item dateTime="2009-02-01T11:59:00.000-05:00">bananas</item>
   <item dateTime="2009-03-01T11:59:00.000-05:00">carrots</item>
   <item dateTime="2009-02-01T11:58:00.000-05:00">eggplant</item>
   <item dateTime="2009-02-01T12:00:00.000-05:00">grapes</item>
   <item dateTime="2009-04-01T11:59:00.000-05:00">oranges</item>
</list>

return

<html>
   <head>
   <style language="text/css">
  <![CDATA[
    body {font-family: Ariel,Helvetica,sans-serif; font-size: medium;}
    h2 {padding: 3px; margin: 0px; text-align: center; font-size: large; background-color: silver;}
    .left, .right {border: solid black 1px; padding: 5px;}
    .newer{background-color: lightgreen;}
    .older{background-color: lightred;}
     .delete{background-color: red;}
    .add{background-color: green;}
   .left {float: left; width: 390px}
    .right {margin-left: 410px; width: 390px}
 
  ]]>
  </style>
 
   </head>
   <body>
      <h1>Update Report</h1>
      <div class="left">
         <h2>List 1</h2>
         {for $item in $list1/item return <div>{$item/text()} dateTime={string($item/@dateTime)}</div>}
      </div>
      <div class="right">
         <h2>List 2</h2>
         {for $item in $list2/item return <div>{fn:current-dateTime} dateTime={string(dateTime(current-dateTime))}</div>}
      </div>
      <br/>
      <p>Green are new, light green are newer and red to be removed</p>
      <div class="left">
         <h2>Merged Lists</h2>
         {local:merge($list1/item, $list2/item)}
      </div>
    </body>
</html>

Execute

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