Вывод уникальных значений атрибута XSLT при использовании ключа, вложенного в другой ключ

Я работал над веб-страницей, созданной с помощью комбинации XSLT 1.0 и XML, и столкнулся с проблемой, когда я изо всех сил пытался экспортировать уникальные значения атрибутов при использовании < href="http://www.w3schools.com/xsl/el_key.asp" rel="nofollow">XSL-ключ (<xsl:keyname="name" match="pattern" use="expression"/>), вложенный в другой XSL-ключ.

Из-за чувствительности моих XML-данных я реконструировал свою проблему, точно используя «классический пример W3C Schools» книжного магазина.

Код:

XSL:

<xsl:stylesheet
  version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:output indent="yes"/>

<xsl:key name="prom-by-id" match="bookstore/promotion" use="promotionID"/>
<xsl:key name="location-by-id" match="bookstore/locations" use="locationID"/>

<xsl:template match="bookstore">
  <xsl:apply-templates select="book"/>
</xsl:template>

<xsl:template match="book">
  <xsl:copy>
     <p><strong><xsl:value-of select="title"/></strong></p>
          <xsl:for-each select="key('prom-by-id', occurrences/promotions/promotionNum)">
            <xsl:for-each select="key('location-by-id', promotionLocation)">
              <p><xsl:value-of select="location"/></p>
            </xsl:for-each>
          </xsl:for-each>
     <br/><br/>
   </xsl:copy>
</xsl:template>

XML:

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="books.xsl" ?>
<bookstore>
  <book>
    <title>Harry Potter and the Philosopher's Stone</title>
    <author>J K. Rowling</author>
    <year>1997</year>
    <price>3.99</price>
    <publisher>Bloomsbury (UK)</publisher>
    <synopsis>
         Harry Potter and the Philosopher's Stone is the first novel in the Harry Potter series and J. K. Rowling's debut novel.

         The plot follows Harry Potter, a young wizard who discovers his magical heritage as he makes close friends and a few enemies in his first year at the Hogwarts School of Witchcraft and Wizardry.

         With the help of his friends, Harry faces an attempted comeback by the dark wizard Lord Voldemort, who killed Harry's parents, but failed to kill Harry when he was just a year old.
   </synopsis>
   <occurrences>
    <promotions>
      <promotionCode>1</promotionCode>
      <promotionNum>1</promotionNum>
      <promotionNum>2</promotionNum>
      <promotionNum>3</promotionNum>
      <promotionNum>4</promotionNum>
   </promotions>
   </occurrences>
 </book>
 <book>
    <title>The Girl with the Dragon Tattoo</title>
    <author>Stieg Larsson</author>
    <year>2005</year>
    <price>5.99</price>
    <publisher>Norstedts Förlag (SWE)</publisher>
    <synopsis>
         In Stockholm, Sweden, journalist Mikael Blomkvist, co-owner of Millennium magazine, has lost a libel case brought against him by businessman Hans-Erik Wennerström. Lisbeth Salander, a brilliant but troubled investigator and hacker, compiles an extensive background check on Blomkvist for business magnate Henrik Vanger, who has a special task for him. 

         In exchange for the promise of damning information about Wennerström, Blomkvist agrees to investigate the disappearance and assumed murder of Henrik's grandniece, Harriet, 40 years ago. 

         After moving to the Vanger family's compound, Blomkvist uncovers a notebook containing a list of names and numbers that no one has been able to decipher.
    </synopsis>
    <occurrences>
      <promotions>
         <promotionCode>3</promotionCode>
        <promotionNum>5</promotionNum>
        <promotionNum>6</promotionNum>
        <promotionNum>3</promotionNum>
        <promotionNum>2</promotionNum>
      </promotions>
    </occurrences>
  </book>
   <book>
    <title>Grandpa's Great Escape</title>
    <author>David Walliams</author>
    <year>2015</year>
    <price>5.00</price>
    <publisher>Harper Collins Children's Books</publisher>
    <synopsis>
         An exquisite portrait of the bond between a small boy and his beloved Grandpa – this book takes readers on an incredible journey with Spitfires over London and Great Escapes through the city in a high octane adventure full of comedy and heart. Illustrated by the award-winning Tony Ross.
    </synopsis>
    <occurrences>
    <promotions>
      <promotionCode>4</promotionCode>
      <promotionNum>1</promotionNum>
      <promotionNum>2</promotionNum>
      <promotionNum>4</promotionNum>
   </promotions>
 </occurrences>
  </book>
<book>
    <title>A Brief History of Seven Killings</title>
    <author>Marlon James</author>
    <year>2015</year>
    <price>6.29</price>
    <publisher>Oneworld Publications</publisher>
    <synopsis>
         From the acclaimed author of The Book of Night Women comes a dazzling display of masterful storytelling exploring this near-mythic event. Spanning three decades and crossing continents, A Brief History of Seven Killings chronicles the lives of a host of unforgettable characters – slum kids, one-night stands, drug lords, girlfriends, gunmen, journalists, and even the CIA. 

         Gripping and inventive, ambitious and mesmerising, A Brief History of Seven Killings is one of the most remarkable and extraordinary novels of the twenty-first century.
    </synopsis>
    <occurrences>
      <promotions>
         <promotionCode>5</promotionCode>
        <promotionNum>1</promotionNum>
        <promotionNum>5</promotionNum>
        <promotionNum>6</promotionNum>
      </promotions>
    </occurrences>
        <occurrences>
      <promotions>
         <promotionCode>5</promotionCode>
        <promotionNum>1</promotionNum>
        <promotionNum>5</promotionNum>
        <promotionNum>6</promotionNum>
      </promotions>
    </occurrences>
  </book>
  <book>
    <title>Leading</title>
    <author>Sir Alex Ferguson</author>
    <year>2015</year>
    <price>7.99</price>
    <publisher>Hodder and Stoughton</publisher>
    <synopsis>
         In this revelatory new book, Sir Alex Ferguson dissects his 38 record-breaking years of management - first in Scotland and then, of course, at Manchester United - to reveal the key tools he used to deliver sustained success on and off the field. From tactics to teamwork, from hiring to firing, from dealing with the boardroom to responding to failure, LEADING investigates the pivotal leadership decisions of an astonishing career.
    </synopsis>
    <occurrences>
      <promotions>
         <promotionCode>6</promotionCode>
        <promotionNum>2</promotionNum>
        <promotionNum>3</promotionNum>
        <promotionNum>6</promotionNum>
      </promotions>
    </occurrences>
  </book>
  <book>
    <title>The Girl on the Train</title>
    <author>Paula Hawkins</author>
    <year>2015</year>
    <price>6.99</price>
    <publisher>Doubleday</publisher>
    <synopsis>
         Rachel catches the same commuter train every morning. She knows it will wait at the same signal each time, overlooking a row of back gardens. She’s even started to feel like she knows the people who live in one of the houses. ‘Jess and Jason’, she calls them. Their life – as she sees it – is perfect. If only Rachel could be that happy.

        And then she sees something shocking. It’s only a minute until the train moves on, but it’s enough. 

        Now everything’s changed. Now Rachel has a chance to become a part of the lives she’s only watched from afar.

        Now they’ll see; she’s much more than just the girl on the train…
    </synopsis>
    <occurrences>
      <promotions>
         <promotionCode>7</promotionCode>
        <promotionNum>1</promotionNum>
        <promotionNum>2</promotionNum>
        <promotionNum>3</promotionNum>
        <promotionNum>4</promotionNum>
      </promotions>
    </occurrences>
  </book>

  <promotion>
    <promotionID>1</promotionID>
    <percentageOff>10</percentageOff>
    <promotionalMerchandise>No</promotionalMerchandise>
    <promotionStartDate>2015-10-14T00:00:00</promotionStartDate>
    <promotionEndDate>2015-10-19T00:00:00</promotionEndDate>
    <promotionLocation>1</promotionLocation>
  </promotion>
  <promotion>
    <promotionID>2</promotionID>
    <percentageOff>15</percentageOff>
    <promotionalMerchandise>No</promotionalMerchandise>
    <promotionStartDate>2015-10-11T00:00:00</promotionStartDate>
    <promotionEndDate>2015-10-16T00:00:00</promotionEndDate>
    <promotionLocation>2</promotionLocation>
  </promotion>
  <promotion>
    <promotionID>3</promotionID>
    <percentageOff>30</percentageOff>
    <promotionalMerchandise>Yes</promotionalMerchandise>
    <promotionStartDate>2015-09-02T00:00:00</promotionStartDate>
    <promotionEndDate>2015-09-07T00:00:00</promotionEndDate>
    <promotionLocation>2</promotionLocation>
  </promotion>
  <promotion>
    <promotionID>4</promotionID>
    <percentageOff>5</percentageOff>
    <promotionalMerchandise>Yes</promotionalMerchandise>
    <promotionStartDate>2015-11-22T00:00:00</promotionStartDate>
    <promotionEndDate>2015-11-27T00:00:00</promotionEndDate>
    <promotionLocation>3</promotionLocation>
  </promotion>
  <promotion>
    <promotionID>5</promotionID>
    <percentageOff>50</percentageOff>
    <promotionalMerchandise>No</promotionalMerchandise>
    <promotionStartDate>2015-08-13T00:00:00</promotionStartDate>
    <promotionEndDate>2015-08-18T00:00:00</promotionEndDate>
    <promotionLocation>1</promotionLocation>
  </promotion>
  <promotion>
    <promotionID>6</promotionID>
    <percentageOff>80</percentageOff>
    <promotionalMerchandise>No</promotionalMerchandise>
    <promotionStartDate>2015-07-01T00:00:00</promotionStartDate>
    <promotionEndDate>2015-07-05T00:00:00</promotionEndDate>
    <promotionLocation>1</promotionLocation>
  </promotion>

  <locations>
    <locationID>1</locationID>
    <location>York</location>
  </locations>
    <locations>
      <locationID>2</locationID>
    <location>London</location>
  </locations>
    <locations>
      <locationID>3</locationID>
    <location>Glasgow</location>
  </locations>
</bookstore>

Живой пример:

Я создал живую версию этой задачи, которую можно посмотреть на @ http://xsltransform.net/94rmq6J.

Проблема:

Часть первая

Для каждого атрибута <book/occurrences>, хранящегося в моих XML-данных, я использую свой первый <xsl:key> для перекрестной ссылки на каждое доступное значение <book/occurrences/promotionNum> (число) с любым соответствующим значением <bookstore/promotion/promotionID>.

Часть вторая

Если найдено совпадение <bookstore/promotion/promotionID>, то запускается второе <xsl:key> с таргетингом на <bookstore/promotion/promotionLocation> в качестве критерия поиска, и это пытается окончательно найти любое значение <bookstore/locations/locationID>.

Часть третья

Если выполняется второе и последнее совпадение, то выводится значение <bookstore/locations/location>, предоставляющее название города в Великобритании.

К сожалению, я изо всех сил пытаюсь найти способ вывести уникальные значения <bookstore/locations/location>, когда города часто повторяются два или три раза за <book/occurrences>.

Фактический вывод:

<book>
   <p>
      <strong>Harry Potter and the Philosopher's Stone</strong>
   </p>
   <p>York</p>
   <p>London</p>
   <p>London</p>
   <p>Glasgow</p>
   <p>York</p>
   <br/>
   <br/>
</book>
<book>
   <p>
      <strong>The Girl with the Dragon Tattoo</strong>
   </p>
   <p>London</p>
   <p>London</p>
   <p>York</p>
   <p>York</p>
   <br/>
   <br/>
</book>
<book>
   <p>
      <strong>Grandpa's Great Escape</strong>
   </p>
   <p>York</p>
   <p>London</p>
   <p>Glasgow</p>
   <br/>
   <br/>
</book>
<book>
   <p>
      <strong>A Brief History of Seven Killings</strong>
   </p>
   <p>York</p>
   <p>York</p>
   <p>York</p>
   <br/>
   <br/>
</book>
<book>
   <p>
      <strong>Leading</strong>
   </p>
   <p>London</p>
   <p>London</p>
   <p>York</p>
   <br/>
   <br/>
</book>
<book>
   <p>
      <strong>The Girl on the Train</strong>
   </p>
   <p>York</p>
   <p>London</p>
   <p>London</p>
   <p>Glasgow</p>
   <br/>
   <br/>
</book>

Желаемый результат:

<book>
   <p>
      <strong>Harry Potter and the Philosopher's Stone</strong>
   </p>
   <p>York</p>
   <p>London</p>
   <p>Glasgow</p>
   <br/>
   <br/>
</book>
<book>
   <p>
      <strong>The Girl with the Dragon Tattoo</strong>
   </p>
   <p>London</p>
   <p>York</p>
   <br/>
   <br/>
</book>
<book>
   <p>
      <strong>Grandpa's Great Escape</strong>
   </p>
   <p>York</p>
   <p>London</p>
   <p>Glasgow</p>
   <br/>
   <br/>
</book>
<book>
   <p>
      <strong>A Brief History of Seven Killings</strong>
   </p>
   <p>York</p>
   <br/>
   <br/>
</book>
<book>
   <p>
      <strong>Leading</strong>
   </p>
   <p>London</p>
   <p>York</p>
   <br/>
   <br/>
</book>
<book>
   <p>
      <strong>The Girl on the Train</strong>
   </p>
   <p>York</p>
   <p>London</p>
   <p>Glasgow</p>
   <br/>
   <br/>
</book>

Итак, что я могу сделать, чтобы решить эту проблему? Относится ли это к preceding-sibling или preceding в моем <xsl:key> или будет работать мюнхенский метод? , используя некоторую форму generate-id на <book/occurrences/promotionNum>? Я уверен, что это одно из этих трех решений, но я не уверен, какое?

Любая помощь будет принята с благодарностью заранее.