Filter XML based on another xml using XSLT 1

Question

How do we filter an xml document based on another xml document. I have to remove all the elements which are not there in the lookup xml. Both the input xml and lookup xml has the same root elements, we are using XSLT 1.0.

Ex Input

<Root>
    <E1 a="1">V1</E1>
    <E2>V2</E2>
    <E3>V3</E3>
    <E5>
       <SE51>SEV1</SE51> 
       <SE52>SEV2</SE52> 
    </E5>
    <E6>
       <SE61>SEV3</SE61> 
       <SE62>SEV4</SE62> 
    </E6>
</Root>

Filter Xml

<Root>
    <E1 a="1"></E1>
    <E2></E2>
    <E5>
       <SE51></SE51> 
       <SE52></SE52> 
    </E5>
</Root>

Expected Output

<Root>
    <E1 a="1">V1</E1>
    <E2>V2</E2>
    <E5>
       <SE51>SEv1</SE51> 
       <SE52>SEV2</SE52> 
    </E5>
</Root>

Answer 1

Hmmm, you're sort of talking about merging (assuming your filter doc is variable). There's a couple of possibilities which vary with the language you're implementing all of this in. Could you provide more info about the app?

Otherwise I suggest a quick google on "xslt +merge" and see if some result there grabs you.

Answer 2

Based on what I've done in the past when faced with similar problems I'd suggest:

• Write a transformation in XSLT to which consumed the "filter XML" and produce a transformation (also in XSLT).
• Run the resulting XSLT on your input.

It sounds (and is) ugly, but I've found this easier than trying to interpret the filter description on the fly while transforming the input.

Answer 3

Here is the required transformation:

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
 xmlns:z="inline:text.xml"
 exclude-result-prefixes="z"
 >
    <xsl:output omit-xml-declaration="yes" indent="yes"/>
    <xsl:strip-space elements="*"/>

    <z:filter>
     <Root>
      <E1 a="1"></E1>
      <E2></E2>
      <E5>
       <SE51></SE51>
       <SE52></SE52>
      </E5>
     </Root>
    </z:filter>

    <xsl:variable name="vFilter" select=
     "document('')/*/z:filter"/>

    <xsl:template match="/">
      <xsl:apply-templates select="*[name()=name($vFilter/*)]">
        <xsl:with-param name="pFiltNode" select="$vFilter/*"/>
      </xsl:apply-templates>
    </xsl:template>

    <xsl:template match="*">
      <xsl:param name="pFiltNode"/>

      <xsl:copy>
       <xsl:copy-of select="@*"/>

       <xsl:for-each select="text() | *">
         <xsl:choose>
           <xsl:when test="self::text()">
             <xsl:copy-of select="."/>
           </xsl:when>
           <xsl:otherwise>
            <xsl:variable name="vFiltNode"
                 select="$pFiltNode/*[name()=name(current())]"/>

            <xsl:apply-templates select="self::node()[$vFiltNode]">
              <xsl:with-param name="pFiltNode" select="$vFiltNode"/>
            </xsl:apply-templates>
           </xsl:otherwise>
         </xsl:choose>
       </xsl:for-each>
      </xsl:copy>
    </xsl:template>
</xsl:stylesheet>

When this transformation is applied on the following XML document (the original one plus the addition of <SE511>SEV11</SE511> to demonstrate that the filtering works on any level:

<Root>
    <E1 a="1">V1</E1>
    <E2>V2</E2>
    <E3>V3</E3>
    <E5>
     <SE51>SEV1</SE51>
     <SE511>SEV11</SE511>
     <SE52>SEV2</SE52>
    </E5>
    <E6>
     <SE61>SEV3</SE61>
     <SE62>SEV4</SE62>
    </E6>
</Root>

the wanted result is produced:

<Root>
    <E1 a="1">V1</E1>
    <E2>V2</E2>
    <E3>V3</E3>
    <E5>
     <SE51>SEV1</SE51>
     <SE511>SEV11</SE511>
     <SE52>SEV2</SE52>
    </E5>
    <E6>
     <SE61>SEV3</SE61>
     <SE62>SEV4</SE62>
    </E6>
</Root>

Do notice the following details of this solution:

1. Templates are applied only to elements that have a matching node in the filter-document and also to all text nodes of such elements.
2. The template that matches an element is passed as parameter the corresponding node in the filter-document.
3. When applying templates to an element-child, its corresponding node is found and passed as the expected parameter.

Do enjoy!