Comparing two XML files & generating a third with XMLDiff in C#

Question

I am trying to write a simple algorithm to read two XML files with the exact same nodes and structure but not necessarily the same data inside the child nodes and not the same order. How could I create a simple implementation for creating a third, temporary XML being the differential between the two first ones, using Microsoft's XML Diff .DLL ?

XML Diff on MSDN:

XML Diff and Patch Tool

XML Diff and Patch GUI Tool

sample XML code of the two different XML files to compare:

<?xml version="1.0" encoding="utf-8" ?> 
<Stats Date="2011-01-01">
 <Player Rank="1">
  <Name>Sidney Crosby</Name> 
  <Team>PIT</Team> 
  <Pos>C</Pos> 
  <GP>39</GP> 
  <G>32</G> 
  <A>33</A> 
  <PlusMinus>20</PlusMinus> 
  <PIM>29</PIM> 
 </Player>
</Stats>

<?xml version="1.0" encoding="utf-8" ?> 
<Stats Date="2011-01-10">
 <Player Rank="1">
  <Name>Sidney Crosby</Name> 
  <Team>PIT</Team> 
  <Pos>C</Pos> 
  <GP>42</GP> 
  <G>35</G> 
  <A>34</A> 
  <PlusMinus>22</PlusMinus> 
  <PIM>30</PIM> 
 </Player>
</Stats>

Result wanted (difference between the two)

<?xml version="1.0" encoding="utf-8" ?> 
<Stats Date="2011-01-10">
 <Player Rank="1">
  <Name>Sidney Crosby</Name> 
  <Team>PIT</Team> 
  <Pos>C</Pos> 
  <GP>3</GP> 
  <G>3</G> 
  <A>1</A> 
  <PlusMinus>2</PlusMinus> 
  <PIM>1</PIM> 
 </Player>
</Stats>

In this case, I would probably use XSLT to convert the resulting XML "differential" file into a sorted HTML file, but I am not there yet. All I want to do is to display in the third XML file the difference of every numerical value of each nodes, starting from the "GP" child-node.

C# code I have so far:

private void CompareXml(string file1, string file2)
{

    XmlReader reader1 = XmlReader.Create(new StringReader(file1));
    XmlReader reader2 = XmlReader.Create(new StringReader(file2));

    string diffFile = StatsFile.XmlDiffFilename;
    StringBuilder differenceStringBuilder = new StringBuilder();

    FileStream fs = new FileStream(diffFile, FileMode.Create);
    XmlWriter diffGramWriter = XmlWriter.Create(fs);

    XmlDiff xmldiff = new XmlDiff(XmlDiffOptions.IgnoreChildOrder |
                            XmlDiffOptions.IgnoreNamespaces |
                            XmlDiffOptions.IgnorePrefixes);
    bool bIdentical = xmldiff.Compare(file1, file2, false, diffGramWriter);

    diffGramWriter.Close();

    // cleaning up after we are done with the xml diff file
    File.Delete(diffFile);
}

That's what I have so far, but the results is garbage... note that for each "Player" node, the first three childs have NOT to be compared... How can I implement this?

Answer 1

There are two immediate solutions:

Solution 1.

You can first apply a simple transform to the two documents that will delete the elements that should not be compared. Then, compare the results ing two documents -- exactly with your current code. Here is the transformation:

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

 <xsl:template match="node()|@*">
  <xsl:copy>
   <xsl:apply-templates select="node()|@*"/>
  </xsl:copy>
 </xsl:template>

 <xsl:template match="Name|Team|Pos"/>
</xsl:stylesheet>

When this transformation is applied to the provided XML document:

<Stats Date="2011-01-01">
    <Player Rank="1">
        <Name>Sidney Crosby</Name>
        <Team>PIT</Team>
        <Pos>C</Pos>
        <GP>39</GP>
        <G>32</G>
        <A>33</A>
        <PlusMinus>20</PlusMinus>
        <PIM>29</PIM>
        <PP>10</PP>
        <SH>1</SH>
        <GW>3</GW>
        <Shots>0</Shots>
        <ShotPctg>154</ShotPctg>
        <TOIPerGame>20.8</TOIPerGame>
        <ShiftsPerGame>21:54</ShiftsPerGame>
        <FOWinPctg>22.6</FOWinPctg>
    </Player>
</Stats>

the wanted resulting document is produced:

<Stats Date="2011-01-01">
   <Player Rank="1">
      <GP>39</GP>
      <G>32</G>
      <A>33</A>
      <PlusMinus>20</PlusMinus>
      <PIM>29</PIM>
      <PP>10</PP>
      <SH>1</SH>
      <GW>3</GW>
      <Shots>0</Shots>
      <ShotPctg>154</ShotPctg>
      <TOIPerGame>20.8</TOIPerGame>
      <ShiftsPerGame>21:54</ShiftsPerGame>
      <FOWinPctg>22.6</FOWinPctg>
   </Player>
</Stats>

Solution 2.

This is a complete XSLT 1.0 solution (for convenience only, the second XML document is embedded in the transformation code):

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

 <xsl:variable name="vrtfDoc2">
  <Stats Date="2011-01-01">
    <Player Rank="2">
        <Name>John Smith</Name>
        <Team>NY</Team>
        <Pos>D</Pos>
        <GP>38</GP>
        <G>32</G>
        <A>33</A>
        <PlusMinus>15</PlusMinus>
        <PIM>29</PIM>
        <PP>10</PP>
        <SH>1</SH>
        <GW>4</GW>
        <Shots>0</Shots>
        <ShotPctg>158</ShotPctg>
        <TOIPerGame>20.8</TOIPerGame>
        <ShiftsPerGame>21:54</ShiftsPerGame>
        <FOWinPctg>22.6</FOWinPctg>
    </Player>
  </Stats>
 </xsl:variable>

 <xsl:variable name="vDoc2" select=
  "document('')/*/xsl:variable[@name='vrtfDoc2']/*"/>

 <xsl:template match="node()|@*" name="identity">
  <xsl:param name="pDoc2"/>
  <xsl:copy>
   <xsl:apply-templates select="node()|@*">
    <xsl:with-param name="pDoc2" select="$pDoc2"/>
   </xsl:apply-templates>
  </xsl:copy>
 </xsl:template>

 <xsl:template match="/">
  <xsl:apply-templates select="*">
   <xsl:with-param name="pDoc2" select="$vDoc2"/>
  </xsl:apply-templates>

  -----------------------

  <xsl:apply-templates select="$vDoc2">
   <xsl:with-param name="pDoc2" select="/*"/>
  </xsl:apply-templates>
 </xsl:template>

 <xsl:template match="Player/*">
  <xsl:param name="pDoc2"/>
  <xsl:if test=
   "not(. = $pDoc2/*/*[name()=name(current())])">
   <xsl:call-template name="identity"/>
  </xsl:if>
 </xsl:template>

 <xsl:template match="Name|Team|Pos" priority="20"/>
</xsl:stylesheet>

when this transformation is applied on the same first document as above, the correct diffgrams are produced:

<Stats Date="2011-01-01">
   <Player Rank="1">
      <GP>39</GP>
      <PlusMinus>20</PlusMinus>
      <GW>3</GW>
      <ShotPctg>154</ShotPctg>
   </Player>
</Stats>

  -----------------------

  <Stats xmlns:xsl="http://www.w3.org/1999/XSL/Transform" Date="2011-01-01">
   <Player Rank="2">
      <GP>38</GP>
      <PlusMinus>15</PlusMinus>
      <GW>4</GW>
      <ShotPctg>158</ShotPctg>
   </Player>
</Stats>

How this works:

1. The transformation is applied on the first document, passing the second document as parameter.

2. This produces an XML document whose only leaf element nodes are the ones that have different value than the corresponding leaf element nodes in the second document.

3. The same processing is performed as in 1. above, but this time on the second document, passing the first document as parameter.

4. This produces a second diffgram: an XML document whose only leaf element nodes are the ones that have different value** than the corresponding leaf element nodes in the first document