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POWhy is XmlNamespaceManager necessary?
 

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    <p>I've come up kinda dry as to <strong>why</strong> -- at least in the .Net Framework -- it is necessary to use an <code>XmlNamespaceManager</code> in order to handle namespaces (or the rather clunky and verbose <code>[local-name()=...</code> XPath predicate/function/whatever) when performing XPath queries. I <strong>do</strong> understand why namespaces are necessary or at least beneficial, but <strong>why</strong> is it so complex?</p> <p>In order to query a simple XML Document (no namespaces)...</p> <pre><code>&lt;?xml version="1.0" encoding="ISO-8859-1"?&gt; &lt;rootNode&gt; &lt;nodeName&gt;Some Text Here&lt;/nodeName&gt; &lt;/rootNode&gt; </code></pre> <p>...one can use something like <code>doc.SelectSingleNode("//nodeName")</code> (which would match <code>&lt;nodeName&gt;Some Text Here&lt;/nodeName&gt;</code>)</p> <p><em>Mystery #1</em>: <strong>My first annoyance</strong> -- If I understand correctly -- is that merely adding a namespace reference to the parent/root tag (whether used as part of a child node tag or not) like so:</p> <pre><code>&lt;?xml version="1.0" encoding="ISO-8859-1"?&gt; &lt;rootNode xmlns="http://someplace.org"&gt; &lt;nodeName&gt;Some Text Here&lt;/nodeName&gt; &lt;/rootNode&gt; </code></pre> <p>...requires several extra lines of code to get the same result:</p> <pre><code>Dim nsmgr As New XmlNamespaceManager(doc.NameTable) nsmgr.AddNamespace("ab", "http://s+omeplace.org") Dim desiredNode As XmlNode = doc.SelectSingleNode("//ab:nodeName", nsmgr) </code></pre> <p>...essentially dreaming up a non-existent prefix ("<code>ab</code>") to find a node that doesn't even use a prefix. <em>How does this make sense?</em> What is wrong (conceptually) with <code>doc.SelectSingleNode("//nodeName")</code>?</p> <p><em>Mystery #2</em>: So, say you've got an XML document that uses prefixes:</p> <pre><code>&lt;?xml version="1.0" encoding="ISO-8859-1"?&gt; &lt;rootNode xmlns:cde="http://someplace.org" xmlns:feg="http://otherplace.net"&gt; &lt;cde:nodeName&gt;Some Text Here&lt;/cde:nodeName&gt; &lt;feg:nodeName&gt;Some Other Value&lt;/feg:nodeName&gt; &lt;feg:otherName&gt;Yet Another Value&lt;/feg:otherName&gt; &lt;/rootNode&gt; </code></pre> <p>... If I understand correctly, you would have to add both namespaces to the <code>XmlNamespaceManager</code>, in order to make a query for a single node...</p> <pre><code>Dim nsmgr As New XmlNamespaceManager(doc.NameTable) nsmgr.AddNamespace("cde", "http://someplace.org") nsmgr.AddNamespace("feg", "http://otherplace.net") Dim desiredNode As XmlNode = doc.SelectSingleNode("//feg:nodeName", nsmgr) </code></pre> <p>... Why, in this case, do I need (conceptually) a namespace manager? </p> <p><em><strong></em>**REDACTED into comments below**</strong></p> <p><strong>Edit Added:</strong> My revised and refined question is based upon the apparent redundancy of the XmlNamespaceManager in what I believe to be the majority of cases and the use of the namespace manager to specify a mapping of prefix to URI:</p> <p>When the direct mapping of the namespace prefix ("cde") to the namespace URI ("http://someplace.org") is explicitly stated in the source document: </p> <pre><code>...&lt;rootNode xmlns:cde="http://someplace.org"... </code></pre> <p>what is the conceptual need for a programmer to recreate that mapping before making a query?</p>
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    1. COAs a quick addendum, I concede there are probably situations where something like an XMLNamespaceManager would make things easier, but I believe in the above situations it makes things CONSIDERABLY harder than they have to be.
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    2. COMy primary source of confusion is why the relationship of prefix to namespace needs to be specified BOTH in the XML document and the code that implements the XPath Query. If the root node contains the mapping already, why do I have to essentially hard code information that is already parsed when the document is loaded? Also, if a third namespace is added to the document in the future, would I not have to alter and recompile my code to declare that third relationship?
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    3. CO**REDACTED from above:** What is wrong with simply putting the namespace prefix in the XPath query --`doc.SelectSingleNode("//feg:nodeName")` -- and being done with it? To the human brain, can there be any doubt as to what is meant by that code fragment? _[PARAGRAPH]_ Stated differently, what is really added to the understanding of the situation by the extra lines of code and the instantiation of an XmlNamespaceManager that is not clearly derivable from the source XML document and/or the XPath Query?
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