Saxon扩展:XdmNode上的XPath

Question

嗨，我试图在C#中实现saxon的扩展。我使用saxon9he接口。扩展本身运行良好，但现在我想使用XPath表达式从节点获取值。我将其分解为相关的代码部分(其余部分工作正常)。

扩展名有两个参数。第一个是字符串，第二个是节点集。

public override IXdmEnumerator Call(IXdmEnumerator[] arguments, DynamicContext context)
{
if (arguments.Length == 2)
{
arguments[0].MoveNext();
string text = (arguments[0].Current as XdmAtomicValue).Value as string;
IXdmEnumerator enumerator = arguments[1];
while (enumerator.MoveNext())
{
XdmNode node = (XdmNode)enumerator.Current;
// how can I get values from node here by using XPath expressions?
// e.g. I want the value of the attribute "type" of the subnode "xy"
// XPath would be something like this: "./xy/@type"
text = text.Replace(node.NodeName.LocalName, node.StringValue);
}
var result = new XdmAtomicValue(text);
return (IXdmEnumerator)result.GetEnumerator();
}
...
}

中间的3条评论说明了我的问题。我想通过XPath表达式访问子节点、属性等。这是一个简化版本。XPath应稍后作为附加参数传递。因此，它不是一个可以转换为代码的固定XPath表达式。我真的需要一个XPath计算器。

我看到了一个从处理器创建XPathEvaluator的解决方案。但我现在没有处理器，还是我没有？

谢谢你的帮助。

以下是解决方案(感谢Michael)：

var configuration = context.Implementation.getConfiguration();
var processor = (Processor)configuration.getProcessor();
var xpathCompiler = processor.NewXPathCompiler();
while (enumerator.MoveNext())
{
XdmNode node = (XdmNode)enumerator.Current;
var keyResult = xpathCompiler.Evaluate(searchXPath, node);
var valueResult = xpathCompiler.Evaluate(replaceXPath, node);
string key = "";
string value = "";
if (keyResult is XdmAtomicValue)
key = (string)(keyResult as XdmAtomicValue).Value;
else if (keyResult is XdmNode)
key = (string)(keyResult as XdmNode).StringValue;
if (valueResult is XdmAtomicValue)
value = (string)(valueResult as XdmAtomicValue).Value;
else if (valueResult is XdmNode)
value = (string)(valueResult as XdmNode).StringValue;
if (string.IsNullOrWhiteSpace(key) || value == null)
continue;
text = text.Replace(key, value);
}

Saxon 9.7的解决方案：

上面的解决方案不再适用于Saxon 9.7。在这种情况下，我将处理器传递给扩展类，并在注册扩展时从那里传递给扩展调用类。

public static void RegisterSaxonExtensions(Saxon.Api.Processor processor)
{
processor.RegisterExtensionFunction(new MyExtension1(processor));
processor.RegisterExtensionFunction(new MyExtension2(processor));
}
...
public class MyExtension1 : Saxon.Api.ExtensionFunctionDefinition
{
private Saxon.Api.Processor processor = null;
public MyExtension1(Saxon.Api.Processor processor)
{
this.processor = processor;
}
public override ExtensionFunctionCall MakeFunctionCall()
{
return new MyExtension1Call(this.processor);
}
...
}
public class MyExtension1Call : Saxon.Api.ExtensionFunctionCall
{
private Saxon.Api.Processor processor = null;
public MyExtension1Call(Saxon.Api.Processor processor)
{
this.processor = processor;
}
public override IXdmEnumerator Call(IXdmEnumerator[] arguments, DynamicContext context)
{
if (arguments.Length == 2)
{
arguments[0].MoveNext();
string text = (arguments[0].Current as XdmAtomicValue).Value as string;
IXdmEnumerator enumerator = arguments[1];
var xpathCompiler = this.processor.NewXPathCompiler();
while (enumerator.MoveNext())
{
XdmNode node = (XdmNode)enumerator.Current;
var keyResult = xpathCompiler.Evaluate(searchXPath, node);
var valueResult = xpathCompiler.Evaluate(replaceXPath, node);
string key = "";
string value = "";
if (keyResult is XdmAtomicValue)
key = (string)(keyResult as XdmAtomicValue).Value;
else if (keyResult is XdmNode)
key = (string)(keyResult as XdmNode).StringValue;
if (valueResult is XdmAtomicValue)
value = (string)(valueResult as XdmAtomicValue).Value;
else if (valueResult is XdmNode)
value = (string)(valueResult as XdmNode).StringValue;
if (string.IsNullOrWhiteSpace(key) || value == null)
continue;
text = text.Replace(key, value);
}
var result = new XdmAtomicValue(text);
return (IXdmEnumerator)result.GetEnumerator();
}
}
}

Answer 1

DynamicContext.Iimplementation为您提供了一个XPathContext对象，它有一个getConfiguration()方法来获取Configuration，Processor对象应该在Configuration.getProcessor()中找到。从中您应该能够创建一个XPath Evaluator。