Saxon 扩展：XdmNode 上的 XPath

Question

您好，我尝试在 C# 中实现 saxon 的扩展。我使用 saxon9he 界面。扩展本身工作正常，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 个 cmets 显示了我的问题。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 应该稍后作为附加参数传递。所以它不是我可以转换为代码的固定 XPath 表达式。我真的需要一个 XPath 求值器。

我看到了通过从处理器创建 XPathEvaluator 的解决方案。但是我现在没有处理器，或者我没有？

感谢您的帮助。

这是解决方案（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：

上述解决方案不再适用于 Saxon 9.7。在这种情况下，我在注册扩展时将处理器传递给扩展类并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.Implementation 给你一个 XPathContext 对象，它有一个 getConfiguration() 方法来获取配置，处理器对象应该在 Configuration.getProcessor() 中找到。从中您应该能够创建一个 XPathEvaluator。