/// <summary>
/// Compile and execute an expression supplied as a <c>String</c>, with a given context item, where
/// the expression is expected to return a single item as its result.
/// </summary>
/// <param name="expression">A string containing the source text of the XPath expression</param>
/// <param name="contextItem">The context item to be used for evaluation of the XPath expression.
/// May be null, in which case the expression is evaluated without any context item.</param>
/// <returns>If the XPath expression returns a singleton, then the the <c>XdmItem</c>
/// which is the result of evaluating the XPath expression. If the expression returns an empty sequence,
/// then null. If the expression returns a sequence containing more than one item, then the first
/// item in the result.</returns>
/// <exception cref="StaticError">
/// Throws a <c>Saxon.Api.StaticError</c> if there is any static error in the XPath expression.
/// This includes both syntax errors, semantic errors such as references to undeclared functions or
/// variables, and statically-detected type errors.
/// </exception>
/// <exception cref="DynamicError">
/// Throws a <c>Saxon.Api.DynamicError</c> if there is any dynamic error during evaluation of the XPath expression.
/// This includes, for example, referring to the context item if no context item was supplied.
/// </exception>
public XdmItem EvaluateSingle(String expression, XdmItem contextItem)
{
try
{
JXdmItem value = compiler.evaluateSingle(expression, contextItem == null ? null : XdmItem.FromXdmItemItemToJXdmItem(contextItem));
return(value == null ? null : (XdmItem)XdmValue.Wrap(value.getUnderlyingValue()));
}
catch (JSaxonApiException err)
{
if (err.getCause() is JXPathException)
{
JXPathException xpathException = (JXPathException)err.getCause();
if (xpathException.isStaticError())
{
throw new StaticError(err);
}
else
{
throw new DynamicError(err.getMessage());
}
}
else
{
throw new StaticError(err);
}
}
}
/// <summary>
/// Evaluate the XPath expression, returning the result as an <c>XdmItem</c> (that is,
/// a single node or atomic value).
/// </summary>
/// <returns>
/// An <c>XdmItem</c> representing the result of the expression, or null if the expression
/// returns an empty sequence. If the expression returns a sequence of more than one item,
/// any items after the first are ignored.
/// </returns>
/// <exception cref="DynamicError">
/// Throws <c>Saxon.Api.DynamicError</c> if the evaluation of the XPath expression fails
/// with a dynamic error.
/// </exception>
public XdmItem EvaluateSingle()
{
try
{
JXdmItem item = selector.evaluateSingle();
return(item == null ? null : (XdmItem)XdmValue.Wrap(item.getUnderlyingValue().materialize()));
}
catch (JSaxonApiException err)
{
throw new DynamicError(err);
}
}
