在XPath查询特殊字符 [英] Special Character in XPATH Query

问题描述

我用下面的 XPath查询来列出站点下的对象。 的ListObject [@标题=someValue中'] 。 someValue中是动态的。该查询只要someValue中没有一个单引号（'）的作品。使用转义序列也尝试过。没有工作。

I use the following XPATH Query to list the object under a site. ListObject[@Title='SomeValue']. SomeValue is dynamic. This query works as long as SomeValue does not have an apostrophe ('). Tried using escape sequence also. Didn't work.

我在做什么错了？

推荐答案

这是相当困难的事情。

看看在的XPath建议，你会看到，它定义了一个文本为：

Take a look at theXPath Recommendation, and you'll see that it defines a literal as:

Literal ::=   '"' [^"]* '"' 
            | "'" [^']* "'"

这就是说，在XPath的前pressions字符串可以包含撇号或双引号，但不能同时使用。

Which is to say, string literals in XPath expressions can contain apostrophes or double quotes but not both.

您不能使用转义来解决这个问题。字面上是这样的：

You can't use escaping to get around this. A literal like this:

'Some'Value'

将匹配这个XML文本：

will match this XML text:

Some'Value

这并不意味着它是有可能存在是一块XML文本，你不能生成一个XPath字面匹配，例如：

This does mean that it's possible for there to be a piece of XML text that you can't generate an XPath literal to match, e.g.:

<elm att="&quot;&apos"/>

但是，这并不意味着它是不可能的使用XPath的文本匹配，它只是棘手。当你想匹配的值中包含单引号和双引号的情况下，可以构造一个使用前pression CONCAT 来生产它的文本要匹配：

But that doesn't mean it's impossible to match that text with XPath, it's just tricky. In any case where the value you're trying to match contains both single and double quotes, you can construct an expression that uses concat to produce the text that it's going to match:

elm[@att=concat('"', "'")]

所以这导致我们这一点，这是一个复杂得多比我想它是：

So that leads us to this, which is a lot more complicated than I'd like it to be:

/// <summary>
/// Produce an XPath literal equal to the value if possible; if not, produce
/// an XPath expression that will match the value.
/// 
/// Note that this function will produce very long XPath expressions if a value
/// contains a long run of double quotes.
/// </summary>
/// <param name="value">The value to match.</param>
/// <returns>If the value contains only single or double quotes, an XPath
/// literal equal to the value.  If it contains both, an XPath expression,
/// using concat(), that evaluates to the value.</returns>
static string XPathLiteral(string value)
{
    // if the value contains only single or double quotes, construct
    // an XPath literal
    if (!value.Contains("\""))
    {
        return "\"" + value + "\"";
    }
    if (!value.Contains("'"))
    {
        return "'" + value + "'";
    }

    // if the value contains both single and double quotes, construct an
    // expression that concatenates all non-double-quote substrings with
    // the quotes, e.g.:
    //
    //    concat("foo", '"', "bar")
    StringBuilder sb = new StringBuilder();
    sb.Append("concat(");
    string[] substrings = value.Split('\"');
    for (int i = 0; i < substrings.Length; i++ )
    {
        bool needComma = (i>0);
        if (substrings[i] != "")
        {
            if (i > 0)
            {
                sb.Append(", ");
            }
            sb.Append("\"");
            sb.Append(substrings[i]);
            sb.Append("\"");
            needComma = true;
        }
        if (i < substrings.Length - 1)
        {
            if (needComma)
            {
                sb.Append(", ");                    
            }
            sb.Append("'\"'");
        }

    }
    sb.Append(")");
    return sb.ToString();
}

是的，我所有的边缘情况进行了测试。这就是为什么逻辑是如此愚蠢复杂的：

And yes, I tested it with all the edge cases. That's why the logic is so stupidly complex:

    foreach (string s in new[]
    {
        "foo",              // no quotes
        "\"foo",            // double quotes only
        "'foo",             // single quotes only
        "'foo\"bar",        // both; double quotes in mid-string
        "'foo\"bar\"baz",   // multiple double quotes in mid-string
        "'foo\"",           // string ends with double quotes
        "'foo\"\"",         // string ends with run of double quotes
        "\"'foo",           // string begins with double quotes
        "\"\"'foo",         // string begins with run of double quotes
        "'foo\"\"bar"       // run of double quotes in mid-string
    })
    {
        Console.Write(s);
        Console.Write(" = ");
        Console.WriteLine(XPathLiteral(s));
        XmlElement elm = d.CreateElement("test");
        d.DocumentElement.AppendChild(elm);
        elm.SetAttribute("value", s);

        string xpath = "/root/test[@value = " + XPathLiteral(s) + "]";
        if (d.SelectSingleNode(xpath) == elm)
        {
            Console.WriteLine("OK");
        }
        else
        {
            Console.WriteLine("Should have found a match for {0}, and didn't.", s);
        }
    }
    Console.ReadKey();
}

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