在C#中使用Regex替换时忽略字符串引号内的匹配项

问题背景 #

我负责的应用中，系统管理员可创建自定义字段并配置VB.NET语法的计算表达式，这些表达式以字符串形式存储在CustomField对象中。现需批量清理这些表达式，将非短路的函数和运算符替换为短路版本，使用.NET C#的Regex.Replace()实现。

替换需求 #

• 替换规则：IIF → IF，And → AndAlso，Or → OrElse
• 匹配忽略大小写，适配管理员输入的大小写不统一语法
• IIF函数需匹配两种格式：IIF( 和 IIF 后跟任意空白字符再跟 (
• And/Or运算符仅匹配前后带空格的实例，且禁止替换字符串引号内的对应内容

初始方案的局限 #

最初的代码能正确处理IIF的匹配，但无法区分引号内外的And/Or，会误替换字符串中的and/or，不符合需求。

初始代码：

foreach (CustomFieldInfo customField in Session.ConfigurationManager.GetCustomFields(false))
{
    string fieldCalcStr = customField.Calculation.Trim();
    if (string.IsNullOrEmpty(fieldCalcStr)) continue;
    fieldCalcStr = Regex.Replace(fieldCalcStr, @"IIF\(|IIF *\(", "IF(", RegexOptions.IgnoreCase);
    fieldCalcStr = Regex.Replace(fieldCalcStr, " AND ", " AndAlso ", RegexOptions.IgnoreCase);
    fieldCalcStr = Regex.Replace(fieldCalcStr, " OR ", " OrElse ", RegexOptions.IgnoreCase);
    customField.Calculation = fieldCalcStr;
}

最终解决方案 #

通过Regex.Split()将表达式拆分为引号内的字符串片段和非引号内的代码片段，仅对非引号内的部分执行替换操作，彻底解决了引号内内容误替换的问题。

最终代码：

Dictionary<string, string> patternReplacementDict = new Dictionary<string, string>();
patternReplacementDict.Add(@"(?:IIF\s*[(])", "IF(");
patternReplacementDict.Add(@"(?: AND )", " AndAlso ");
patternReplacementDict.Add(@"(?: OR )", " OrElse ");
foreach (CustomFieldInfo customField in Session.ConfigurationManager.GetCustomFields(false))
{
    string calcStr = customField.Calculation.Trim();
    if (string.IsNullOrEmpty(calcStr)) continue;
    string[] calcStrArray = Regex.Split(calcStr, "(\"[^\"]+\")");
    string newCalcStr = string.Empty;
    foreach (string str in calcStrArray)
    {
        if (!str.StartsWith("\""))
        {
            string newStr = str;
            foreach (KeyValuePair<string, string> kvp in patternReplacementDict)
            {
                newStr = Regex.Replace(newStr, kvp.Key, kvp.Value, RegexOptions.IgnoreCase);
            }
            newCalcStr += newStr;
        }
        else
        {
            newCalcStr += str;
        }
    }
    customField.Calculation = newCalcStr;
}

输入输出示例 #

输入 #

IIF([FIELD1] = "This ""quoted text inside string quotes"" and that" AnD [FIELD2] = "This or that", "Value 1",
iiF ([FIELD3] = "This and that" aNd [FIELD4] = "This or that", "Value 2", 
IIF([FIELD4] = "This and that" Or [FIELD5] = "This or that", "Value 3",
Iif   ([FIELD6] = "This and that" oR [FIELD7] = "This or that", "Value 4", 
""))))

输出 #

IF([FIELD1] = "This ""quoted text inside string quotes"" and that" AndAlso [FIELD2] = "This or that", "Value 1",
IF([FIELD3] = "This and that" AndAlso [FIELD4] = "This or that", "Value 2", 
IF([FIELD4] = "This and that" OrElse [FIELD5] = "This or that", "Value 3",
IF([FIELD6] = "This and that" OrElse [FIELD7] = "This or that", "Value 4", 
""))))

内容的提问来源于stack exchange，提问作者lsargent