/// <summary>
/// This method parses a friendly Derived Columns expression entered by the user into a Lineage-ID based
/// expression which is required by SSIS, using a regular-expression based parser.
/// Additionally, it will set the Input Column Usage for any columns found in the expression.
/// </summary>
/// <param name="expression">Expression to be parsed.</param>
/// <param name="transformation">Transformation to use for evaluating the lineage IDs</param>
/// <param name="vi">Transformation Virtual Input used to search for input columns.</param>
/// <param name="inputColumnUsageType">DTSUsageType for columns mapped in this expression.</param>
/// <returns>Expression struct with the pre-processed and post-processed expression.</returns>
public static Expression ExpressionCleanerAndInputMapBuilder(string expression, Transformation transformation, IDTSVirtualInput100 vi, DTSUsageType inputColumnUsageType)
{
Expression exp = new Expression();
exp.OriginalExpression = expression;
exp.ProcessedExpression = expression;
exp.FriendlyExpression = expression;
exp.ContainsId = false;
foreach (IDTSVirtualInputColumn100 vcol in vi.VirtualInputColumnCollection)
{
string regexString = String.Format(CultureInfo.CurrentCulture, "(\"(?:[^\"]|(?<=\\\\)\")*\")|(?<vCol>(?<!@\\[?|:)\\[?\\b{0}\\b\\]?)", Regex.Escape(vcol.Name));
var regex = new Regex(regexString, RegexOptions.IgnoreCase | RegexOptions.CultureInvariant);
int groupNumber = regex.GroupNumberFromName("vCol");
var processedEme = new ExpressionMatchEvaluatorStruct(groupNumber, "#" + vcol.LineageID, transformation, vi, inputColumnUsageType, vcol);
var friendlyEme = new ExpressionMatchEvaluatorStruct(groupNumber, vcol.Name, null, null, DTSUsageType.UT_IGNORED, null);
exp.ProcessedExpression = regex.Replace(exp.ProcessedExpression, new MatchEvaluator(processedEme.EvaluateMatch));
exp.FriendlyExpression = regex.Replace(exp.FriendlyExpression, new MatchEvaluator(friendlyEme.EvaluateMatch));
}
if (exp.ProcessedExpression != exp.OriginalExpression)
{
exp.ContainsId = true;
}
return exp;
}
public ExpressionMatchEvaluatorStruct(
int groupNum,
string text,
Transformation trans,
IDTSVirtualInput100 vi,
DTSUsageType inputColumnUsageType,
IDTSVirtualInputColumn100 vcol)
{
this.groupNum = groupNum;
this.text = text;
this.trans = trans;
this.vi = vi;
this.inputColumnUsageType = inputColumnUsageType;
this.vcol = vcol;
}