Filtering Comma Separated Data - linq

Question

My site has a bunch of widgets and i'm trying to filter them based on the url which is passed in. Say a Widget has the following structure:
public class Widget {
public int Id { get; set; }
public string Name { get; set; }
public string Urls { get; set; }
}
Where Urls is a comma separated list for the urls where the widget should be displayed, e.g.:
/, /Blog/, /Blog/123, /News/*
The asterisk after News indicates the Widget will be selected whenever the passed in url starts with /News/.
How could i modify the following method to filter the widgets based on my conditions above?
public IList<Widget> GetWidgets(string url) {
return _session
.Where(w => w.Urls.Contains(url))
.ToList();
}
Ideally i'd like to use a linq query and it must only hit the database once. I'd appreciate the help. Thanks

Answer 1

I managed to solve this by adding my own wild card match generator. See http://sentinel101.wordpress.com/2010/12/30/extend-nhibernate-linq-for-regex-matching/ for example of how to register the generator. Here's the generator incase anyone is interested:
public class WildCardMatchGenerator : BaseHqlGeneratorForMethod {
public WildCardMatchGenerator() {
var methodDefinition = ReflectionHelper.GetMethodDefinition(() => WildCardMatchExtensions.WildCardMatch(null, null, ','));
SupportedMethods = new[] { methodDefinition };
}
public override HqlTreeNode BuildHql(MethodInfo method, Expression targetObject, ReadOnlyCollection<Expression> arguments, HqlTreeBuilder treeBuilder, IHqlExpressionVisitor visitor) {
return treeBuilder.Equality(treeBuilder.MethodCall("[dbo].[WildCardMatch]", new[] {
visitor.Visit(arguments[0]).AsExpression(),
visitor.Visit(arguments[1]).AsExpression(),
visitor.Visit(arguments[2]).AsExpression()
}), treeBuilder.Constant(1));
}
}
And here is the WildCardMatch UDF:
CREATE FUNCTION [dbo].[WildCardMatch] (
#Pattern NVARCHAR(MAX),
#Input NVARCHAR(MAX),
#Separator NVARCHAR(5)
)
RETURNS BIT
AS
BEGIN
SET #Pattern = REPLACE(#Pattern, '*', '%')
DECLARE #RtnValue BIT
SELECT #RtnValue = CASE WHEN COUNT(*) > 0 THEN 1 ELSE 0 END FROM [dbo].[Split](#Pattern, #Separator) WHERE #Input LIKE [Data]
RETURN #RtnValue
END
And the Split function it calls (from http://blogs.microsoft.co.il/blogs/itai/archive/2009/02/01/t-sql-split-function.aspx):
CREATE FUNCTION [dbo].[Split]
(
#RowData NVARCHAR(MAX),
#Separator NVARCHAR(MAX)
)
RETURNS #RtnValue TABLE
(
[Id] INT IDENTITY(1,1),
[Data] NVARCHAR(MAX)
)
AS
BEGIN
DECLARE #Iterator INT
SET #Iterator = 1
DECLARE #FoundIndex INT
SET #FoundIndex = CHARINDEX(#Separator, #RowData)
WHILE (#FoundIndex > 0)
BEGIN
INSERT INTO #RtnValue ([Data])
SELECT Data = LTRIM(RTRIM(SUBSTRING(#RowData, 1, #FoundIndex - 1)))
SET #RowData = SUBSTRING(#RowData, #FoundIndex + DATALENGTH(#Separator) / 2, LEN(#RowData))
SET #Iterator = #Iterator + 1
SET #FoundIndex = CHARINDEX(#Separator, #RowData)
END
INSERT INTO #RtnValue ([Data])
SELECT Data = LTRIM(RTRIM(#RowData))
RETURN
END
Lastly you'll need the C# implementation of the above UDF:
public static class WildCardMatchExtensions {
public static bool WildCardMatch(this string pattern, string input, char separator = ',') {
foreach (var str in pattern.Split(new char[] { separator }, StringSplitOptions.RemoveEmptyEntries)) {
if (Regex.IsMatch(input, Regex.Escape(str.Trim()).Replace("\\*", ".*")))
return true;
}
return false;
}
}
Hope this helps.

Answer 2

I don't think SQL server allows you to use IN for comma delimited field values. You need LIKE (SQL example below):
Urls LIKE '%_your_url_%'
Linq, Expressions, NHibernate and Like comparison may help you with translation LIKE to Linq to NHibernate