Question

Just to avoid confusion I am talking about linq to object and nothing else.
I am working with lots objects in memory and I need to filter them.
we have a screen with lots of options where a user can select many values.

I need to implement something similar to the “Like” operator in sql.
I did found a post about it in this site and uses regex but I have never used it.
I want to know if my string pattern is correct.Should not use “%” “%”?

I have also read that you should use a combination of startWith -endWith and contains,but I have not found any examples that uses all the them combined,just to get a feel how to do it.

I do something like this

string pattern = string.Format(".*{0}.*", criteria.SearchText);
myList= myList.Where(x => x.Message.Like(pattern)).ToList();

public static bool Like(this string s, string pattern, RegexOptions options = RegexOptions.IgnoreCase)
{
    return Regex.IsMatch(s, pattern, options);
}

Any suggestions

Answer 1

If you want to check if a string contains another you can use:

myList = myList.Where(x => x.Message.Contains(criteria.SearchText)).ToList();

or

myList = myList.Where(x => x.Message.IndexOf(criteria.SearchText) != -1).ToList();

(the second variant is good because with IndexOf you can specify the CultureInfo)

If you want to mix a user-defined word in a Regex you should use the Regex.Escape() to escape it, so that if the user writes a*, the searched text is a* instead of any number of a.

string pattern = string.Format(".*{0}.*", Regex.Escape(criteria.SearchText));

But note that as written, it’s equivalent to:

string pattern = string.Format("{0}", Regex.Escape(criteria.SearchText));

because you haven’t put anchors to your regex, so the regex will be searched anywhere in the string.

If you want to anchor the user-defined word, so for example you want to search for words that begin with

string pattern = string.Format("^{0}", Regex.Escape(criteria.SearchText));

or end with

string pattern = string.Format("{0}$", Regex.Escape(criteria.SearchText));