Like operator or using wildcards in LINQ to Entities

Question

I\'m using LINQ 2 Entities. Following is the problem:

string str = \'%test%.doc%\' 
.Contains(str) // converts this into LIKE \'%~%test~%.doc~%%\'

Answer 1

You can try use this article, where author describes how to build a LIKE statement with wildcard characters in LINQ to Entities.

EDIT: Since the original link is now dead, here is the original extension class (as per Jon Koeter in the comments) and usage example.

Extension:

public static class LinqHelper
{
    //Support IQueryable (Linq to Entities)
    public static IQueryable WhereLike(this IQueryable source, Expression> valueSelector, string value, char wildcard)
    {
        return source.Where(BuildLikeExpression(valueSelector, value, wildcard));
    }

    //Support IEnumerable (Linq to objects)
    public static IEnumerable WhereLike(this IEnumerable sequence, Func expression, string value, char wildcard)
    {
        var regEx = WildcardToRegex(value, wildcard);

        //Prevent multiple enumeration:
        var arraySequence = sequence as TSource[] ?? sequence.ToArray();

        try
        {
            return arraySequence.Where(item => Regex.IsMatch(expression(item), regEx));
        }
        catch (ArgumentNullException)
        {
            return arraySequence;
        }
    }

    //Used for the IEnumerable support
    private static string WildcardToRegex(string value, char wildcard)
    {
        return "(?i:^" + Regex.Escape(value).Replace("\\" + wildcard, "." + wildcard) + "$)";
    }

    //Used for the IQueryable support
    private static Expression> BuildLikeExpression(Expression> valueSelector, string value, char wildcard)
    {
        if (valueSelector == null) throw new ArgumentNullException("valueSelector");

        var method = GetLikeMethod(value, wildcard);

        value = value.Trim(wildcard);
        var body = Expression.Call(valueSelector.Body, method, Expression.Constant(value));

        var parameter = valueSelector.Parameters.Single();
        return Expression.Lambda>(body, parameter);
    }

    private static MethodInfo GetLikeMethod(string value, char wildcard)
    {
        var methodName = "Equals";

        var textLength = value.Length;
        value = value.TrimEnd(wildcard);
        if (textLength > value.Length)
        {
            methodName = "StartsWith";
            textLength = value.Length;
        }

        value = value.TrimStart(wildcard);
        if (textLength > value.Length)
        {
            methodName = (methodName == "StartsWith") ? "Contains" : "EndsWith";
        }

        var stringType = typeof(string);
        return stringType.GetMethod(methodName, new[] { stringType });
    }
}

Usage Example:

string strEmailToFind = "%@yahoo.com"

IQueryable myUsers = entities.Users.WhereLike(u => u.EmailAddress, strEmailToFind, '%');

or, if you expect your users to be more accustomed to Windows Explorer-styled wildcards:

string strEmailToFind = "*@yahoo.com"

IQueryable myUsers = entities.Users.WhereLike(u => u.EmailAddress, strEmailToFind, '*');