Wildcard Search Helper Entity Framework

EFWildcardSearch.md

Wildcard Search Helper Entity Framework

You can build a LIKE statement with wildcard characters in LINQ to Entities with this Helper.

LinqHelper.cs

public static class LinqHelper
{
    public static IQueryable<TSource> WhereLike<TSource>(this IQueryable<TSource> source, Expression<Func<TSource, string>> valueSelector, string value, char wildcard)
    {
        return source.Where(BuildLikeExpression(valueSelector, value, wildcard));
    }

    public static IEnumerable<TSource> WhereLike<TSource>(this IEnumerable<TSource> sequence, Func<TSource, string> 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;
        }
    }

    private static string WildcardToRegex(string value, char wildcard)
    {
        return "(?i:^" + Regex.Escape(value).Replace(@"\" + wildcard, "." + wildcard) + "$)";
    }

    private static Expression<Func<TElement, bool>> BuildLikeExpression<TElement>(Expression<Func<TElement, string>> valueSelector, string value, char wildcard)
    {
        if (valueSelector == null) throw new ArgumentNullException(nameof(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<Func<TElement, bool>>(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.cs

public class CitiesController : Controller
{
    private readonly ApplicationDbContext _db = new ApplicationDbContext();

    [HttpGet]
    public ActionResult Index()
    {
        return View(_db.Cities.ToList());
    }

    [HttpPost]
    public ActionResult Index(string searchTerm)
    {
        var cities = _db.Cities.AsQueryable();

        if (!string.IsNullOrWhiteSpace(searchTerm))
        {
	    searchTerm = $"%{searchTerm}%";
			
	    // OR
            //searchTerm = $"%{searchTerm}";
            //searchTerm = $"{searchTerm}%";
			
            cities = cities.WhereLike(x => x.Name, searchTerm, '%');
        }

        return View("Index", cities.ToList());
    }
}