Question

I m building dynamic lambda expression.I got the following operators working for this code “Contains”,”StartsWith”,”EndsWith”.

Source code

var method = typeof(string).GetMethod(opType.ToString(), new[] { typeof(string) }); 
var startsWithDishExpr = Expression.Call(argLeft, method, argRight);

But Like operator didnt work.
I tried this code for “Like” Operator

var likeExpression = Expression.Call(
                    typeof(System.Data.Linq.SqlClient.SqlMethods), "Like", null, argLeft, argRight);

Anyone have answer for this? Please share.

Answer 1

You can’t use System.Data.Linq.SqlClient.SqlMethods, so you have to create a Like method yourself .

---

Example:

void Main()
{
    var argLeft = Expression.Constant("Foobar", typeof(string));
    var argRight = Expression.Constant("F%b%r", typeof(string));

    var likeExpression = Expression.Call(typeof(StringHelper), "Like", null, argLeft, argRight);

    Expression.Lambda(likeExpression).Compile().DynamicInvoke().Dump();
}
public static class StringHelper
{
    public static bool Like(string toSearch, string toFind)
    {
        return new Regex(@"\A" + new Regex(@"\.|\$|\^|\{|\[|\(|\||\)|\*|\+|\?|\\").Replace(toFind, ch => @"\" + ch)
                                                                                  .Replace('_', '.')
                                                                                  .Replace("%", ".*") + @"\z", 
                         RegexOptions.Singleline).IsMatch(toSearch);
    }
}

Output:

True

(example implementation from here)

---

EDIT:

Since you are using Entity Framework, you should use PatIndex instead.

var likeExpression = Expression.GreaterThan(Expression.Call(typeof(SqlFunctions), "PatIndex", null, argLeft, argRight),
                                            Expression.Constant(0, typeof(int?)));