jqgrid with asp.net webmethod and json working with sorting, paging, searching and LINQ -- but needs dynamic operators

Consider this extension method, that converts a string into a MemberExpression:

public static class StringExtensions{    public static MemberExpression ToMemberExpression(this string source, ParameterExpression p)    {        if (p == null)            throw new ArgumentNullException("p");        string[] properties = source.Split('.');        Expression expression = p;        Type type = p.Type;        foreach (var prop in properties)        {            var property = type.GetProperty(prop);            if (property == null)                throw new ArgumentException("Invalid expression", "source");            expression = Expression.MakeMemberAccess(expression, property);            type = property.PropertyType;        }        return (MemberExpression)expression;    }}

The method below converts the strings that you have into an Lambda Expression, that you can use to filter a Linq query. It is a generic method, with T as the domain entity.

    public virtual Expression<Func<T, bool>> CreateExpression<T>(string searchField, string searchString, string searchOper)    {        Expression exp = null;        var p = Expression.Parameter(typeof(T), "p");        try        {            Expression propertyAccess = searchField.ToExpression(p);            switch (searchOper)            {                case "bw":                    exp = Expression.Call(propertyAccess, typeof(string).GetMethod("StartsWith", new Type[] { typeof(string) }), Expression.Constant(searchString));                    break;                case "cn":                    exp = Expression.Call(propertyAccess, typeof(string).GetMethod("Contains", new Type[] { typeof(string) }), Expression.Constant(searchString));                    break;                case "ew":                    exp = Expression.Call(propertyAccess, typeof(string).GetMethod("EndsWith", new Type[] { typeof(string) }), Expression.Constant(searchString));                    break;                case "gt":                    exp = Expression.GreaterThan(propertyAccess, Expression.Constant(searchString, propertyAccess.Type));                    break;                case "ge":                    exp = Expression.GreaterThanOrEqual(propertyAccess, Expression.Constant(searchString, propertyAccess.Type));                    break;                case "lt":                    exp = Expression.LessThan(propertyAccess, Expression.Constant(searchString, propertyAccess.Type));                    break;                case "le":                    exp = Expression.LessThanOrEqual(propertyAccess, Expression.Constant(searchString, propertyAccess.Type));                    break;                case "eq":                    exp = Expression.Equal(propertyAccess, Expression.Constant(searchString.ToType(propertyAccess.Type), propertyAccess.Type));                    break;                case "ne":                    exp = Expression.NotEqual(propertyAccess, Expression.Constant(searchString, propertyAccess.Type));                    break;                default:                    return null;            }            return (Expression<Func<T, bool>>)Expression.Lambda(exp, p);        }        catch        {            return null;        }    }

So, you can use it like this:

db.TBL_USERs.Where(CreateExpression<TBL_USER>("LAST_NAME", "Costa", "eq"));

Give this article a peep. It is focused on using jqgrid in MVC but you can extract the relevant information.