Instead of calling String.Contains, call String.IndexOf with a case insensitive StringComparison parameter. Then compare its result with 0, with the Expression.GreaterThanOrEqual expression. You need to provide the extra parameter in your Expression.Call as an Expression.Constant.
You can decide to hardcode one of the case-insensitive StringComparison options, or export it as a parameter of the Filter method, allowing users to decide whether they want case-insensitive search or not.
You can do something like this:
private static Expression<Func<T, bool>> CreateLike<T>(PropertyInfo prop, string value)
{
var parameter = Expression.Parameter(typeof(T), "f");
var propertyAccess = Expression.MakeMemberAccess(parameter, prop);
var indexOf = Expression.Call(propertyAccess, "IndexOf", null, Expression.Constant(value, typeof(string)),Expression.Constant(StringComparison.InvariantCultureIgnoreCase));
var like=Expression.GreaterThanOrEqual(indexOf, Expression.Constant(0));
return Expression.Lambda<Func<T, bool>>(like, parameter);
}
or, with the StringComparison parameter
private static Expression<Func<T, bool>> CreateLike<T>(PropertyInfo prop,
string value,
StringComparison comparison=StringComparison.InvariantCultureIgnoreCase)
{
var parameter = Expression.Parameter(typeof(T), "f");
var propertyAccess = Expression.MakeMemberAccess(parameter, prop);
var indexOf = Expression.Call(propertyAccess, "IndexOf", null,
Expression.Constant(value, typeof(string)),
Expression.Constant(comparison));
var like=Expression.GreaterThanOrEqual(indexOf, Expression.Constant(0));
return Expression.Lambda<Func<T, bool>>(like, parameter);
}
By using a default value for comparison
you avoid creating two overloads for the same job.