How to implement LessThan, etc., when building expressions on strings

Question

I have a package in which I\'m building expression trees, to use with EntityFramework, via PredicateBuilder:

public Expression> con         


        

Answer 1

This works:

Expression comparison = null;

if (value.Type == typeof (string))
{
    if (operation == ExpressionType.GreaterThanOrEqual ||
        operation == ExpressionType.GreaterThan ||
        operation == ExpressionType.LessThanOrEqual ||
        operation == ExpressionType.LessThan)
    {
        var method = value.Type.GetMethod("CompareTo", new[] {typeof (string)});
        var zero = Expression.Constant(0);

        var result = Expression.Call(member, method, converted);

        comparison = Expression.MakeBinary(operation, result, zero);
    }
}

if (comparison == null)
    comparison = Expression.MakeBinary(operation, member, converted);

var lambda = Expression.Lambda<Func<T, bool>>(comparison, parameter);