/Services/PredicateBuilder.cs

using System;

using System.Linq;

using System.Linq.Expressions;



namespace Contrib.Voting.Services {

    public static class PredicateBuilder {

        public static Expression<Func<T, bool>> True<T>() { return f => true; }

        public static Expression<Func<T, bool>> False<T>() { return f => false; }



        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1,

                                                            Expression<Func<T, bool>> expr2) {

            var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());

            return Expression.Lambda<Func<T, bool>>

                  (Expression.OrElse(expr1.Body, invokedExpr), expr1.Parameters);

        }



        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1,

                                                             Expression<Func<T, bool>> expr2) {

            var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());

            return Expression.Lambda<Func<T, bool>>

                  (Expression.AndAlso(expr1.Body, invokedExpr), expr1.Parameters);

        }

    }

}