ExpressExtensions.cs

using System;
using System.Linq.Expressions;

namespace LH.Common
{
    public static class ExpressExtensions
    {
        public static Expression<Func<T, bool>> Not<T>(this Expression<Func<T, bool>> one)
        {
            var candidateExpr = one.Parameters[0];
            var body = Expression.Not(one.Body);

            return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
        }

        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> one,
            Expression<Func<T, bool>> another)
        {
            var candidateExpr = Expression.Parameter(typeof(T), "candidate");
            var parameterReplacer = new ParameterReplacer(candidateExpr);

            var left = parameterReplacer.Replace(one.Body);
            var right = parameterReplacer.Replace(another.Body);

            var body = Expression.And(left, right);

            return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
        }

        public static Expression<Func<T, bool>> Or<T>(
            this Expression<Func<T, bool>> one, Expression<Func<T, bool>> another)
        {
            var candidateExpr = Expression.Parameter(typeof(T), "candidate");
            var parameterReplacer = new ParameterReplacer(candidateExpr);

            var left = parameterReplacer.Replace(one.Body);
            var right = parameterReplacer.Replace(another.Body);
            var body = Expression.Or(left, right);

            return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
        }
    }
}