Some expression stuff

gistfile1.txt

namespace ConsoleApplication1
{
    #region

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Linq.Expressions;

    #endregion

    class Program
    {
        static void Main(string[] args)
        {
            var products = new List<Product>
            {
                new Product
                {
                    Category = new Category {Rating = 1},
                    Seller = new Seller {Rating = 50}
                }
            };
            var predicate = PredicateBuilder.True<Product>();
            predicate = predicate.And(p => p.Category, Category.NiceRating);
            predicate = predicate.And(p => p.Seller, Seller.GoodSeller);
            var result = products.AsQueryable().Where(predicate);
        }
    }

    public class Product
    {
        public Category Category { get; set; }
        public Seller Seller { get; set; }
    }

    public class Category : IHaveRating
    {
        public static Expression<Func<IHaveRating, bool>> NiceRating { get; } = c => c.Rating >= 50;

        public int Rating { get; set; }
        public List<Product> Products { get; set; }
    }

    public class Seller : IHaveRating
    {
        public static Expression<Func<IHaveRating, bool>> GoodSeller { get; } = s => s.Rating >= 4;

        public int Rating { get; set; }
        public List<Product> Products { get; set; }
    }

    public interface IHaveRating
    {
        int Rating { get; set; }
    }
    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);
            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);
            return Expression.Lambda<Func<T, bool>>
                (Expression.AndAlso(expr1.Body, invokedExpr), expr1.Parameters);
        }

        public static Expression<Func<TIn, bool>> And<TIn, TInOut>(this Expression<Func<TIn, bool>> target,
            Expression<Func<TIn, TInOut>> input,
            Expression<Func<TInOut, bool>> inOutOut)
        {
            var invoke = Expression.Invoke(input, target.Parameters);
            var invokedExpr = Expression.Invoke(inOutOut, invoke);
            return Expression.Lambda<Func<TIn, bool>>(Expression.AndAlso(target.Body, invokedExpr), target.Parameters);
        }
        public static Expression<Func<TIn, bool>> Or<TIn, TInOut>(this Expression<Func<TIn, bool>> target,
           Expression<Func<TIn, TInOut>> input,
           Expression<Func<TInOut, bool>> inOutOut)
        {

            var invoke = Expression.Invoke(input, target.Parameters);
            var invokedExpr = Expression.Invoke(inOutOut, invoke);
            return Expression.Lambda<Func<TIn, bool>>(Expression.OrElse(target.Body, invokedExpr), target.Parameters);
        }
    }
}