juipnet/Infrastructure/Hncore.Infrastructure/EntitiesExtension/ExpressionBuilder.cs

using System;
using System.Linq;
using System.Linq.Expressions;

namespace Hncore.Infrastructure.EntitiesExtension
{
    /// <summary>
    /// Extension methods for add And and Or with parameters rebinder
    /// </summary>
    public static class ExpressionBuilder
    {
        /// <summary>
        /// Compose two expression and merge all in a new expression
        /// </summary>
        /// <typeparam name="T">Type of params in expression</typeparam>
        /// <param name="first">Expression instance</param>
        /// <param name="second">Expression to merge</param>
        /// <param name="merge">Function to merge</param>
        /// <returns>New merged expressions</returns>
        public static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge)
        {
            // build parameter map (from parameters of second to parameters of first)
            var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);

            // replace parameters in the second lambda expression with parameters from the first
            var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);
            // apply composition of lambda expression bodies to parameters from the first expression 
            return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);
        }
        /// <summary>
        /// And operator
        /// </summary>
        /// <typeparam name="T">Type of params in expression</typeparam>
        /// <param name="first">Right Expression in AND operation</param>
        /// <param name="second">Left Expression in And operation</param>
        /// <returns>New AND expression</returns>
        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
        {
            return first.Compose(second, Expression.AndAlso);
        }
        /// <summary>
        /// Or operator
        /// </summary>
        /// <typeparam name="T">Type of param in expression</typeparam>
        /// <param name="first">Right expression in OR operation</param>
        /// <param name="second">Left expression in OR operation</param>
        /// <returns>New Or expressions</returns>
        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
        {
            return first.Compose(second, Expression.Or);
        }
    }
}