Expression表達式 實現and、or搜索

用法：

        [HttpPost]
        public ActionResult GetBannerList(int pageIndex, int pageSize, string search)
        {
            Result result = new Result();
            var db = new Credit_CloudEntities();

            Expression<Func<Banner, bool>> expre = x => x.Status == 1;
            if (!string.IsNullOrEmpty(search))
            {
                expre = ExpressionFuncExtender.And(expre, x => x.Title.Contains(search));
            }

            result.Total = db.Banner.Count(expre);

            var list = db.Banner.Where(expre).OrderBy(x => x.Sort).ThenByDescending(x=>x.AddTime)
                .Skip((pageIndex - 1) * pageSize).Take(pageSize)
                .ToList();
            result.Data = list;
            result.ResultCode = (int)ResultCode.Success;
            result.Message = "獲取成功";

            return Json(result);
        }

 

封裝方法：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Text;
using System.Threading.Tasks;

namespace Common
{
    public static class ExpressionFuncExtender
    {
        /// <summary>
        ///     以特定的條件運行組合兩個Expression表達式
        /// </summary>
        /// <typeparam name="T">表達式的主實體類型</typeparam>
        /// <param name="first">第一個Expression表達式</param>
        /// <param name="second">要組合的Expression表達式</param>
        /// <param name="merge">組合條件運算方式</param>
        /// <returns>組合后的表達式</returns>
        public static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second,
            Func<Expression, Expression, Expression> merge)
        {
            var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);
            var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);
            return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);
        }

        /// <summary>
        ///     以 Expression.AndAlso 組合兩個Expression表達式
        /// </summary>
        /// <typeparam name="T">表達式的主實體類型</typeparam>
        /// <param name="first">第一個Expression表達式</param>
        /// <param name="second">要組合的Expression表達式</param>
        /// <returns>組合后的表達式</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>
        ///     以 Expression.OrElse 組合兩個Expression表達式
        /// </summary>
        /// <typeparam name="T">表達式的主實體類型</typeparam>
        /// <param name="first">第一個Expression表達式</param>
        /// <param name="second">要組合的Expression表達式</param>
        /// <returns>組合后的表達式</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.OrElse);
        }

        private class ParameterRebinder : ExpressionVisitor
        {
            private readonly Dictionary<ParameterExpression, ParameterExpression> _map;

            private ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map)
            {
                _map = map ?? new Dictionary<ParameterExpression, ParameterExpression>();
            }

            public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map,
                Expression exp)
            {
                return new ParameterRebinder(map).Visit(exp);
            }

            protected override Expression VisitParameter(ParameterExpression node)
            {
                ParameterExpression replacement;
                if (_map.TryGetValue(node, out replacement))
                    node = replacement;
                return base.VisitParameter(node);
            }
        }
    }
}