1 using System;  2 using System.Collections.Generic;  3 using System.Linq;  4 using System.Linq.Expressions;  5 using System.Web;  6   7 namespace Test  8 {  9     /// <summary> 10     /// 统一ParameterExpression 11     /// </summary> 12     public class ParameterReplacer : ExpressionVisitor 13     { 14         public ParameterReplacer(ParameterExpression paramExpr) 15         { 16             ParameterExpression = paramExpr; 17         } 18  19         public ParameterExpression ParameterExpression { get; private set; } 20  21         public Expression Replace(Expression expr) 22         { 23             return Visit(expr); 24         } 25  26         protected override Expression VisitParameter(ParameterExpression p) 27         { 28             return ParameterExpression; 29         } 30     } 31     /// <summary> 32     /// Predicate扩展 33     /// </summary> 34     public static class PredicateExtensionses 35     { 36         /// <summary> 37         ///  38         /// </summary> 39         /// <typeparam name="T"></typeparam> 40         /// <returns></returns> 41         public static Expression<Func<T, bool>> True<T>() { return f => true; } 42         /// <summary> 43         ///  44         /// </summary> 45         /// <typeparam name="T"></typeparam> 46         /// <returns></returns> 47         public static Expression<Func<T, bool>> False<T>() { return f => false; } 48         /// <summary> 49         ///  50         /// </summary> 51         /// <typeparam name="T"></typeparam> 52         /// <param name="expLeft"></param> 53         /// <param name="expRight"></param> 54         /// <returns></returns> 55         public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expLeft, Expression<Func<T, bool>> expRight) 56         { 57             var candidateExpr = Expression.Parameter(typeof(T), "candidate"); 58             var parameterReplacer = new ParameterReplacer(candidateExpr); 59  60             var left = parameterReplacer.Replace(expLeft.Body); 61             var right = parameterReplacer.Replace(expRight.Body); 62             var body = Expression.And(left, right); 63  64             return Expression.Lambda<Func<T, bool>>(body, candidateExpr); 65         } 66         /// <summary> 67         ///  68         /// </summary> 69         /// <typeparam name="T"></typeparam> 70         /// <param name="expLeft"></param> 71         /// <param name="expRight"></param> 72         /// <returns></returns> 73         public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expLeft, Expression<Func<T, bool>> expRight) 74         { 75             var candidateExpr = Expression.Parameter(typeof(T), "candidate"); 76             var parameterReplacer = new ParameterReplacer(candidateExpr); 77  78             var left = parameterReplacer.Replace(expLeft.Body); 79             var right = parameterReplacer.Replace(expRight.Body); 80             var body = Expression.Or(left, right); 81  82             return Expression.Lambda<Func<T, bool>>(body, candidateExpr); 83         } 84     } 85     /// <summary> 86     /// Queryable扩展 87     /// </summary> 88     public static class QueryableExtensions 89     { 90         /// <summary> 91         ///  92         /// </summary> 93         /// <typeparam name="T"></typeparam> 94         /// <param name="queryable"></param> 95         /// <param name="propertyName"></param> 96         /// <returns></returns> 97         public static IQueryable<T> OrderBy<T>(this IQueryable<T> queryable, string propertyName) 98         { 99             return OrderBy(queryable, propertyName, false);100         }101         /// <summary>102         /// OrderBy103         /// </summary>104         /// <typeparam name="T">实体</typeparam>105         /// <param name="queryable">条件</param>106         /// <param name="propertyName">属性名称</param>107         /// <param name="desc">是否降序</param>108         /// <returns></returns>109         public static IQueryable<T> OrderBy<T>(this IQueryable<T> queryable, string propertyName, bool desc)110         {111             var param = Expression.Parameter(typeof(T));112             var body = Expression.Property(param, propertyName);113             dynamic keySelector = Expression.Lambda(body, param);114             return desc ? Queryable.OrderByDescending(queryable, keySelector) : Queryable.OrderBy(queryable, keySelector);115         }116     }117 }