LINQ动态查询类--[DynamicLinqExpressions]

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

 namespace Test
 {
     /// <summary>
     /// 一個老外寫的擴充Expression方法的靜態類別,可以解決上面冗長的程式碼
     /// </summary>
     public static class DynamicLinqExpressions//注意static靜態型別
     {
         public static Expression<Func<T, bool>> True<T>() { return f => true; }
         public static Expression<Func<T, bool>> False<T>() { return f => false; }

         //注意this
         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.Cast<Expression>());
             return Expression.Lambda<Func<T, bool>>
                   (Expression.Or(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.Cast<Expression>());
             return Expression.Lambda<Func<T, bool>>
                   (Expression.And(expr1.Body, invokedExpr), expr1.Parameters);
         }
     }
 }

使用示例：

 SchoolContainer school = new SchoolContainer();
             var eps = DynamicLinqExpressions.True<Teacher>();
             eps.And(T=>T.Name.Contains(""));
             var ss = school.Teacher.Where(T => T.Name.Contains("PM")).Where(eps);
             foreach (var item in ss)
             {
                 Console.WriteLine(item.Name);
             }