Lambda根据属性名字选择或筛选

 using System;
 using System.Linq.Expressions;

 internal class LambdaHelper
 {
     /// <summary>
     /// 指定属性名字选择指定的属性
     /// </summary>
     /// <typeparam name="TIn">实体类型</typeparam>
     /// <typeparam name="TOut">属性类型</typeparam>
     /// <param name="propertyName">属性名称</param>
     /// <returns></returns>
     public static Func<TIn, TOut> CreatePropertyAccessor<TIn, TOut>(string propertyName)
     {
         var param = Expression.Parameter(typeof(TIn));
         var body = Expression.PropertyOrField(param, propertyName);
         return Expression.Lambda<Func<TIn, TOut>>(body, param).Compile();
     }

     /// <summary>
     /// 指定属性名称和属性值对实体类进行过滤
     /// 用法：var q = db.Where(MakeFilter("ID", 1));
     /// </summary>
     /// <typeparam name="EType"></typeparam>
     /// <param name="propertyName"></param>
     /// <param name="value"></param>
     /// <returns></returns>
     public static Expression<Func<EType, bool>> MakeFilter<EType>(string propertyName, object value)
     {
         var type = typeof(EType);

         var property = type.GetProperty(propertyName);

         var parameter = Expression.Parameter(type, "p");
         var propertyAccess = Expression.MakeMemberAccess(parameter, property);
         var constantValue = Expression.Constant(value);

         var equality = Expression.Equal(propertyAccess, constantValue);

         return Expression.Lambda<Func<EType, bool>>(equality, parameter);
     }

     /*用法:
     var name1 = CreatePropertyAccessor<Obj, string>("Name");
     var name2 = CreatePropertyAccessor<Obj, string>("Name2");
     var name3 = CreatePropertyAccessor<Obj, string>("Name3");

     var o = new Obj() // Obj is a type with those three properties
     {
         Name = "foo",
         Name2 = "bar",
         Name3 = "baz"
     };

     Console.WriteLine(name1(o)); // "foo"
     Console.WriteLine(name2(o)); // "bar"
     Console.WriteLine(name3(o)); // "baz"

     */
 }