c# Lambda扩展

扩展类

  public static class LinqExtensions
     {
         /// <summary>
         /// 创建lambda表达式：p=>true
         /// </summary>
         /// <typeparam name="T">对象名称（类名）</typeparam>
         /// <returns></returns>
         public static Expression<Func<T, bool>> True<T>()
         {
             return p => true;
         }

         /// <summary>
         /// 创建lambda表达式：p=>false
         /// </summary>
         /// <typeparam name="T">对象名称（类名）</typeparam>
         /// <returns></returns>
         public static Expression<Func<T, bool>> False<T>()
         {
             return p => false;
         }

         /// <summary>
         /// 创建lambda表达式：p=>p.propertyName
         /// </summary>
         /// <typeparam name="T">对象名称（类名）</typeparam>
         /// <typeparam name="TKey">参数类型</typeparam>
         /// <param name="propertyName">字段名称（数据库中字段名称）</param>
         /// <returns></returns>
         public static Expression<Func<T, TKey>> GetOrderExpression<T, TKey>(string propertyName)
         {
             ParameterExpression parameter = Expression.Parameter(typeof(T), "p");
             return Expression.Lambda<Func<T, TKey>>(Expression.Property(parameter, propertyName), parameter);
         }

         /// <summary>
         /// 创建lambda表达式：p=>p.propertyName == propertyValue
         /// </summary>
         /// <typeparam name="T">对象名称（类名）</typeparam>
         /// <param name="propertyName">字段名称（数据库中字段名称）</param>
         /// <param name="propertyValue">数据值</param>
         /// <returns></returns>
         public static Expression<Func<T, bool>> CreateEqual<T>(string propertyName, object propertyValue, Type typeValue)
         {
             ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
             MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
             ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//创建常数
             return Expression.Lambda<Func<T, bool>>(Expression.Equal(member, constant), parameter);
         }

         /// <summary>
         /// 创建lambda表达式：p=>p.propertyName != propertyValue
         /// </summary>
         /// <typeparam name="T">对象名称（类名）</typeparam>
         /// <param name="propertyName">字段名称（数据库中字段名称）</param>
         /// <param name="propertyValue">数据值</param>
         /// <returns></returns>
         public static Expression<Func<T, bool>> CreateNotEqual<T>(string propertyName, object propertyValue, Type typeValue)
         {
             ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
             MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
             ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//创建常数
             return Expression.Lambda<Func<T, bool>>(Expression.NotEqual(member, constant), parameter);
         }

         /// <summary>
         /// 创建lambda表达式：p=>p.propertyName > propertyValue
         /// </summary>
         /// <typeparam name="T">对象名称（类名）</typeparam>
         /// <param name="propertyName">字段名称（数据库中字段名称）</param>
         /// <param name="propertyValue">数据值</param>
         /// <returns></returns>
         public static Expression<Func<T, bool>> CreateGreaterThan<T>(string propertyName, object propertyValue, Type typeValue)
         {
             ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
             MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
             ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//创建常数
             return Expression.Lambda<Func<T, bool>>(Expression.GreaterThan(member, constant), parameter);
         }

         /// <summary>
         /// 创建lambda表达式：p=>p.propertyName小于propertyValue
         /// </summary>
         /// <typeparam name="T">对象名称（类名）</typeparam>
         /// <param name="propertyName">字段名称（数据库中字段名称）</param>
         /// <param name="propertyValue">数据值</param>
         /// <returns></returns>
         public static Expression<Func<T, bool>> CreateLessThan<T>(string propertyName, object propertyValue, Type typeValue)
         {
             ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
             MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
             ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//创建常数
             return Expression.Lambda<Func<T, bool>>(Expression.LessThan(member, constant), parameter);
         }

         /// <summary>
         /// 创建lambda表达式：p=>p.propertyName >= propertyValue
         /// </summary>
         /// <typeparam name="T">对象名称（类名）</typeparam>
         /// <param name="propertyName">字段名称（数据库中字段名称）</param>
         /// <param name="propertyValue">数据值</param>
         /// <returns></returns>
         public static Expression<Func<T, bool>> CreateGreaterThanOrEqual<T>(string propertyName, object propertyValue, Type typeValue)
         {
             ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
             MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
             ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//创建常数
             return Expression.Lambda<Func<T, bool>>(Expression.GreaterThanOrEqual(member, constant), parameter);
         }

         /// <summary>
         /// 创建lambda表达式：p=> p.propertyName 小于= propertyValue
         /// </summary>
         /// <typeparam name="T">对象名称（类名）</typeparam>
         /// <param name="propertyName">字段名称（数据库中字段名称）</param>
         /// <param name="propertyValue">数据值</param>
         /// <returns></returns>
         public static Expression<Func<T, bool>> CreateLessThanOrEqual<T>(string propertyName, object propertyValue, Type typeValue)
         {
             ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
             MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
             ConstantExpression constant = Expression.Constant(propertyValue, typeValue);//创建常数
             return Expression.Lambda<Func<T, bool>>(Expression.LessThanOrEqual(member, constant), parameter);
         }

         /// <summary>
         /// 创建lambda表达式：p=>p.propertyName.Contains(propertyValue)
         /// </summary>
         /// <typeparam name="T">对象名称（类名）</typeparam>
         /// <param name="propertyName">字段名称（数据库中字段名称）</param>
         /// <param name="propertyValue">数据值</param>
         /// <returns></returns>
         public static Expression<Func<T, bool>> GetContains<T>(string propertyName, string propertyValue)
         {
             ParameterExpression parameter = Expression.Parameter(typeof(T), "p");
             MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
             MethodInfo method = typeof(string).GetMethod("Contains", new[] { typeof(string) });
             ConstantExpression constant = Expression.Constant(propertyValue, typeof(string));
             return Expression.Lambda<Func<T, bool>>(Expression.Call(member, method, constant), parameter);
         }

         /// <summary>
         /// 创建lambda表达式：!(p=>p.propertyName.Contains(propertyValue))
         /// </summary>
         /// <typeparam name="T">对象名称（类名）</typeparam>
         /// <param name="propertyName">字段名称（数据库中字段名称）</param>
         /// <param name="propertyValue">数据值</param>
         /// <returns></returns>
         public static Expression<Func<T, bool>> GetNotContains<T>(string propertyName, string propertyValue)
         {
             ParameterExpression parameter = Expression.Parameter(typeof(T), "p");
             MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
             MethodInfo method = typeof(string).GetMethod("Contains", new[] { typeof(string) });
             ConstantExpression constant = Expression.Constant(propertyValue, typeof(string));
             return Expression.Lambda<Func<T, bool>>(Expression.Not(Expression.Call(member, method, constant)), parameter);
         }

         /// <summary>
         /// 功能描述:拼接Or
         /// 作　　者:beck.huang
         /// 创建日期:2018-11-30 15:35:10
         /// 任务编号:好餐谋后台管理系统
         /// </summary>
         /// <param name="expression1">expression1</param>
         /// <param name="expression2">expression2</param>
         /// <returns>返回值</returns>
         public static Expression<Func<T, bool>> Or<T>(Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2)
         {
             return Compose(expression1, expression2, Expression.OrElse);
         }

         /// <summary>
         /// 功能描述:拼接And
         /// 作　　者:beck.huang
         /// 创建日期:2018-11-30 15:35:18
         /// 任务编号:好餐谋后台管理系统
         /// </summary>
         /// <param name="expression1">expression1</param>
         /// <param name="expression2">expression2</param>
         /// <returns>返回值</returns>
         public static Expression<Func<T, bool>> And<T>(Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2)
         {
             return Compose(expression1, expression2, Expression.AndAlso);
         }

         /// <summary>
         /// 功能描述:合并2个表达式
         /// 作　　者:beck.huang
         /// 创建日期:2018-11-30 15:35:26
         /// 任务编号:好餐谋后台管理系统
         /// </summary>
         /// <param name="first">first</param>
         /// <param name="second">second</param>
         /// <param name="merge">merge</param>
         /// <returns>返回值</returns>
         public static Expression<T> Compose<T>(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);
         }
         private class ParameterRebinder : ExpressionVisitor
         {
             readonly Dictionary<ParameterExpression, ParameterExpression> map;
             /// <summary>
             /// Initializes a new instance of the <see cref="ParameterRebinder"/> class.
             /// </summary>
             /// <param name="map">The map.</param>
             ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map)
             {
                 this.map = map ?? new Dictionary<ParameterExpression, ParameterExpression>();
             }
             /// <summary>
             /// Replaces the parameters.
             /// </summary>
             /// <param name="map">The map.</param>
             /// <param name="exp">The exp.</param>
             /// <returns>Expression</returns>
             public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map, Expression exp)
             {
                 return new ParameterRebinder(map).Visit(exp);
             }
             protected override Expression VisitParameter(ParameterExpression p)
             {
                 ParameterExpression replacement;

                 if (map.TryGetValue(p, out replacement))
                 {
                     p = replacement;
                 }
                 return base.VisitParameter(p);
             }
         }
     }