如何使用通用列表处理整数或日期时间 [英] how to handle integer or Datetime with Generic List

问题描述

我想创建动态列表我想从列表中过滤项目



这个函数完全适用于字符串，但除了像Int32或DataTime之类的字符串它给出异常

I am tring to create dynamic list i want to filter items from list

this function perfectly work with string but other than string like Int32 or DataTime it gives exception

public static List<T> Filter<T>
         (this List<T> source, string columnName,
          string compValue)
     {
         ParameterExpression parameter = Expression.Parameter(typeof(T), "x");
         Expression property = Expression.Property(parameter, columnName);
         Expression constant = Expression.Constant(compValue);
        if (property.Type == typeof(string)) //this is for testing
         {

             Expression<Func<T, bool>> predicate =

                 GetExpression<T>(columnName, compValue);

             Func<T, bool> compiled = predicate.Compile();
             return source.Where(compiled).ToList();
         }


         return null;
     }

static Expression<Func<T, bool>> GetExpression<T>(string propertyName, string propertyValue)
     {
         var parameterExp = Expression.Parameter(typeof(T), "type");
         var propertyExp = Expression.Property(parameterExp, propertyName);
         MethodInfo method = typeof(string).GetMethod("Contains", new[] { typeof(string) });
         var someValue = Expression.Constant(propertyValue, typeof(string));
         var containsMethodExp = Expression.Call(propertyExp, method, someValue); // on this line i am getting error if i remove if condition of type checking

         return Expression.Lambda<Func<T, bool>>(containsMethodExp, parameterExp);
     }

错误



声明在'System.String'类型上无法使用'System.Int32'类型的实例调用c＃



所以我想要一些可以处理这个问题的函数



实际上我想在mvc中创建数据表Jquery的动态列表

http ：//www.datatables.net/ [ ^ ]



i卡在我的一个列上是整数所以我无法在该列上过滤

所以我在搜索

Error

declared on type 'System.String' cannot be called with instance of type 'System.Int32' c#

so i want some function that can handle this issue

actually i tring to create dynamic list for datatable Jquery in mvc
http://www.datatables.net/[^]

i am stuck on one of my column is integer so i am not able to filter on that column
so i am searching

推荐答案

我现在改变它按预期工作

我想要的字符串

除了字符串我想要等于

I change this now it working as expected
for string i want like
other than string i want equal

static Expression<Func<T, bool>> GetExpression<T>(string propertyName, string propertyValue)
    {
        var parameterExp = Expression.Parameter(typeof(T), "type");
        var propertyExp = Expression.Property(parameterExp, propertyName);
        if (propertyExp.Type == typeof(string))
        {
            MethodInfo method = typeof(string).GetMethod("Contains", new[] { typeof(string) });
            var someValue = Expression.Constant(propertyValue, typeof(string));
            var containsMethodExp = Expression.Call(propertyExp, method, someValue);

            return Expression.Lambda<Func<T, bool>>(containsMethodExp, parameterExp);
        }
        else
        {
            var converter = TypeDescriptor.GetConverter(propertyExp.Type);
           var result = converter.ConvertFrom(propertyValue);
            var someValue = Expression.Constant(result);
            var containsMethodExp = Expression.Equal(propertyExp, someValue);
            return Expression.Lambda<Func<T, bool>>(containsMethodExp, parameterExp);
        }
    }

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