Question

我正在使用列排序。这是我的代码返回IQueryable结果。在这里，我向App_Code端添加了一个Helper类，并为列排序创建了一个静态IQueryable方法。

public static class Helper
{
    public static IQueryable<T> FilterForColumn<T>(this IQueryable<T> queryable, string colName, string searchText)
    {
        if (colName != null && searchText != null)
        {
            var parameter = Expression.Parameter(typeof(T), "m");
            var propertyExpression = Expression.Property(parameter, colName);
            System.Linq.Expressions.ConstantExpression searchExpression = null;
            System.Reflection.MethodInfo containsMethod = null;
            switch (colName)
            {
                case "Title":
                case "Publisher":
                case "ToUser":
                case "CategoryName":
                case "StatusName":
                case "GroupName":
                case "FileSize":
                    searchExpression = Expression.Constant(searchText);
                    containsMethod = typeof(string).GetMethod("Contains", new[] { typeof(string) });
                    break;
                case "PublishDate":
                    DateTime dt = DateTime.ParseExact(searchText, "dd/MM/yyyy", null);
                    searchExpression = Expression.Constant(dt.Date.ToString("MM/dd/yyyy"));
                    containsMethod = typeof(DateTime).GetMethod("Equals", new[] { typeof(DateTime) });
                    break;
            }
            var body = Expression.Call(propertyExpression, containsMethod, searchExpression);
            var predicate = Expression.Lambda<Func<T, bool>>(body, new[] { parameter });
            return queryable.Where(predicate);
        }
        else
        {
            return queryable;
        }
    }
}

但是PublishDate部分出现了错误：

Server Error in '/EasyWeb' Application.
Method 'Boolean Equals(System.DateTime)' is not defined for type 'System.Nullable`1[System.DateTime]'
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.ArgumentException: Method 'Boolean Equals(System.DateTime)' is not defined for type 'System.Nullable`1[System.DateTime]'

Source Error:


Line 40:                     break;
Line 41:             }
Line 42:             var body = Expression.Call(propertyExpression, containsMethod, searchExpression);
Line 43:             var predicate = Expression.Lambda<Func<T, bool>>(body, new[] { parameter });
Line 44:             return queryable.Where(predicate);


Source File: f:\EasyWeb\App_Code\Helper.cs    Line: 42

Stack Trace:


[ArgumentException: Method 'Boolean Equals(System.DateTime)' is not defined for type 'System.Nullable`1[System.DateTime]']
   System.Linq.Expressions.Expression.ValidateCallInstanceType(Type instanceType, MethodInfo method) +763804
   System.Linq.Expressions.Expression.ValidateCallArgs(Expression instance, MethodInfo method, ReadOnlyCollection`1& arguments) +71
   System.Linq.Expressions.Expression.Call(Expression instance, MethodInfo method, IEnumerable`1 arguments) +46
   System.Linq.Expressions.Expression.Call(Expression instance, MethodInfo method, Expression[] arguments) +31
   Helper.FilterForColumn(IQueryable`1 queryable, String colName, String searchText) in f:\EasyWeb\App_Code\Helper.cs:42
   Admin_Post_History.FillGrid(String CommandName, String ColumnName, String SearchText) in f:\EasyWeb\Admin\Post_History.aspx.cs:63
   Admin_Post_History.btnsearch_Click(Object sender, EventArgs e) in f:\EasyWeb\Admin\Post_History.aspx.cs:2414
   System.Web.UI.WebControls.Button.OnClick(EventArgs e) +111
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +110
   System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +36
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1565

请帮助我，我在这里出错了。

Answer 1

您在colName中传递的属性看起来像DateTime?而不是DateTime，这意味着您无法将其作为参数传递给DateTime.Equals(DateTime)。

方法'Boolean Equals（System.DateTime）'未定义类型'System.Nullable`1 [System.DateTime]'

1 个答案: