c#

Unable to cast object of type ‘System.DBNull’ to type ‘System.DateTime’

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Hi im trying to make a notification system. Basically when i add a new row, a notification will be shown on my notificationspage realtime (i use signalR with razor pages asp.net). But for some reason when i get on that page, i get these errors: Unable to cast object of type ‘System.DBNull’ to type ‘System.DateTime’.
at myWebApp.Controllers.SpeedListener.GetAlarmList() in myWebAppControllersSpeedListener.cs:line 83
at myWebApp.Controllers.SpeedListener.ListenForAlarmNotifications() in myWebAppControllersSpeedListener.cs:line 43

Comparing two table IDs. ASP.NET MVC

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I am currently loading two Orders and Colors tables, I wanted the Colors table to list the items that have the ID equal to Orders. For this, what occurred to me was to assign the IdOrders values ​​to a variable and compare it with my IdOrders (in my table Colors), but it is not possible to assign the database’s balance to my variable

Date Does not accept null value

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I am creating a gridview that allows the user to enter the date (example Date of Completion) of a specific artifact (There are multiple). If I try to enter a null or empty value it crashes. I have looked high and low for an answer to this. The data they enter is updated to a sql server database. I have switched the data back and forth between between date and nvarchar. Also, the value has to bind so it updates the database in the ASP.net.

ASP.Net Core 5.0 Authentication and Authorization

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I am quite new to Blazor and I am trying to understand authentication and authorization. What I did so far is reading the docs Authentication and Authorization in ASP.NET Core Blazor and Rolebased Authorization in Asp.NET Core. I managed to get authentication running, but I am struggeling with authorization. I would like to store every windows user who is visiting my server side app in a database and say User1 is Admin, User2 is Editor etc. and showing users diffrent areas of pages.