如何在Entity Framework中将字段设置为DBNull [英] How do I set a field to DBNull in Entity Framework

问题描述

如何在Entity Framework中将字段设置为DBNull？这些字段是强类型的，因此您不能将其设置为等于DBNull.Value，我没有找到任何方法将字段设置为DBNull。看来这是一件必要的事情，但经过大量的Google研究，我没有发现任何事情。

How do you set a field to DBNull in Entity Framework? The fields are strongly typed so you cannot set it equal to DBNull.Value and I did not find any method to set a field to DBNull. It seems like this is a necessary thing to do, but after much Google research I found nothing about it.

我试图使用vb在Entity Framework中设置一个datetime字段。净。这需要我写

I am trying to set a datetime field in Entity Framework using vb.net. This requires me to write

 myEntity.mydate = Nothing

这不会将该字段设置为空，而是将其设置为SQL Server中不是有效日期值的默认日期值。

This does not set the field to null but instead sets it to the default date value which is not a valid date value in SQL Server.

推荐答案

如果列在数据库中为空，则结果类也将具有可空属性。

If a column is nullable in the database the result class will have a nullable property too.

例如，如果订单表具有可空的 Datetime 列，名为 CreatedDate ，那么结果订单类将看起来像这样：

For example if a Order table has a nullable Datetime column called CreatedDate, then the resulting Order class will looks something like this:

public partial class Order: EntityObject
{
  ...
  private DateTime? _createdDate;
  ...
}

如果_ createDate 当您调用 ObjectContext.SaveChanges（） a System.DBNull 将无效自动发送到数据库作为插入或更新命令的一部分。

If the _createdDate has no value when you call ObjectContext.SaveChanges() a System.DBNull will automatically be sent to the database as part of insert or update command.

希望这有助于
Alex

Hope this helps Alex

这篇关于如何在Entity Framework中将字段设置为DBNull的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！