如何处理SQL Server NULL值

I'm trying to get values from my database, it works when all columns have values. When a value is NULL, it returns an error.

我正在尝试从我的数据库中获取值,它在所有列都有值时起作用。当值为NULL时,它将返回错误。

I've managed to find a way to handle with the strings but if there's an integer I don't know how to handle it. I've tried to find a solution but none has worked for me so far! Here's the code, any help would be highly appreciated.

我已经设法找到一种方法来处理字符串,但如果有一个整数我不知道如何处理它。我试图找到一个解决方案但到目前为止没有一个对我有用!这是代码,任何帮助将受到高度赞赏。

Thanks!

while (dr.Read())
{
    coments comentsar = new coments
            {
                Id = (int)dr["Id"],
                Name = (string)dr["Name"],
                Likes = (int)dr["Likes"],
          //    Signature = dr["Signature"].ToString(),
                Datetime = (DateTime)dr["Datetime"]
            };

    comen.Add(comentsar);

    return comen;
}

2 个解决方案

#1

You can check for null value and if the value is not null assign the variable using ternary operator:

您可以检查空值,如果值不为null,则使用三元运算符分配变量:

Signature  = dr["Signature"] != DBNull.Value ? (string)dr["Signature"] : "No value",
Likes = dr["Likes"] != DBNull.Value ? Convert.ToInt32(dr["Likes"]) : 0,

#2

You need to change your types to Nullable types.

您需要将类型更改为Nullable类型。

Change (int)dr["Likes"] to (int?)dr["Likes"]
and Datetime = (DateTime)dr["Datetime"] to Datetime = (DateTime?)dr["Datetime"].

将(int)dr [“Likes”]更改为(int?)dr [“Likes”]和Datetime =(DateTime)dr [“Datetime”]到Datetime =(DateTime?)dr [“Datetime”]。

You will also need to update your model coments to allow for nullable types.

您还需要更新模型coments以允许可以为空的类型。

Microsoft Nullable Types.

Microsoft Nullable Types。

#1