无法投类型的对象'System.DBNull'输入'System.String` [英] Unable to cast object of type 'System.DBNull' to type 'System.String`

问题描述

我在我的应用程序得到了上述错误。原来这里是code

I got the above error in my app. Here is the original code

public string GetCustomerNumber(Guid id)
{
     string accountNumber = 
          (string)DBSqlHelperFactory.ExecuteScalar(connectionStringSplendidmyApp, 
                          CommandType.StoredProcedure, 
                          "GetCustomerNumber", 
                          new SqlParameter("@id", id));
     return accountNumber.ToString();
 }

我换成

public string GetCustomerNumber(Guid id)
{
   object accountNumber =  
          (object)DBSqlHelperFactory.ExecuteScalar(connectionStringSplendidCRM, 
                                CommandType.StoredProcedure, 
                                "spx_GetCustomerNumber", 
                                new SqlParameter("@id", id));
    if (accountNumber is System.DBNull)
    {
       return string.Empty;
    }
    else
    {
       return accountNumber.ToString();
    }
}

有没有解决这个更好的办法？

Is there a better way around this?

推荐答案

一个较短的形式，可以用：

A shorter form can be used:

return (accountNumber == DBNull.Value) ? string.Empty : accountNumber.ToString()

编辑：有没有重视的ExecuteScalar。它真的返回null如果该字段是返回结果缺席。所以改用：

Haven't paid attention to ExecuteScalar. It does really return null if the field is absent in the return result. So use instead:

return (accountNumber == null) ? string.Empty : accountNumber.ToString() 

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