从数据库读取数据导致无法将类型为“ System.Byte”的对象转换为类型为“ System.String”的错误

Question

Please see the case 1 and 2 below.

In case 2 : reader.GetString(reader.GetOrdinal("dmic_only")) line return "1" successfully

In case 1 : same code part in string.IsNullOrEmpty( reader.GetString(reader.GetOrdinal("dmic_only")) ) == false throws exception.

Exception : Unable to cast object of type 'System.Byte' to type 'System.String'.

dmic_only is a tinyint in database, not byte. It is really interesting. What is difference in cases?

Case 1:

 if ((!reader.IsDBNull(reader.GetOrdinal("dmic_disallowed")) 
 && string.IsNullOrEmpty(reader.GetString(reader.GetOrdinal("dmic_disallowed"))) == false)
 && (!reader.IsDBNull(reader.GetOrdinal("dmic_only")) 
 && string.IsNullOrEmpty(reader.GetString(reader.GetOrdinal("dmic_only"))) == false))
{
   retVal.Add("dmic_disallowed", reader.GetString(reader.GetOrdinal("dmic_disallowed")));
   retVal.Add("dmic_only", reader.GetString(reader.GetOrdinal("dmic_only")));
}

Case 2 :

 //if ((!reader.IsDBNull(reader.GetOrdinal("dmic_disallowed")) 
 //&& string.IsNullOrEmpty(reader.GetString(reader.GetOrdinal("dmic_disallowed"))) == false)
 //&& (!reader.IsDBNull(reader.GetOrdinal("dmic_only")) 
 //&& string.IsNullOrEmpty(reader.GetString(reader.GetOrdinal("dmic_only"))) == false))
 //{
   retVal.Add("dmic_disallowed", reader.GetString(reader.GetOrdinal("dmic_disallowed")));
   retVal.Add("dmic_only", reader.GetString(reader.GetOrdinal("dmic_only")));
 //}

Answer 1

The exception you are getting is telling you exactly what you need to know...

reader.GetString(reader.GetOrdinal("dmic_only")) // will throw an error 

as you have said dmic_only is a tinyint

if you really want it as a string, you will have to unbox it first as a byte then to a string

string strValue = Convert.ToString((byte)reader["dmic_only"))