Verify if a value is a DBNull

Question

I'm using the mySql connector with phpMyadmin and i try to verify if a value is a DBNull cause it make my project bug and I didn't succeed to find a way to verify it.

I tried:if( aReader.GetString("ColumnName") != DBNull.value){...} but it doesn't work.

I have this error:

System.InvalidCastException: 'Unable to cast object of type 'System.DBNull' to type 'System.String'.'

the code i made is :

MySqlDataReader aReader = aMySqlCommand.Command.ExecuteReader();
while(aReader.Read())
{
    aReader.GetString("columnName"); // there's the place where I get my error
}

thanks for you answer

https://dev.mysql.com/doc/dev/connector-net/8.0/html/T_MySql_Data_MySqlClient_MySqlDataReader.htm — Asteroids With Wings, Jun 15 '20 at 17:24
More specifically: [the IsDBNull method](https://dev.mysql.com/doc/dev/connector-net/8.0/html/M_MySql_Data_MySqlClient_MySqlDataReader_IsDBNull.htm) — stuartd, Jun 15 '20 at 17:26

score 1 · Accepted Answer · answered Jun 15 '20 at 17:27

1

MySqlDataReader has a method to check for null: reader.IsDBNull(index). https://learn.microsoft.com/en-us/dotnet/api/system.data.sqlclient.sqldatareader.isdbnull?view=dotnet-plat-ext-3.1

answered Jun 15 '20 at 17:27

Jacob Huckins

368
2
15

score 0 · Answer 2 · answered Jun 15 '20 at 17:34

0

Check if value is null. do different things depending on if it's actually null or not.

if(Convert.IsDBNull(aReader["columnName"])) {
  //do things if null
} else {
  aReader.GetString("columnName");
}

answered Jun 15 '20 at 17:34

Mikael

1,002
1
11
22

thank you for your answer, it worked well! – BenBel Jun 16 '20 at 18:19

Verify if a value is a DBNull

2 Answers2