如果条件检查DBNull.Value

Question

I'm trying to check for DBNull.Value but in this case reader["Preferences"] returns {} in the immediate window (why?)

so when (string)reader["Preferences"]; executes I get a type casting error

if (reader["Preferences"] == System.DBNull.Value)
{
     preferences = (string)reader["Preferences"];
}

Answer 1

You are trying to cast only when the value is DBNull.Value .

You should invert your if :

if (reader["Preferences"] != System.DBNull.Value)
{
     preferences = (string)reader["Preferences"];
}