Question

When reading data from ExecuteReader. It returns me data in IDataReader. When I want to fill this data into my entities I will be assigning Non Nullable values in most of the cases to either Nullable types or Non Nullable types, e.g.:

int id;
string name;
int? age;
byte[] image;

example e = new example();
e.id = (int)dr["id"]; //unbox
e.name = dr["name"].ToString() //will result in empty string if dr["name"] is DBNull
e.name = dr["name"] is DBNull ? null : dr["name"].ToString();
e.age = dr["age"] as int?; // way 1
e.age = dr["age"] is DBNull ? null : (int?)dr["age"]; //way 2
e.image = dr["image"] as byte?;

EDIT

if id is primary key for the table and is NonNullable. But it is being used in another table where this key could be NULL then what should be the approach. Should that entity become NULL or exception should be thrown.

Answer 1

If the object reference is null, the is operator always returns false because there is no object available to check its type.

if (o is Employee) {
Employee e = (Employee) o;
// Use e within the ‘if’ statement.
}

The as operator works just like casting except the as operator will never throw an exception. Instead, if the object can’t be cast, the result is null.

Employee e = o as Employee;
if (e != null) {
// Use e within the ‘if’ statement.
}

Check more : C# is and as operators