How do I retrieve a data type of tinyint from MySQL in C#?

To determine the proper type, look at the value of

reader["MyField"].GetType()

in the debugger.

The problem is that due to casting and explicit operators:

(byte)objectExpression is is not the same as (byte)sbyteExpression.

The first is a [direct] cast which fails because the real object type is sbyte and not byte. The latter will perform a conversion that just happens to use a explicit operator (an "Explicit Conversion") with syntax that, unfortunately, still looks like a [direct] cast as per above. Here is an example of it failing sans-database:

var obj = (object)(sbyte)0;
var i1 = (int)(sbyte)obj;  // okay: object (cast)-> sbyte (conversion)-> int
var i2 = (int)obj;         // fail: sbyte (cast)-> int (but sbyte is not int!)

Either use an (sbyte)objectExpression cast which is valid for the real object type, or Convert.ToInt32(objectExpression) which takes an object and does some magic to convert it to an int. (Using Convert.ToByte could throw an exception on overflow.)

Happy coding!