Question

I was feeling quite clever as I worked out how to create subclasses in C# for an ASP.NET project, then I found a problem – I didn’t know how to create an object of the right subclass based on the results of a SQL query.

Say you have a class called Animal and two subclasses called Zebra and Elephant. You get the idea?

What I want to do is perform a SQL query and if the row returned has row[“Type”]=”Zebra” then load a Zebra object (or if it’s an Elephant then..).

So, in principle, the Animal class would have a static method:

class Animal{
 public static Animal Load(DataRow row){
  if (row["Type"]=="Zebra"){
   return new Zebra();
  } 
}

class Zebra : Animal{
 //some code here
}

Is this at all possible or have I just plain got the idea of subclasses wrong. It should be obvious I’m no OO expert.

Thanks in advance,
Jake

Answer 1

You can implement the method factory pattern.
http://en.wikipedia.org/wiki/Factory_method_pattern