Factory pattern or "convention over ifs"?

1_without_factory_pattern.java

// example from book "Head First Design Patterns".

// without factory pattern
public class PizzaStore {
 
	public Pizza orderPizza(String type) {
		Pizza pizza;

                // bad! we have a lot of ifs here...
		if (type.equals("cheese")) {
			pizza = new CheesePizza();
		} else if (type.equals("pepperoni")) {
			pizza = new PepperoniPizza();
		} else if (type.equals("clam")) {
			pizza = new ClamPizza();
		} else if (type.equals("veggie")) {
			pizza = new VeggiePizza();
		}
 
		pizza.prepare();
		pizza.bake();
		pizza.cut();
		pizza.box();

		return pizza;
	}

}

2_implementing_factory_pattern.java

// example from book "Head First Design Patterns".

public class PizzaStore {
	SimplePizzaFactory factory;
 
	public PizzaStore(SimplePizzaFactory factory) { 
		this.factory = factory;
	}
 
	public Pizza orderPizza(String type) {
		Pizza pizza;
 
                // good! (or bad?) now we have another class to decide what pizza should be created...
		pizza = factory.createPizza(type);
 
		pizza.prepare();
		pizza.bake();
		pizza.cut();
		pizza.box();

		return pizza;
	}

}


public class SimplePizzaFactory {

	public Pizza createPizza(String type) {
		Pizza pizza = null;

                // Oh ok! But we still having many ifs... Is it good?
		if (type.equals("cheese")) {
			pizza = new CheesePizza();
		} else if (type.equals("pepperoni")) {
			pizza = new PepperoniPizza();
		} else if (type.equals("clam")) {
			pizza = new ClamPizza();
		} else if (type.equals("veggie")) {
			pizza = new VeggiePizza();
		}
		return pizza;
	}
}

3_convention_over_factory_pattern.rb

class PizzaStore

  def order_pizza pizza_type

    # and what happens if I decide to use some "convention over ifs" here? It's a good or bad idea?
    pizza = eval(pizza_type.constantize).new

    pizza.prepare
    pizza.bake
    pizza.cut
    pizza.box

    pizza
  end

end