Question

I am new to design patterns. I am looking for a pattern similar to the factory pattern but that will also let me “set” the product. Something like this:

class VehicleFactory
{
    IVehicle static GetVehicle();
    void static SetVehicle(IVehicle vehicle);
}

Is there any known pattern similar to this? Thank you.

EDIT: I am looking to store “POCO” objects in the Session object and use a class to set/ get them. I may want to switch persistance to ViewState/ database in the future. This is what I have:

// object to persist in Session.
class Vehicle
{
    string Make { get; set; }
    string Model { get; set; }
}

// class to set/ get object from Session.
// Please see VehicleFactory above.

Answer 1

Factory pattern is a creational design pattern with encapsulates the creation of a complex object and isolates the creation process from your business logic.

Here it looks like you want a cache to store and manage the Vehicle instances. I would recommend that you call this class a VehicleCache rather than Factory and implement like a cache.

Firstly you should consider having and identifier for the Vehicle object like a vehicleId. I would also recommend that you implement it as an entity object as described in Domain Driven Design.

Then you can implement your cache like this –

public class VehicleCache
{
    public void Add(IVehicle instanceToAdd)
    {
    // Store instance in session object
    }

    public IVehicle Get(string id) 
    {
     // search and return vehicle from cache
    }

    // more methods and indexer if required
}

Here are some links that explain how you can implement such cache for your application in a thread safe fashion –

https://blogs.infosupport.com/blogs/frankb/archive/2008/12/31/Implementing-a-Thread-Safe-cache-using-the-Parallel-Extensions.aspx

http://www.objectreference.net/post/Implementing-Generic-Caching.aspx