I am writing a program that synchronizes playlists among different streaming services, the problem is every service uses different structures and functions.
I want to make it "modular" so i can add new services and syncronize them with the others without programming them for every service i have already in the application and the best idea i came out with is to implement it by using a sort of intermediate language (or intermediate models), e.g.
namespace Service1
{
class Service1Album
{
public string ID { get; set; }
public Service1Artist Artist { get; set; }
//Some other props...
public IntermediateAlbum ToIntermediate()
{
//conversion...
}
}
class Service1Artist
{
//Some props...
public string ID { get; set; }
public IntermediateArtist ToIntermediate()
{
//conversion...
}
}
}
namespace Intermediate
{
class IntermediateArtist
{
//Props that every service has in common...
}
class IntermediateAlbum
{
//Props that every service has in common...
}
}
In this way every service I implement accept as parameter for its functions Intermediate models and outputs his own models that can be converted.
Service1Album album = service1.GetAllAlbums()[0];
IntermediateAlbum intermediateAlbum = album.ToIntermediate();
service2.AddAlbum(intermediateAlbum);
service3.AddAlbum(intermediateAlbum);
Is there a way I can implement this more elegantly? And if so, is there a way I can inherit every service from something like a ServiceContainer that abstracts every service like this?
var sList = new List<ServiceContainer>{};
sList.Add(new Service1());
sList.Add(new Service2());
foreach (var service in sList)
{
service.addAlbum(new IntermediateAlbum()
{
//properties
});
}
Luca - Welcome! You're discovering the need for some design patterns in your code. That's really great - it means things are getting complex enough that you can start to lean on the patterns others have spent years refining in building your solution.
#1 - Switch to using Interfaces + Design Patterns
If I were you, I'd start by abstracting everything to interfaces (eg - you'd run your work in each Service against IAlbum's and IArtist's instead of concrete implementations).
Then, once your interfaces are in place, take a look at the .net code for the gang-of-four patterns to figure out how to layout the work.
#2 - The basics
There's a lot of code to write, but the skeleton might end up looking like this
namespace MusicService
{
public interface IAlbum {
//common album properties/methods
}
public interface IArtist {
//common artist properties/methods
}
internal abstract class AlbumBase:IAlbum {
// implement common functions and properties if you have them...
// otherwise, skip this
}
internal abstract class ArtistBase:IAlbum {
// implement common functions and properties if you have them...
// otherwise, skip this
}
}
namespace MusicService.AppleMusic
{
internal class Album:AlbumBase
{ //OR Album:IAlbum if you skipped that AlbumBase thing
//code apple music specific stuff here ...
// think of this as a "mask" that the apple album is
// wearing so that it can pretend to be an iAlbum
}
internal class Artist:ArtistBase
{
//same comments apply here
}
}
namespace MusicService.Spotify
{
internal class Album:AlbumBase
{
//GO and do liekwise with Spotify
}
internal class Artist:ArtistBase
{
//GO and do liekwise with Spotify
}
}
#3 - Implementing the actual SYNC
Now that you have the code you need for your various music services (neatly arranged, so your fellow programmers don't have to dig through your brain to figure out what you were thinking), you can code your SyncService.
I don't want to spoil the fun (sync service could use the decorator pattern or it could be a sort of composite -- not sure what your sync code needs to do), but your final sync code could be as easy as:
var myService = new SyncService();
myService.AddAppleMusic();
myService.AddSpotify();
myService.Sync();
Spoiling the Fun
OK. Fine. Here's what I'd do.
namespace MusicService {
public interface IService {
//propably a List<IAlbum> and List<IA> somewhere in here
void Sync();
}
public class SyncService {
internal List<IService> _services;
public void AddService(IService musicService) {
if(_services==null){_services=new List<IService>();}
_services.Add(musicService);
}
public void Sync() {
foreach(IService ms in _services) {
ms.Sync();
}
}
}
}
namespace MusicService.AppleMusic {
internal AppleSyncService:IService {
public AppleSyncService() {
//Do your apple-specific initializations here
}
public void Sync() {
//apple-sync
}
}
internal class ExtendService(){
public static void AddAppleMusic(this SyncService syncAgent) {
syncAgent.AddService(new AppleSyncService());
}
}
}
Obviously - none of that code compiles, and coding in notepad is probably a bad idea. But, it gives you a pattern-based alternative to your sample code above. AND - if you add a third music service, you don't run the risk of breaking apple and spotify just to wedge in that new one!
Good luck. Sounds like a fun project.
Related
I have a somewhat basic design question that I have not been able to find a good answer to (here, on other forums nor the books I've consulted)
I'm creating a dll and is wondering what the best way to expose its content would be. I'm aiming for a single point of entry for the apps using the dll.
The solution should adhere to the Dependency Inversion Principle (DIP) which would imply the use of an interface. But here is the kicker: the functionality of the dll requires an object to be instantiated and there must only be almost one instance at any time (kinda like a singleton though the thought sends shivers down my spine) It is this fact that I would like to spare the users of the DLL from knowing about.
Some code to explain what I would like to be able to do:
The dll:
namespace MyQuestionableDll
{
interface IMyQuestionableDll
{
public static IMyQuestionableDll Instance; // This is not allowed which makes sense
public void PressTheRedButton();
}
internal class QuestionableImplementation : IMyQuestionableDll
{
public void PressTheRedButton()
{
// Distribute Norwegian Black Metal at local school
}
}
}
And the use case:
using MyQuestionableDll;
class UnluckyAppThatIsForcedToUseQuestionableDlls
{
static void Main(string[] args)
{
IMyQuestionableDll questionableInstance = IMyQuestionableDll.Instance; // Again not allowed which still makes sense
questionableInstance.PressTheRedButton();
// or simply
MyQuestionableDll.Instance.PressTheRedButton();
}
}
An abstract class could be part of the answer but it then starts to feel like not following the DIP anymore.
Any great design insights, knowledge of best practices when making dlls or recommendations regarding Norwegian Black Metal?
If the explanation is too vague I will gladly elaborate on it.
Cheers!
- Jakob
I could imagine a two-factor approach:
A factory interface (that will create/return an instance of ...)
The API interface
For Example:
public interface IMyApiFactory
{
IMyAPI GetInstance();
}
public interface IMyAPI
{
// Whatever your API provides
}
This way you have the complete control inside your dll about how to create and reuse instances (or not).
A similar way would be some kind of Builder-Pattern:
public interface IMyApiBuilder
{
IMyApi Build();
}
public interface IMyApi
{
void PressTheRedButton();
// Whatever it does else
}
public sealed class MyAPI : IMyApi, IMyApiBuilder
{
public static IMyApiBuilder Builder = new MyAPI();
private MyAPI()
{
// CTOR ...
}
// vv Notice _explicit_ interface implemenations.
// https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/interfaces/explicit-interface-implementation
IMyApi IMyApiBuilder.Build() { return this; }
void IMyApi.PressTheRedButton()
{
// ...
}
}
// USAGE:
IMyApi api = MyAPI.Builder.Build();
Thank you so much Fildor and ema! The ideas of adding a factory method, a factor interface or even a full-blown builder is definitely good solutions! And it got me thinking about how to incorporate them into my DLL while still sparing its users. They don't need to know that it in fact is a foul smelling factory with polluting smokestack emissions that are creating the instance :)
Then I came across Default Interface Methods and the structure of my approach ended up being
public interface MyQuestionableDll
{
static readonly MyQuestionableDll Instance = new QuestionableImplementation();
void PressTheRedButtonBelowTheDoNotPushSign();
}
internal class QuestionableImplementation : MyQuestionableDll
{
public void PressTheRedButtonBelowTheDoNotPushSign()
{
// Distribute German Volksmusik at local school
}
}
// and the use case
var questionableInstance = MyQuestionableDll.Instance;
questionableInstance.PressTheRedButtonBelowTheDoNotPushSign();
Thanks again Fildor and ema!
- Jakob
There is something I do not understand about open-close principle. Let's say that you have done this code:
public abstract class Player
{
public string Name { get; set; }
public int Level { get; set; }
}
public sealed class Fighter : Player { /* ... */ }
public sealed class Warrior : Player { /* ... */ }
This code works perfectly, you've done a first release, eveyrthing is OK.
Now you want to add some features, like a player can equip a ring. Open-close principle says open to extension, close to modification. How could I implement the fact that my players can have rings if I shouldn't modify these class?
You can modify class Player by adding new methods and fields. It is open to extension. But if you already have some methods like Jump or Fight and you want to modify them - that is breaking the principle.
Imagine, your class Fighter has method Fight() and it uses only bare hands:
public Fighter() : Player
{
...
public virtual void Fight()
{
//use bare hands
}
}
If you want Fighter to fight with a stick (for example) you should not modify initial method Fight() but add another class like FighterWithStick : Fighter and override method Fight() there:
public FighterWithStick() : Fighter
{
...
public override void Fight()
{
//use stick
}
}
First think why this kind of rule might be useful. Closed to modification, open to extension. This makes sense for libraries or code that must be backwards compatible. Think of this example:
I've written "BestLibrary" library which exposes interface:
namespace BestLibrary
{
public interface GoodStuff
{
Goodies GiveMeGoodStuff();
}
}
But in the next release I want to decide what Goodies to give based on a parameter, so I change the interface to:
namespace BestLibrary
{
public interface GoodStuff
{
Goodies GiveMeGoodStuff(GoodiesType type);
}
}
public enum GoodiesType { All, Type1, Type2 }
Now everyone who uses my library has to fix their code, because their projects will stop building. This brakes Open/Closed principle. Instead I should make another method, like this:
namespace BestLibrary
{
public interface GoodStuff
{
Goodies GiveMeGoodStuff();
Goodies GiveMeGoodStuff(GoodiesType type);
}
}
Here I didn't modify anything. Old code still works. Someone wants random Goodies? They can still get it. I extended GoodStuff interface with additional method. This way everything compiles and people can use new functionality.
If you work on a project that is not a library or api, then I don't see any reason to follow this principle. Requirements change and code should follow.
I want to integrate my application with X number of external systems. The integration with each external system will have same kind of actions but will be handled in a separate classes.
Hence the aim to define an interface that will make sure all integration classes conform to certain actions. e.g.
public interface IOrderIntegration
{
//I want to define the ImportOrder action here, so that all future integrations conform
}
However each external system has its own closed SDK (cannot be edited) that needs to be referenced. e.g
public class EbayOrderIntegration : IOrderIntegration
{
void ImportOrder(Ebay.SDK.Order order)
{
//Logic to import Ebay's order
}
}
public class AmazonOrderIntegration : IOrderIntegration
{
void ImportOrder(Amazon.SDK.Order order)
{
//Logic to import Amazon's order
}
}
Is there a way to still use an interface in this case to ensure all integrations perform a certain action? Or perhaps another pattern ?
This is where generics come intp play:
public interface IOrderIntegration<T>
{
void ImportOrder(T order);
}
public class EbayOrderIntegration : IOrderIntegration<Ebay.SDK.Order order>
{
void ImportOrder(Ebay.SDK.Order order order)
{
// ...
}
}
Another way than HimBromBeere's answer (great answer by the way !). Note that this can only work if you can abstract at the order level:
public class OrderIntegration
{
public void ImportOrder(IOrder order)
{
// Only possible if you can abstract all the logic into IOrder
}
}
public interface IOrder
{
// Abstract here the order logic
}
public class EbayOrder : IOrder
{
public EbayOrder(Ebay.SDK.Order order)
{ .. }
}
public class AmazonOrder : IOrder
{
public AmazonOrder(Amazon.SDK.Order order)
{ .. }
}
The choice between HimBromBeere's anwser and mine will depend on where you want to (and can!) abstract your different providers and how you want to use your API.
I want my site to support different subscription types, free, premium and etc.
So far I made an abstract class that is like this
public abstract class Limits
{
public int PostLimit { get; protected set; }
protected Limits(int postLimit)
{
PostLimit = postLimit;
}
public bool IsLimitReached(int postCount)
{
return postCount > PostLimit
}
}
public class FreeLimit : Limits
{
private const int postLimit = 1;
public FreeLimit()
: base(postLimit)
{
}
}
So now I did this for all my account types. Now the problem is I don't know how to actually use this class.
For instance I have a service layer call PostService and in this class I have
public void CreatePost(Post post)
{
// do stuff here
}
Now in this method I don't know how to check if they reached the limit. I don't know how to check because I am unsure how to find out if I should be using the FreeLimit or PremiumLimit or what account they have.
I am thinking that I first have to figure out their Role and then somehow use that information to create the right class.
I guess I could have something like
public void CreatePost(Post post, PlanType planType)
{
Limits limit;
switch(planType)
{
case planType.Free:
limit = new FreeLmit()
break;
}
if(limit.IsLimitReached())
{
// do stuff
}
}
I don't like this way as now for every method that needs to check a limit will have to do this. I will have a few methods that require this check in my service layer.
So I was thinking of putting it in my constructor but I don't know if it is good to have a switch statement in a constructor.
You could use an interface ILimit
interface ILimit
{
int PostLimit { get; protected set; }
bool IsLimitReached(int postCount);
}
Now you can have several other classes (Free, Premium, Super) that implement this interface. In your service method CreatePost you can just pass any instance of a class that implements the interface and use it - there's no need to distinguish them anymore since they all support the same interface.
public void CreatePost(Post post, ILimit limit)
{
if(limit.IsLimitReached())
{
// do stuff
}
}
Well, the Limit property is tied to what entity? I suppose it's tied to the Blog (or maybe a Forum) and it is persisted on a DB or something else.
If so, you can do something like this:
public void CreatePost(Post post)
{
if(post.Blog.IsLimitReached())
{
// do stuff
}
}
The Blog.IsPostLimitReached() should call this.Limit.IsLimitReached from itself.
I hope you can understand what I said :)
If you have different types of user, you can tie their accounts (once they've logged in) to different RoleTypes. Then you can use HttpContext.Current.User.IsInRole("RoleName") to see if they are in a specific role, and use that as your basis for showing/hiding functionality.
I have a set of DataContracts that are serialzed through WCF.
Please note this is a very simplified example.
[DataContract]
public class MyData
{
[DataMember]
public List<int> MyList
{
get;
set;
}
}
I would like to use object oriented design so that the server and client aren't creating any unnecessary dependencies. For example, I would like to encapsulate a list so that the user can't directly modify it.
Ideally, I would like the class to look like this if it wasn't a DTO.
public class MyData
{
private List<int> _list = new List<int>();
public IEnumerable<int> MyList
{
get
{
return _list;
}
}
public void AddItem( int value )
{
_list.Add( value );
}
}
I am using the same C# assembly from both the service and the client. So I can add non-DataMember methods, but I'm not sure if that is a good approach. It doesn't smell quite right to me.
Does anybody have a clever way of treating DTO classes more like objects instead of simple serializable structures?
How about having DTO versions of your logic class which are used solely for the purpose of message passing?
That way, you can put all the methods and properties on your logic class as necessary without having to worry about what the user has access to when it's passed over the wire. There are many ways you can go about this, for instance:
you can implement some method on your logic class to return the DTO
public class Player
{
// methods that do interesting things here
...
public string Name { get; set; }
public PlayerDTO ToTransport()
{
return new PlayerDTO { Name = Name, ... };
}
}
[DataContract]
public class PlayerDTO
{
[DataMember]
public string Name { get; set; }
...
}
Or you can implement an explicit/implicit conversion
public class Player
{
// methods that do interesting things here
...
public string Name { get; set; }
}
[DataContract]
public class PlayerDTO
{
[DataMember]
public string Name { get; set; }
...
public static explicit operator PlayerDTO(Player player)
{
return new PlayerDTO { Name = player.Name, ... };
}
}
this lets you cast a Player object to PlayerDTO:
var player = new Player { Name = .... };
var dto = (PlayerDTO) player;
Personally, I do think having DataContract on objects which are for more than service operations is a bit of a smell, just as it would be for ORM column mappings. One somewhat limited way to make these DTOs more like true OO is to have your methods be extension methods of the DTO. You might need to do something creative if the OO version has state that needs to be captured between calls that is not inherent in the DTO object itself, though.
I do not think having methods unadorned by attributes in your DataContract's class necessarily smells. You have your service-oriented concerns on one hand (the operation and data contracts) and your object-oriented concerns on the other. What the client does with the provided data is of no concern to the service. The object-oriented issue you describe really only exists for the client.
If a client obtained Ball data from your service and it wants to Draw() it to the screen, whether or not the Ball class has a Draw() method has nothing to do with the contract between service and client. It is a contract between the api your assembly provides and those that use it. So I say, why not have a method in the assembly that is not an operation/data contract?