I am trying to structure my code so that I can easily extend it in the future, however I think I am overthinking things and struggling to accomplish this.
My scenario is:
Based upon some data being passed to me I need to generate a class.
The class that I need to generate is not similar in nature to any of the other classes.
For example I have several classes that can be created:
public class File1{
public string Name {get;set;}
// etc...
}
public class File2{
public int ID {get;set;}
// etc...
}
public class File3{
public string MyType {get;set;}
// etc...
}
In my main class I have:
switch (myExtension)
{
case ".abc":
ProcessABC(myContents);
break;
case ".def":
ProcessDEF(myContents);
break;
case ".ghi":
ProcessGHIL(myContents);
break;
//etc...
}
I have tried creating an interface with a common method:
public ProccessStuff(data);
but I don't think that will work since I don't have a common return type.
Then I thought about an abstract class, but then it seems I'll be pushing a lot of work into that abstract class.
public abstract class MyAbstractClass
{
public void ProcessStuff(string data)
{
// Parse the data into an object
// Update some DB fields
// Log some data
}
}
Am I on the right path with just creating an abstract class to handle all of my logic?
You're saying the classes don't have any similarities. But that's not actually true - they all take a string to do some processing, and it's exactly this that you want shared between the classes.
Make an interface, IDataProcessor (or something). There, have a single method - void Process(string). The file classes will implement the method in a way they require.
This changes your main classes switch to a simple
IDataProcessor actualDataProcessor = ...;
actualDataProcessor.Process(myContents);
Of course, you still need some way to create the proper IDataProcessor based on e.g. the extension. Depending on your exact needs, a simple Dictionary<string, Func<IDataProcessor>> might be quite enough. Otherwise, there's plenty of other ways to bind classes more dynamically if you so desire, or use an explicit factory class.
Have you tried using generics?
Here is an example :
public void Process<T>(string contents)
where T : IProcessStuff, new ()
{
// Common work to do here
// ...
// Specific processing stuff
T t = new T();
t.ProcessStuf(contents);
}
public interface IProcessStuff
{
void ProcessStuf(string contents);
}
Related
I have a business requirement to consolidate CRUD operations into a single base class, regardless of the type of object. I am not able to modify the calling code, which could be anything ... so if there are a bunch of callers that look like this:
var state = new State("New York");
state.Save();
var city = new City("New York", state);
city.Save();
var stadium = new Stadium("Yankee Stadium", city);
stadium.Save();
All of these Save methods would need to be handle in one, single common base class.
The path I've lead myself down is to create a single generic abstract base class which these classes implement, such as the following ...
public abstract class PersistableObject<T> where T : class {
public string Id { get; set; }
public static T Find(string id) {}
public void Save() { }
public void Delete() { }
}
I then have the above objects inherit from this class:
public class City: PersistableObject<City> { }
I stripped out the CRUD methods tied to the concrete implementations and after having these various objects inherit from the abstract base class, the solution compiles without error.
And now I'm stuck. The backing store is a local XML document (decision out of my hands). I am guessing I can serialize these to XML using the normal XML serializers in .Net, but is there a better way to do this? Should I be using some sort of a repository pattern?
Thanks.
I am making a payment system for my site. Users can select one of several payment providers to pay, but all should behave in the same way. I thought to represent this behavior like this:
public abstract class PaymentProvider {
private static var methods = Dictionary<String,PaymentProvider>
{
{"paypal",new PaymentProviderPaypal()},
{"worldpay",new PaymentProviderWorldpay()}
}
public static Dictionary<String,PaymentProvider> AllPaymentProviders
{
get {return methods;}
}
public abstract pay();
}
public class PaymentProviderPaypal : PaymentProvider {
public override pay() {
}
}
public class PaymentProviderWorldpay : PaymentProvider {
public override pay() {
}
}
You are supposed to use this by writing PaymentProvider.AllPaymentProviders["key"].pay(). The idea is that the functions using this class don't need to know about how the underlying payment provider is implemented, they just need to know the key.
However, at the moment, if you have access to the PaymentProvider class, you also have access to the inheriting classes. Its possible to instantiate a new copy of the inheriting classes, and make use of them in an unexpected way. I want to encapsulate the inheriting classes so that only the abstract PaymentProvider knows about them.
How should I do this? Different protection levels like protected don't work here - In Java, protected means that only other classes in the namespace can use that class, but in C# it means something else.
Do I have the right idea here? Or should I use a different method?
A couple of options spring to mind:
Put this in a separate assembly from the client code, and make the implementations abstract
Put the implementations inside the PaymentProvider class as private nested classes. You can still separate the source code by making PaymentProvider a partial class - use one source file per implementation
The first option is likely to be the cleanest if you don't mind separating the clients from the implementation in terms of assemblies.
Note that both of these are still valid options after the change proposed by Jamiec's answer - the "visibility" part is somewhat orthogonal to the inheritance part.
(As an aside, I hope the method is really called Pay() rather than pay() :)
Your inheritance heirachy is a bit wonky, I would be tempted to do it a similar but crucially different way.
public interface IPaymentProvider
{
void Pay()
}
// Implementations of IPaymentProvider for PaypalPaymentProvider & WorldpayPaymentProvider
public static class PaymentHelper
{
private static var providers = Dictionary<String,IPaymentProvider>
{
{"paypal",new PaymentProviderPaypal()},
{"worldpay",new PaymentProviderWorldpay()}
}
public static void Pay(string provider)
{
if(!providers.Containskey(provider))
throw new InvalidOperationException("Invalid provider: " + provider);
providers[provider].Pay();
}
}
Then the usage would be something like PaymentHelper.Pay("paypal").
Obviously if there is more data to provide to the Pay method this can be added to both the interface, and the helper. for example:
public interface IPaymentProvider
{
void Pay(double amount);
}
public static void Pay(string provider, double amount)
{
if(!providers.Containskey(provider))
throw new InvalidOperationException("Invalid provider: " + provider);
providers[provider].Pay(amount);
}
I have a fairly simple system, and for the purposes of this question there are essentially three parts: Models, Repositories, Application Code.
At the core are the models. Let's use a simple contrived example:
public class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
}
In that same project is a generic repository interface. At its simplest:
public interface IRepository<T>
{
T Save(T model);
}
Implementations of that interface are in a separate project and injected with StructureMap. For simplicity:
public class PersonRepository : IRepository<Person>
{
public Person Save(Person model)
{
throw new NotImplementedException("I got to the save method!");
// In the repository methods I would interact with the database, or
// potentially with some other service for data persistence. For
// now I'm just using LINQ to SQL to a single database, but in the
// future there will be more databases, external services, etc. all
// abstracted behind here.
}
}
So, in application code, if I wanted to save a model I would do this:
var rep = IoCFactory.Current.Container.GetInstance<IRepository<Person>>();
myPerson = rep.Save(myPerson);
Simple enough, but it feels like it could be automated a lot. That pattern holds throughout the application code, so what I'm looking to do is create a single generic Save() on all models which would just be a shorthand call to the above application code. That way one would need only call:
myPerson.Save();
But I can't seem to figure out a way to do it. Maybe it's deceptively simple and I'm just not looking at it from the correct angle. At first I tried creating an empty ISaveableModel<T> interface and intended to have each "save-able" model implement it, then for the single generic Save() method I would have an extension on the interface:
public static void Save<T>(this ISaveableModel<T> model)
{
var rep = IoCFactory.Current.Container.GetInstance<IRepository<T>>();
model = rep.Save(model);
}
But it tells me that rep.Save(model) has invalid arguments. It seems that it's not wiring up the type inference as I'd hoped it would. I tried a similar approach with a BaseModel<T> class from which models would inherit:
public class BaseModel<T>
{
public void Save()
{
this = IoCFactory.Current.Container.GetInstance<IRepository<T>>().Save(this);
}
}
But the compiler error is the same. Is there a way to achieve what I'm trying to achieve? I'm very flexible on the design, so if I'm going about something all wrong on an architectural level then I have room to step back and change the big picture.
Would a generic extension method solve it?
public static T Save<T>(this T current)
{
var rep = IoCFactory.Current.Container.GetInstance<IRepository<T>>();
rep.Save(current);
}
You can then constrain it to your ISaveableModel<T> interface. Return type above not implemented, but you can put it to a boolean or status flag, whatever.
In both approaches, the parameter to the Save() function is not of type T. In the first one, it is ISaveableModel<T>, and in the second, it is BaseModel<T>. Since the repository is a generic based on T, Save method will expect a variable of type T. You can add a simple cast to T before you call Save to fix it.
Alternatively, your IRepostory<T> can be changed to
public interface IRepository<T>
{
T Save(ISaveableModel<T> model);
}
which makes more sense.
I had a class that had lots of methods:
public class MyClass {
public bool checkConditions() {
return checkCondition1() &&
checkCondition2() &&
checkCondition3();
}
...conditions methods
public void DoProcess() {
FirstPartOfProcess();
SecondPartOfProcess();
ThirdPartOfProcess();
}
...process methods
}
I identified two "vital" work areas, and decided to extract those methods to classes of its own:
public class MyClass {
private readonly MyClassConditions _conditions = new ...;
private readonly MyClassProcessExecution = new ...;
public bool checkConditions() {
return _conditions.checkConditions();
}
public void DoProcess() {
_process.DoProcess();
}
}
In Java, I'd define MyClassConditions and MyClassProcessExecution as package protected, but I can't do that in C#.
How would you go about doing this in C#?
Setting both classes as inner classes of MyClass?
I have 2 options: I either define them inside MyClass, having everything in the same file, which looks confusing and ugly, or I can define MyClass as a partial class, having one file for MyClass, other for MyClassConditions and other for MyClassProcessExecution.
Defining them as internal?
I don't really like that much of the internal modifier, as I don't find these classes add any value at all for the rest of my program/assembly, and I'd like to hide them if possible. It's not like they're gonna be useful/reusable in any other part of the program.
Keep them as public?
I can't see why, but I've let this option here.
Any other?
Name it!
Thanks
Your best bet is probably to use partial classes and put the three clumps of code in separate files adding to the same class. You can then make the conditional and process code private so that only the class itself can access them.
For "Helper" type classes that aren't going to be used outside the current assembly, Internal is the way to go if the methods are going to be used by multiple classes.
For methods that are only going to be used by a single class, I'd just make them private to the class, or use inner classes if it's actually a class that's not used anywhere else. You can also factor out code into static methods if the code doesn't rely on any (non-static) members of your class.
I can
define MyClass as a partial class,
having one file for MyClass, other for
MyClassConditions and other for
MyClassProcessExecution.
Maybe it's my C++ background, but this is my standard approach, though I bundle small helper classes together into a single file.
Thus, on one of my current projects, the Product class is split between Product.cs and ProductPrivate.cs
I'm going for something else - the issue of public / protected / private may not be solved specifically by this, but I think it lends itself much better to maintenance then a lot of nested, internal classes.
Since it sounds like you've got a set of steps in a sequential algorithm, where the execution of one step may or may not be dependent upon the execution of the previous step. This type of sequential step processing can sometimes use the Chain of Responsibility Pattern, although it is morphed a little bit from its original intention. Focussing only on your "processing method", for example, starting from something like below:
class LargeClass
{
public void DoProcess()
{
if (DoProcess1())
{
if (DoProcess2())
{
DoProcess3();
}
}
}
protected bool DoProcess1()
{
...
}
protected bool DoProcess2()
{
...
}
protected bool DoProcess3()
{
...
}
}
Using Chain of Responsibility, this could be decomposed into a set of concrete classes for each step, which inherit from some abstract step class. The abstract step class is more responsible for making sure that the next step is called, if the necessary preconditions are met.
public class AbstractStep
{
public AbstractStep NextStep { get; set; }
public virtual bool ExecuteStep
{
if (NextStep != null)
{
return NextStep.ExecuteStep();
}
}
}
public class ConcreteStep1 : AbstractStep
{
public bool ExecuteStep
{
// execute DoProcess1 stuff
// call base
return base.ExecuteStep();
}
}
...
public class ConcreteStep3 : AbstractStep
{
public bool ExecuteStep
{
// Execute DoProcess3 stuff
// call base
return true; // or false?
}
}
To set this up, you would, in some portion of the code, do the following:
var stepOne = new ConcreteStep1();
var stepTwo = new ConcreteStep2();
var stepThree = new ConcreteStep3();
stepOne.NextStep = stepTwo;
stepTwo.NextStep = stepThree;
bool success = stepOne.ExecuteStep();
This may help clean up the code bloat you've got in your single class - I've used it for a few sequential type algorithms in the past and its helped isolate each step nicely. You could obviously apply the same idea to your condition checking (or build them into each step, if that applies). You can also do some variation on this in terms of passing state between the steps by having the ExecuteStep method take a parameter with a state object of some sort.
Of course, if what you're really concerned about in this post is simply hiding the various steps, then yes, you could make each of your substeps a protected class within your class that creates the steps. Unless you're exposing your library to customers in some form or fashion however, and you don't want them to have any type of visibility into your execution steps, this seems to be a smaller concern then making the code maintainable.
Create the classes with the same access modifier as the methods you have refactored. Partial classes are only really usefull when you have multiple people or automat5ed code generating tools frequently modifying the same classes. They just really avoid source merge hell where your source controll mashes your code because it can't merge multiple edits to the same file.
Yesterday 2 of the guys on our team came to me with an uncommon problem. We are using a third-party component in one of our winforms applications. All the code has already been written against it. They then wanted to incorporate another third-party component, by the same vender, into our application. To their delight they found that the second component had the exact same public members as the first. But to their dismay, the 2 components have completely separate inheritance hierarchies, and implement no common interfaces. Makes you wonder... Well, makes me wonder.
An example of the problem:
Incompatible Types http://www.freeimagehosting.net/uploads/f9f6b862f1.png
public class ThirdPartyClass1
{
public string Name
{
get
{
return "ThirdPartyClass1";
}
}
public void DoThirdPartyStuff ()
{
Console.WriteLine ("ThirdPartyClass1 is doing its thing.");
}
}
public class ThirdPartyClass2
{
public string Name
{
get
{
return "ThirdPartyClass2";
}
}
public void DoThirdPartyStuff ()
{
Console.WriteLine ("ThirdPartyClass2 is doing its thing.");
}
}
Gladly they felt copying and pasting the code they wrote for the first component was not the correct answer. So they were thinking of assigning the component instant into an object reference and then modifying the code to do conditional casts after checking what type it was. But that is arguably even uglier than the copy and paste approach.
So they then asked me if I can write some reflection code to access the properties and call the methods off the two different object types since we know what they are, and they are exactly the same. But my first thought was that there goes the elegance. I figure there has to be a better, graceful solution to this problem.
My first question was, are the 2 third-party component classes sealed? They were not. At least we have that.
So, since they are not sealed, the problem is solvable in the following way:
Extract a common interface out of the coinciding members of the 2 third-party classes. I called it Icommon.
public interface ICommon
{
string Name
{
get;
}
void DoThirdPartyStuff ();
}
Then create 2 new classes; DerivedClass1 and DerivedClass2 that inherit from ThirdPartyClass1 and ThirdPartyClass2 respectively. These 2 new classes both implement the ICommon interface, but are otherwise completely empty.
public class DerivedClass1
: ThirdPartyClass1, ICommon
{
}
public class DerivedClass2
: ThirdPartyClass2, ICommon
{
}
Now, even though the derived classes are empty, the interface is satisfied by the base classes, which is where we extracted the interface from in the first place.
The resulting class diagram looks like this.
alt text http://www.freeimagehosting.net/uploads/988cadf318.png
So now, instead of what we previously had:
ThirdPartyClass1 c1 = new ThirdPartyClass1 ();
c1. DoThirdPartyStuff ();
We can now do:
ICommon common = new DerivedClass1 ();
common. DoThirdPartyStuff ();
And the same can be done with DerivedClass2.
The result is that all our existing code that referenced an instance of ThirdPartyClass1 can be left as is, by just swapping out the ThirdPartyClass1 reference for a ICommon reference. The ICommon reference could then be given an instance of DerivedClass1 or DerivedClass2, which of course in turn inherits from ThirdPartyClass1 and ThirdPartyClass2 respectively. And all just works.
I do not know if there is a specific name for this, but to me it looks like a variant of the adaptor pattern.
Perhaps we could have solve the problem with the dynamic types in C# 4.0, but that would have not had the benefit of compile-time checking.
I would be very interested to know if anybody else has another elegant way of solving this problem.
If you're using .Net 4 you can avoid having to do alot of this as the dynamic type can help with what you want. However if using .Net 2+ there is another (different way) of achieving this:
You can use a duck typing library like the one from Deft Flux to treat your third party classes as if they implemented an interface.
For example:
public interface ICommonInterface
{
string Name { get; }
void DoThirdPartyStuff();
}
//...in your code:
ThirdPartyClass1 classWeWishHadInterface = new ThirdPartyClass1()
ICommonInterface classWrappedAsInterface = DuckTyping.Cast<ICommonInterface>(classWeWishHadInterface);
classWrappedAsInterface.DoThirdPartyStuff();
This avoids having to build derived wrapper classes manually for all those classes - and will work as long as the class has the same members as the interface
What about some wrappers?
public class ThirdPartyClass1 {
public string Name {
get {
return "ThirdPartyClass1";
}
}
public void DoThirdPartyStuff() {
Console.WriteLine("ThirdPartyClass1 is doing its thing.");
}
}
public interface IThirdPartyClassWrapper {
public string Name { get; }
public void DoThirdPartyStuff();
}
public class ThirdPartyClassWrapper1 : IThirdPartyClassWrapper {
ThirdPartyClass1 _thirdParty;
public string Name {
get { return _thirdParty.Name; }
}
public void DoThirdPartyStuff() {
_thirdParty.DoThirdPartyStuff();
}
}
...and the same for ThirdPartyClass2, then you use the wrapper interface in all your methods.
Add an interface. You could add one wrapper (that implements the interface) for each of the 3rd parties.
Anyway, if you have the code of those 3rd parties, you could skip the wrapper thing and directly implement the interface. I'm quite sure you don't have the source, though.