Suppose I want to inherit from System.Data.SqlClient.SqlTransaction which is sealed. Supose I want to just put a wrapper around SqlTransaction and always use MyTransaction instead of SqlTransaction. Is there a way I could potentially cast MyTransaction to SqlTransaction using an Implicit/Widening operator?
You could create a class that has an inner transaction variable and then expose the methods and properties. Kind of like this:
public class MyTransaction
{
System.Data.SqlTransaction myTx = someConnection.CreateTransaction();
public void CommitTransaction() : {
myTx.CommitTransaction()
}
}
You could also make it inherit from DbTransaction and then rewrite the abstract and virtual procedures to use the inner myTx variable, but it starts getting a little complex for no apparent real reason...
If you really want implicit conversion (although I would not recommend it, as it is a horrible idea and a horrible design, IMO), you can do something like this:
class MyTransaction
{
private readonly SqlTransaction _transaction;
public MyTransaction(SqlConnection conn)
{
_transaction = conn.BeginTransaction();
}
public SqlTransaction Transaction
{
get
{
return _transaction;
}
}
public static implicit operator SqlTransaction(MyTransaction t)
{
return t.Transaction;
}
}
If you are just interested in adding additional methods to a class you could use extension methods. That won't give you access to any internal state, or allow you to override behaviors, but it will let you add limited functionality. I'm not aware of any way to inherit from a sealed class.
You could create a true wrapper object as others have mentioned, but you won't be able to use it polymorphically in place of the original object.
OK, so ruling out the inheritance and focusing on the task you really want to solve (based on the comment threads).
I have had success in the past running all calls through a helper library and implementing the logic there. In the past, I have used SqlHelper, which is published in the Microsoft Data Application Block. This is a source module, which you can adapt to your needs. You can add whatever logging or other logic you require.
It also makes the code very readable. You can do things like:
SqlHelper.ExecuteDataset() for queries returning sets of data,
SqlHelper.ExecuteScalar() for queries returning single values,
SqlHelper.ExecuteNonQuery() for commands which have no returns (like INSERT's).
etc.
No, you cannot have your custom class be inherited from SqlTransaction or to have this faked.
However, if the context of what you are doing allows you to use a DbTransaction, you could inherit your custom transaction class from DbTransaction, wrapping up a SqlTransaction inside with whatever other functionality you require.
You do have another option, you could use Reflection.Emit() to add an interface of your choosing to SqlTransaction, and then use that same interface, in your new MyTransaction class and then you can make calls to the interface, instead of the class.
Take care that this will only work within libraries you create, or specifically modify the loaded types using Reflection.
You can create extension methods.
public static class SqlTransactionExtensions
{
public static void DoSomething(this SqlTransaction transaction, int myParameter)
{
// do something here
}
}
The class must be static. Place the magic word this in front of the fist parameter which must be of the type of the class you are extending. You can extend interfaces as well. If you want to use this extension method, then you must have a using namspace with the namespace of this extension class, if it is not defined in the same namespace you are working in.
You can then call the extension method as if it was a regular method of SqlTransaction:
SqlTransaction t = new SqlTransaction();
t.DoSomething(5);
You can define your own MyTransaction class as a wrapper around SqlTransaction. Keep an instance of SqlTransaction in a private field inside MyTransaction. Your wrapper will not be assignment compatible with SqlTransaction, but if you implement the same interfaces SqlTransaction implements you can get pretty close.
Related
From unit testing and dependency injection point of view, what's the usual adopted norm when it comes to helper methods?
Here is my example situation:
public class GoodiesController : Controller
{
private IMyContext _context;
public GoodiesController(IMyContext context)
{
_context = context
}
public async Task<IAction> GetThoseGoodies()
{
if(YouLikeThemThisWay(Request.Path))
{
var result = await _context.GoGetThemThisWay()
} else { }
}
My question is am I better off with YouLikeThemThisWay(string path) as a static helper in some class or as a private instance method? Assuming I might have a couple of the likes of YouLikeThemThisWay?
It really depends on what your YouLikeThemThisWay(string path) method does. My rules for using a static method or as follows:
Does it require a non-primitive dependency? If so, don't use static.
Does it affect the state of the application? If so, don't use static.
Does it extend the functionality of a class or type you do not have access to internally (IE BCL classes or primatives)? If so use a static extension!
Will it impact unit tests--as in make them more difficult--if I cannot mock the routine? If no, then make it static!
Will it be used by more than one type or class? If so that it makes it a better candidate for static!
Does the routine perform some sort of IO, like calling a database or the filesystem? If so, I would not make it static.
Basically, small helper functions that are easily tested and don't affect state or usually OK to make static. If there is state involved, the routine requires a dependency that you would normally inject, or the routine is making IO or IPC calls then do not make it static.
One caveat to the dependency issue is technically you could use method injection to handle the dependencies, but I like to keep it simple. Your method is probably OK to be static.
Reuse is a big factor in statics too. If the routine will only be used in one class, it may be pointless to make static. Most of my static methods live in helper classes that are easily accessed anywhere.
EDIT: Note that I usually require most or all of those five rules to favor statics in order for me to even consider making something static.
Sorry if the question sounds confusing. What I mean is that if I have a class that has a method that does a bunch of calculations and then returns a value, I can either make that method public (which gives my other classes access), or I can make it private and make a public get method.
Something like this:
public publicmethod{
return privatemethod();
}
private privatemethod{
//do stuff
return value;
}
Is this a futile exercise or does it provide additional program security?
Well, there is no additional security here. However, such a usage can sometimes make sense.
For example, the private and public method may have different semantics.
// base class
public virtual BuyFood()
{
BuyPizza();
BuyCoke();
}
private void BuyPizza()
{
// ...
}
// derived class
public override void BuyFood()
{
BuyChopSuey();
}
private void BuyChopSuey()
{
// ...
}
So your implementation is just calling to a private method -- but what is important, you expose the semantics: your BuyFood operation is just BuyChopSuey(). Your code says: "in this class, buying food is just buying chop suey" in a clear way. You are able to add BuyTsingtaoBeer() into BuyFood() any time without changing the semantics of the both methods.
It is completely redundant. It does not provide anything except another name for the same thing and another indirection for readers to follow. Simply make a single implementation, and make it public. On the same note, getX() { return x; } setX(T newX) { x = newX; } does not encapsulate anything, at best it's future-proofing.
You may end up implementing a particular function required by an interface in a single line, largely delegating to (possibly private) methods which exist for other good reasons. This is different, and more justified (but again, if it's only return someMethod(); you should probably abolish the private implementation and assume the common name). A particular case if when you need two implement two methods which do the same thing (e.g. from separate interfaces).
I think either way is fine, it's more a matter of style assuming the method doesn't change the state of the class. If you have a class that has a bunch of properties and very few methods, it probably makes more sense to define another property. If you have a lot of methods in the class but few properties, then a method is more consistent with your overall class design.
If the method changes a bunch of other class variables than I'd expose it as a public method instead of a property.
I don't think either way, property or method, is necessarily more secure. It depends on what checks you do - is the caller allowed to perform the calculation? Are all variables used in the calculations within acceptable ranges? Etc. All of these checks can be performed whether you are using a property or a method.
Well, actually the question is What code do I want to be able to call this method?
Any code in general, even from other assemblies? Make the method public.
Any code from the same assembly? Make it internal.
Only code from this class? Make it private.
Having a private method directly aliased to a public method only makes the private method callable from the outside, which contradicts its private status.
If the method only does some calculation and doesn't use or change anything in the object, make it a public static method:
public static CalculationMethod(int input) {
//do stuff
return value;
}
That way any code can use the method without having the create an instance of the class:
int result = ClassName.CalculationMethod(42);
Instead of public consider internal, which would give access only to code in the same assembly.
Let's say I have some classes defined as follows:
class Security
{
Boolean AuthenticateUser(String username, String password);
Boolean AddUser(String username, String password);
// many more methods
}
class NetworkedDevice
{
void Stop();
void Start();
// many more methods
}
Then I have another class that contains instances of the above classes. How can I avoid code like the following? I want all the methods of class1 and class2 exposed via this class.
class MyWindowsService
{
Security _security = new Security();
NetworkDevice _netDevice = new NetworkDevice();
Boolean AuthenticateUser(String username, String password)
{
return _security.AuthenticateUser(username, password);
}
// all the rest of "Security" methods implemented here
void StopNetworkDevice()
{
_netDevice.Stop();
}
void StartNetorkDevice()
{
_netDevice.Start();
}
// all the rest of "NetDevice" methods implemented here
}
Edit
I've updated the code to be more real to what I am doing. I am hosting a WCF service within a windows service. The windows service does several things including user authentication and communication to networked devices to name a few. The implementation of my WCF interface calls methods of the "MyWindowsService" class. Exposing the underlying objects as properties is the answer I was looking for. The above class then looks something like:
class MyWindowsService
{
SecurityClass _security = new SecurityClass();
NetworkDevice _netDevice = new NetworkDevice();
Public NetworkDevice NetDevice
{
get { return _netDevice; }
}
Public SecurityClass Security
{
get { return _security; }
}
}
Well, if you're using composition (as you are) there is no "easier way"; you just have to wrap the methods you want to expose. If you want to expose all of the methods of the composed type, then why are you using composition in the first place? You may as well just expose SecurityClass and NetworkDevice via public properties as it is functionally no different than wrapping every method and property/public field.
If it makes sense that they belong in the inheritance chain then SuperClass (oddly named as it would be a sub class...) should inherit from one of those classes. Of course you can't inherit from both in C#, but this design makes me suspect that there may be a better overall approach. It is impossible to tell from your code sample though as you don't tell us what you are actually trying to accomplish with these types.
There is one more way: T4 Templates.
See here: http://msdn.microsoft.com/en-us/data/gg558520
The resulting CS file is generated at build time. This means you could potentially loop your classes using refelection and the result would be what you have now manually created in your "SuperClass".
The cool thing really is that the resulting code is generated on the fly and it is typesafe.
Is it worth the effort? I don't know. It really depends what you are doing and why you are doing it.
We use it for instance to translate Func<T1, T2> into "real" delegates and auto-generate wrapper classes that way.
Unfortunately there is no magic ways to do that as multiple type inheritance is not allowed in .NET.
You cannot do this easily in C#. You could inherit from one of the classes, and create delegates for the other, or you can manually create delegates for both (by delegate, I just mean a method that delegates to the member object, not anything to do with the delegate keyword or class).
If you use a product such a Resharper, there is an option in the Refactor menu that will automate this process, called "Create delegates..."
You can make class1 public and then reference them directly:
SuperClass.class1.MethodFirst();
Of course, static methods will be ok, you will have to construct class1 for instance methods.
in C#, you cannot combine class hierarchies the way you can in Java but you can enforce a contract through iterfaces.
Create an interface for Class1 and Class2 then have SuperClass implement those interfaces. You'll still code up the method calls, but at least you'll have some compile-time checking in place. Perhaps you could also Create a method in SuperClass that dispatches to the appropriate class/method using reflection.
Another approach might be to setup an inheritance chain where SuperClass extends Class2 which extends Class1.
The question is rather old already, and there's one more solution available today: Expose.Fody. This is a plugin for Fody, which is a general-purpose IL-weaving tool. To quote the Expose's description,
Exposes members and optionally implements interface of a field declared in class.
All it takes is just decorating the field with an attribute.
I am using .NET 3.5 C#. I have a simple connection class with only two methods: OpenConnection() and CloseConnection(). I defined this class as Static so that I don't have to create an instance while calling methods. I want to know whether:
(1) I should create an interface with method definitions for OpenConnection and CloseConnection and thereby use this Interface with Connection class. There is no reason to use an interface but I was thinking whether the Connection can be made more professional.
(2) Is it fine to declare this class as Static?
There are two entirely different approaches
Singleton: Single object across the application.
In this case, you will have to take care of the locking mechanism as well.
class Connection
{
public static Connection Instance() {
if (_instance == null) {
lock (typeof(Connection)) {
if (_instance == null) {
_instance = new Connection();
}
}
}
return _instance;
}
protected Connection() {}
private static volatile Connection _instance = null;
}
Implement IDisposable:
Alternatively, you can implement IDisposable in your Connection class, and let it disposed automatically using the using keyword. For instance:
using(Connection c = new Connection(SomeConfiguration)) //Opens the connection.
{
Something(c);
}// Closes the connection. Dispose is implicitly called in the scope of the using statement.
Or if you want Generic Connection class, then Marc has responded with an excellent database connection class example here.
Regarding point 1; you can use interface; iff:
You want loose coupling, componentization, and maintainability in your code.
You want to provide guarantee that the classes shall behave exactly as methods/contracts defined in interface. For instance, in this case, if you extend your class from IDisposable, the interface imposes that not only objects can be disposed without getting compiler errors, but that they should be disposed. So, similar guarantees can be provided in your code by simply adhering to an interface.
You have a team that is going to working on a large module; and you want to keep code consistent; so you can define an interface and add some restrictions, that would help integrate the it easily. For instance:
You know you have a module that is going to handle alot of connections, different types of connections - some of which may be identified later during the development. But what you know for sure is that all types of connection shall be able to Open and Close; and you also want all of the developers to stick to this rule. So you can come up with an interface like:
interface IMyConnection
{
Open();//Opens the connection
Close();//Closes the connection
}
You expect have certain classes that does a lot of complex work and won't be finished before the rest of the project; then rest of the project can use the interface and avoid being dependent on that class.
You plan to deploy your product commercially; and want it to be extendable by 3rd party developers.
If you use interface, you cannot define Static method. (or in other word, static method is always pointing to the class defined, so the interface cannot provide abstraction at this point).
A class can be static, as long as you want everything shared, and extension to it is not necessary. But I would strongly recommend you to look at Singleton Pattern and Abstract Factory as alternative to your design problem.
interface IConnection {
void Connect();
void DisConnect();
}
class TCPCustomConnection : IConnection{
// implement other stuff
// Singleton Pattern
static IConnection Instance {
privateInstance = privateInstance ?? new TCPCustomConnection();
return privateInstance;
}
}
From what you said so far, I don't see how the interface adds value. If it does not add value, it should be eliminated from the design. The interface introduces two new problem: You need to get a pointer to the interface implementation, and usually you want to avoid asking for it repeatedly. So don't do it unless adds value (in a tangible, not metaphysical way) to your design.
An interface might add value if it simplifies unit testing of your code, or if it is important to remove the runtime dependency on the assembly that implements the connection. This is very fashionable these days.
simple a static class is requird, if it just used for demarcating operations like open and close connection, favor simplicity rather, dont code for future scenario until it is absolutely necessary and don't change existing working code till you reach a point where it is absolutely requirea
My advice:
(1) Why you need to write your own Connection class since it's "a simple connection"? None of the built-in classes meets your requirement?
(2) According to MS examples, it's really weird to make Open and Close methods static. We are used to this:
conn.Open();
conn.Close();
instead of:
MyConnection.Open(conn);
MyConnection.Close(conn);
(3) Using interfaces is a good idea, especially IDisposable:
class MyConnection : IDisposable
{
public void Dispose()
{
//close the connection and release resources
}
}
using (MyConnection conn = new MyConnection(connStr))
{
} //automatically Dispose()
If you have different connection type, like UDP, TCP, COM Port, ... using interface is good for manageability, but in the case which you have just one connection there is no need to use interface, also i think using static and singleton is not useful here, you should have a service for your tcp connection to always keep it up, and when you got disconnected you should be able to repair connection. for a good tcp server sample see http://fadd.codeplex.com/SourceControl/changeset/view/58859#1054893.
Even if you think that you'll only ever need one connection, I'd still use an instance class that implements an interface to handle it.
Why?
I can easily swap implementations if I need to (or refactor an existing one).
I can unit test things that depend on the class by mocking the connection.
I can more easily control the lifecycle of the connection (eg by using IDisposable).
Consumers of any API I write can see what my dependencies are.
If the single instance requirement does change, I don't have to unpick all the references to the static/singleton methods.
The testing point here is important: if you use a static reference to a fixed external resource, your code will be virtually impossible to unit test independently of that resource.
See this answer for a similar discussion about static versus instance classes and methods.
I'd like to override a class method without inheriting the base class because it'd take a lot of time and modifications and, therefore, more and more tests. It's like this:
class TestClass{
public void initialMethod(){
...
}
}
And somewhere on the code, I'd like to do something like this:
public testMethod()
{
return;
}
test(){
changeMethod(TestClass.initialMethod, testMethod);
}
And this changeMethod function would override the TestClass initialMethod so that it'd call testMethod instead.
Inheriting and overriding the method using normal practices is not an option, as this class A is a graphic component and, inhereting it (and changing it) would break lots of code.
Edit: We don't have the base code for the TestClass, so it's not an option to modify the code there defining the initialMethod as a delegate.
Edit 2: Since this is a graphical component, the designer added a lot of code automatically. If I were to inherit this code, I would have to replace all code added by the designer. That's why I wouldn't like to replace this component.
You need the Strategy pattern.
Main steps:
Create an interface with ie. Do() signature
Your initialMethod() should call a strategy.Do(), where strategy is type of your interface
Create a class that implements this interface. Do() is your testmethod now.
Inject into your main class an instance of this class
If the job it's not so big (let's say just a color replacement or something) then I agree with Jhonny D. Cano's solution with C# (anonymous)delegates.
Edit (after edit 2)
May - just as proof-of-concept - you should inherit the class and replace all references from base class to this new. Do this, and nothing else. If it works, you can think about the next steps (new methods or delegates etc.)
You need only a new checkout from your version control system, and if it maybe fails you can abandon it. It's worth trying.
Perhaps you can do it as a delegate.
class TestClass {
public Action myAction;
public void initialMethod(){
...
}
initialMethod
public TestClass() {
myAction = initialMethod;
}
}
and then on TestMethod
public testMethod()
{
return;
}
test() {
testClassInstance.myAction = testMethod;
}
I think your best bet might be to use a AOP framework like LinFu. There's a codeproject article explaining it:
Introducing LinFu, Part VI: LinFu.AOP – Pervasive Method Interception and Replacement for Sealed Types in Any .NET Language
If 'TestClass' is something you defined, you could replace the 'initialMethod' definition with a property and delegate which can then be set to any method with a given signature. (Even anonymous ones.)
class TestClass {
Action _myMethod;
Action MyMethod {
get { return _myMethod; }
set { _myMethod = value; }
}
var tc = new TestClass()
tc.MyMethod = () -> Console.WriteLine("Hello World!");
tc.MyMethod()
The above code is untested.
The short and simple answer is: if you can't adjust the base TestClass code, no, there's no way you can modify the class to replace a method by another. Once we started doing stuff like that, we'd be in a completely different kind of language, like JavaScript.
The longer answer is: it depends on who is calling the replaced method.
If it's other classes, see if you can't implement a Proxy in between them and the unmodifiable concrete class. Whether this is doable depends on whether that class implements interfaces, or is its own interface.
If it's the class itself, then your only option is to decompile and modify the class, at design time using Reflector (or equivalent tools), or at runtime using Reflection.Emit. However, you'd have to be hurting pretty badly to go this route, as it's sure to be painful and brittle.
Unfortunately you still haven't explained what you are trying do and why. Replacing methods on the go is powerful stuff in the languages that permit it directly... There might be mocking libraries that can be twisted sufficiently far to do the reflection stuff, but then you'd be skating on thin ice.
If you don't have the code use Extension Methods.
public void doSmth(this objectYOUWANT arg)
{
//Do Something
}
Here you use the principle Closed for Modification Open for Extension.
This will add functionality to the library you don't have the source code. It's very clean to do it this way.
Edition:
In FrameWork 3.5 there is something new called Extension Methods. These kind of methods adds functionality to a closed Assembly letting you Extend in functionality a closed dll/assembly.
To use this for example you have a dll that you import, that is called Graphics.dll (you have the reference on your project)
First of all you shoud create a new static class called for example Extension:
public static class Extensions
{
}
Second, you want to add extra functionality to a class contained in Graphics.dll named ChartGraph. You will do this:
public static class Extensions
{
public static void draw(this ChartGraph g)
{
// DO SOMETHING
}
}
Third, when you instantiate a new object from the graphics.dll you now will have the new method you have created:
ChartGraph myG = new ChartGraph();
myG.draw();
As you can see there you have added new functionality without much effort without recompiling the dll, this is good if you don't have the source code.