I am building a site using entity framework 4.1 and mvc3. I am using the Generic Repository pattern:
http://www.tugberkugurlu.com/archive/generic-repository-pattern-entity-framework-asp-net-mvc-and-unit-testing-triangle. I use ninject to inject my concretes repositories to the controllers.
My problem is that each of my dbcontext different and I cannot run complex queries without the code shouting something like "different contexts cannot be used in the same query". I tried using the "singleton" approach but then code shouted something like "tried to enter a disposed object (null reference exception)".
Does anyone have an idea of what I'm doing wrong?
The Singleton pattern is an anti-pattern that should be avoided. It leads to hard to test code with all kinds of side effects (for example, a disposed DbContext).
The UnitOfWork manages operations on different repositories. It will keep track of all the changes that are made and then it will write those changes in the right order to your database. The DbContext already implements the UnitOfWork pattern (Altough it's nicer to hide the DbContext behind a custom UnitOfWork interface).
If you are already using dependency injection trough NInject you are almost their! You should change the constructors of your Repository to take a DbContext:
public class MyRepository
{
private _unitOfWork;
public MyRepository(DbContext unitOfWork)
{
_unitOfWork = unitOfWork;
}
....
}
If you then wire the DbContext to NInject with a InRequestScope mode everything should work. Your DbContext will then be shared by all Repositories and Ninject will dispose of it at the end of your request.
Not sure if I'm getting your question or not, but your repositories should be able to work within a "Unit of Work" which would have a single dbcontext.
I find the best place to start this unit of work is on the begin request, which you can setup in your global.asax ( and the end request for tear down )
Related
I have a web application that uses linq-to-sql queries (will soon be upgraded to linq-to-EF compiled queries) and for which there's data context and a database already in place. I want to create a demo version of the application and for the demo, I want to use an entirely different database file but that will have the same tables. So in essence, I'll have the same data structure for two different databases: one database for logged-in users and one database for demo users. I want to reuse many of the queries I've already written; they look like this:
public class FruitQueries
{
public List<SomeObjectModel> MyQuery(list of parameters)
{
using (MyDataContext TheDC = new MyDataContext())
{
var TheQueryResult = (from f in TheDC.Fruits
......).ToList();
return TheQueryResult;
}
}
public List<SomeObject> AnotherQuery(some other parameters) {...}
}
Now I think I know that this calls for dependency injection where the data context is passed in as a parameter but I'm not sure on the syntax. How do you reuse queries using dependency injection to make them work on two different databases? Right now I'm using a using statement and I want to keep this pattern; is that possible if I inject the DC as a parameter?
Thanks.
Since you already have a lot of code in place, probably the simplest thing to do is to inject a factory:
public interface IMyDataContextFactory
{
MyDataContext CreateNewContext();
}
All the code will roughly stay the same:
public List<SomeObjectModel> MyQuery(params)
{
using (var TheDC = this.factory.CreateNewContext())
{
var TheQueryResult = (from f in TheDC.Fruits
......).ToList();
return TheQueryResult;
}
}
You can let the injected IMyDataContextFactory decide how to construct a MyDataContext instance (based on the user). This would be trivial.
In the end it will probably be better to inject a MyDataContext (or an abstraction such as IUnitOfWork) into consumers, but this changes everything completely. Since this class is passed in from the outside, the consumer isn't responsible anymore for disposing it, but someone else is. Although disposing such instance isn't that hard with most DI container. It gets harder though when you want to share the same MyDataContext instance over multiple consumers (within the same web request for instance) and where do you call SubmitChanges?
Elaborating the previous answer
What you can do, is provide the connectionstring to the DC (would this qualify as contructor injection?)
using (MyDataContext TheDC = new MyDataContext(this.factory.CreateConString()))
This way, disposal is still handled by the consumer and you can continue your Using() approach. Your factory can read the two different connectionstrings from your webconfig and determine the right one to use, based on the user. (not that trivial as it may seem)
PS: I think the quickest way is to deploy the demo application to a different URL so they can have a separate web.config and you do not need to code anything but that does not answer your question.
I have build my site using entity and repository pattern with ninject injection. My problem is my connections don't seem to get disposed. I have around 30 repositories (one for each table) and I get sql expiration timout preety quick. I can't use the regular using statement because the code recognize only the interface before the injection.
(in each controler I have my repositories interface instances which get injected via ninject).
I have searched the net but couldn't find a solution that was accurate for me.
can anyone please help me?
code example:
this is in the ninject controller under addBindings():
ninjectKernel.Bind<IMovieRepository>().To<MovieRepository>().InRequestScope();
and one of my repositories:
public class MovieRepository : IMovieRepository, IDisposable
{
private Entities dataContext = new Entities();
public System.Data.Entity.DbContext DbContext
{
get { return dataContext ?? (dataContext = new Entities()); }
}
public void Dispose() { dataContext.Dispose(); }
}
and in the Global.asax file:
ControllerBuilder.Current.SetControllerFactory(new NinjectControllerFactory() as IControllerFactory);
I would guess that your repositories (and therefore presumably your DbContexts) are being bound in transient scope, which I believe means a new one will be created every time Ninject needs to inject one somewhere. I'm not certain but I'm guessing then that these are all staying around for the lifetime of your application and maybe not being disposed.
Try binding your repositories in request scope, so that they are created and disposed per web request.
e.g.
Bind<IFooRepository>().To<ConcreteFooRepository>().InRequestScope();
From the Ninject wiki:
There are four built-in scopes available in Ninject:
Transient - A new instance of the type will be created each time one is requested. (This is the default scope). Binding method is .InTransientScope()
Singleton - Only a single instance of the type will be created, and the same instance will be returned for each subsequent request. Binding method is .InSingletonScope()
Thread - One instance of the type will be created per thread. Binding method is .InThreadScope()
Request - One instance of the type will be created per web request, and will be destroyed when the request ends. Binding method is .InRequestScope()
This kind of problem usually occur if long living objects depend on shorter living objects. E.g. A singleton service uses a repository in request scope.
I have created the following classes for sharing images. They implement an interface, but I need a way of switching between them with user interaction. I've done it the following way:
As you can see, service 1 and service 2 implement iSharingServices, and inherit from PolimorphSharing.
PolimorphSharing is simply and an abstract class that implements the methods I want public from Service 1 and Service 2. Those methods will then be overridden on the Service 1 and Service 2.
Because I need a way to switch the service in runtime, I've created a gateway class that inherits from PolimorphSharing. I can then call it the following way:
private var sharingService:PolimorphSharing = new SharingServicesGW('svc1').createService();
This all works flawlessly, and I can now switch between services with no problem whatsoever. However, I feel there's something wrong about it, so I would like to ask you guys for some advice on how to better implement this.
Any opinions here would be appreciated. I feel like I'm kind of implementing the factory pattern here the hard way.
UPDATE:
Just adding some more insight to this. Basically the idea here is for my client to be able to upload images with various different public sharing services such as imageshack, imgur etc. I want my client to be able to select the service in which the image is to be published to (hence the "switching between them with user interaction" bit of the question.
The method that does the uploading bit, is requestShareImage(), processResults() simply turns whatever gets returned to a unique format, so my client can read off it always the same way. getObject() is my accessor, and onIOError will handle exceptions with any of the public API's
Thanks all in advance,
SharingServicesGW IS a factory. However, there's no need for it to - and it shouldn't - inherit from PolimorphSharing. Also you're doing it a bit skewed. The client should be using objects of the interface type, not the abstract type.
Your interface should be defining the public API, not your abstract base class. In fact in AS3 interfaces can only define public members, while pseudo abstract classes can enforce implementation of protected members.
-- EDIT --
here's a UML diagram of how I would do it
I've got a bit of a problem. I'm working in the Castle Windsor IOC Container. Now what i wanted to do is just mess about with some AOP principles and what i specifically want to do is based on a method name perform some logging. I have been looking at Interceptors and at the moment i am using the IInterceptor interface implemented as a class to perform this logging using aspects. The issue is if i want to perform the logging on a specific method then it gets messy as i need to put in some logic into my implemented aspect to check the method name etc...
I have read that you can do all of this using Dynamic Proxies and the IInterceptorSelector interface and the IProxyGenerationHook interface. I have seen a few examples of this done on the net but i am quite confused how this all fits into the Windsor container. I mean i am using the windsor container which in my code is actually a ref to the IWindsorContainer interface to create all my objects. All my configuration is done in code rather than XML.
Firstly does anyone know of a way to perform method specific AOP in the windsor container besides the way i am currently doing it.
Secondly how do i use the Dynamic Proxy in the windsor container ?
Below i have added the code where i am creating my proxy and registering my class with
the interceptors
ProxyGenerator _generator = new ProxyGenerator(new PersistentProxyBuilder());
IInterceptorSelector _selector = new CheckLoggingSelector();
var loggingAspect = new LoggingAspect();
var options = new ProxyGenerationOptions(new LoggingProxyGenerationHook())
{ Selector = _selector };
var proxy = _generator.CreateClassProxy(typeof(TestClass), options, loggingAspect);
TestClass testProxy = proxy as TestClass;
windsorContainer.Register(
Component.For<LoggingAspect>(),
Component.For<CheckLoggingAspect>(),
Component.For<ExceptionCatchAspect>(),
Component.For<ITestClass>()
.ImplementedBy<TestClass>()
.Named("ATestClass")
.Parameters(Parameter.ForKey("Name").Eq("Testing"))
.Proxy.MixIns(testProxy));
The Test Class is below:
public class TestClass : ITestClass
{
public TestClass()
{
}
public string Name
{
get;
set;
}
public void Checkin()
{
Name = "Checked In";
}
}
as for the interceptors they are very simple and just enter a method if the name starts with Check.
Now when i resolve my TestClass from the container i get an error.
{"This is a DynamicProxy2 error: Mixin type TestClassProxy implements IProxyTargetAccessor which is a DynamicProxy infrastructure interface and you should never implement it yourself. Are you trying to mix in an existing proxy?"}
I know i'm using the proxy in the wrong way but as i haven't seen any concrete example in how to use a proxy with the windsor container it's kind of confusing.
I mean if i want to use the LoggingProxyGenerationHook which just tell the interceptors to first for methods that start with the word "check" then is this the correct way to do it or am i completely on the wrong path. I just went down the proxy way as it seems very powerfull and i would like to understand how to use these proxies for future programming efforts.
By using .Interceptors() you already are using Dynamic Proxy. When component has specified interceptors Windsor will create proxy for it, and use these interceptors for it. You can also use method .SelectedWith and .Proxy property to set other options you already know from DynamicProxy.
I just added a website about Windsor AOP to documentation wiki. There's not much there yet, but I (and Mauricio ;) ) will put there all the information you need. Take a look, and let us know if everything is clear, and if something is missing.
In a multilayer application (ASP MVC: UI project, DAL project) i registered in web.config the components.
Now i have this problem: Unit of Work pattern has do be implemented and i need to get the current instance of a particular service. The registration of the services happened in the UI project, but i need to get the current instance of this service in the DAL project. How do i get this reference?
In the UI project i already needed a way to get something resolved:
container = new WindsorContainer(
new XmlInterpreter(new ConfigResource("castle"))
);
personRepository= container.Resolve<IPersonRepository>();
Would it be OK to use the same technique in the DAL project? If yes, should i write the configuration in a separate file, so that it can be accessed by all the layers(projects)?
Sorry for this (i think) naive question but it's my first project using Castle and i think i don't understand the big picture of it!
Code snippet would help a lot.
Thanks in advance!
In a nutshell: one container instance per application, one container configuration that has all the components you need for the application. If you need a service in your DAL, inject the appropriate service interface in your DAL class via constructor (if the dependency is required) or setter (if the dependency is optional).
Try really hard to avoid using a static IoC gateway, it hides the true dependencies of a component and it hampers testability.
See these related questions:
Usage of IoC Containers; specifically Windsor
Is it correct to have many Castle Windsor containers per application if those containers belong to different tiers?
Have a look at this article. It shows you how to write a static class that performs dependency resolution using Castle Windsor. You should consider putting this class in a separate project that can be referenced from both your UI and DAL projects to allow code reuse. As the article explains, your class should provide a bootstrapper facility that initializes your IoC container. In your case, this would look like:
public static class IoC
{
private WindsorContainer _container;
public static void Initialize()
{
_container = new WindsorContainer(
new XmlInterpreter(new ConfigResource("castle"))
);
}
}
The bootstrapper would be invoked from the application startup event in your UI projects Global.asax file.
The other methods for obtaining instances of objects from the container would be as per the article.