I have some business logic in stateless EJB, but the logic is too complex and too big for one EJB. So I can see the following things to do here:
1) Extract the logic into some helper classes and instantiate them in EJB, so EJB will be like a facade for all the business logic.
Disadvantages that will be here: EJB has a lot of injected resources (e.g. queues, connectionFactory, other EJB's), so I have to pass those in a constructor to helper classes. Maybe not that convenient, but doable.
2). Create more local stateless EJBs with business logic and inject.
Disadvantages that will be here: I'm not sure if having a lot of local EJB's actually affects the performance of the whole application. Probably somehow it does: it has to add it to pool, instantiate etc.
I'm using EJB3.0 and WebLogic as a container.
What would u say will be a better approach?
Thanks
Related
I'm seriously start thinking that usage of IoC container provokes to create overdesigned solutions (at least it provokes me to try to use various unnecessary features:).
It's the time to synchronize my "IoC" antipatterns list with community one's..
My short experience tell that it is absolutely enough to call Resolve method once per application at startup to resolve some infrastructure singletons and initiate with them "transient object's factory" that could produce new "smaller life time grain factories" . Even to make those factories thread safe (e.g. create one instance per thread) is so easy to achieve by adding 10 code lines into factory... Still those factories are much more simpler then "library's integration with IoC tool". Interception? Just create your own wrappers... Life time managers / dependency strategies/ parent containers? Call the Resolve only once at bootstrapper and you won't think about that.
Could you help me to understand why developers call Resolve several times on different application layers (by passing container or by passing delegate to container) and then have a lot of things to think about? I really worry that I miss something.
Some kind of IoC are anti-patterns or may be in some cases. For example the service locator antipattern. But if you are using constructor injection at the beginning of your application - and only there - then it should not lead to an anti-pattern.
Injecting a DI container interface in a class is a wrong use of constructor injection. If DI is not part of the business logic of your class it should not know or depend on DI container nor should it depend on IKitchen. It's only fine to inject your DI container in some kind of helper or service working in conjunction with your dependency injection container, because it's purpose is to work with or around DI container. The examples in the links you give are misuse of IoC. It does not mean that IoC in general is an anti-pattern.
I think the correct question would be "Can constructor injection be an anti-pattern?". So far I've never faced any situation or seen any example where it was so I would say "no", until I face such a situation.
When it was not clear to me how to use an IoC container, I decided to stop using it, because I thought was just an overcomplication over the simple dependency injection.
It is true though that even without IoC is possible to fall in the over-injection cases.
A while ago I read some posts from the author of ninject that opened my mind.
As you already know the injector should be used only inside the context root. However, in order to avoid over-injections, I decided to introduce an exception of the rule for injected factories.
In my framework, factories (and only factories) can use the injector container. Factories are binded in the container in the context root and therefore can be injected. Factories become valid dependencies and are used to create new objects inside other objects, using the injector container to facilitate dependencies injection.
Read This
Clearly something wrong. New library should not bring additional complex code.
I've found somebody who possibly could understand me :)
Constructor over-injection anti-pattern
Other antipattern in my eyes is pushing the initialization of container "deeper" then actual bootsrapper.
For example Unity and WCF recommendations
Bootstrapper in wcf app is the service constructor, then just put container initialization to constructor. I do not understand reasons to recommend to go for programming wcf sevice behaiviors and custome sevice host factory: if you want to have "IoC container free" bootstrapper - it is absurd, if you need to have "IoC container free" service contract implementation - just create second "IoC container free" service contract implementation.
In an n-tier architecture, the best place to put an object-relational mapping (OR/M) code is in the data access layer. For example, database queries and updates can be delegated to a tool like NHibernate.
Yet, I'd like to keep all references to NHibernate within the data access layer and abstract dependencies away from the layers below or above it. That way, I can swap or plug in another OR/M tool (e.g. Entity Framework) or some approach (e.g. plain vanilla stored procedure calls, mock objects) without causing compile-time errors or a major overhaul of the entire application. Testability is an added bonus.
Could someone please suggest a wrapper (i.e. an interface or base class) or approach that would keep OR/M loosely coupled and contained in 1 layer? Or point me to resources that would help?
Thanks.
It sounds like you are looking for the repository pattern. If you need more decoupling, you can inject the data dependencies with an Inversion of Control container.
Service Facade Pattern is one name. Simple contracts between business logic and data layer.
Service classes or beans (call it what you want) define and implement the contract, and orchestrate the lower data layer, often handling the transactional logic across data objects.
In Spring, you define an Interface, and then implement it. One implementation might be an OR/M, another might be raw JDBC or ADO.NET. In some frameworks, Aspect Oriented Programming allows you to inject declarative transactional logic without writing any code. It saves a lot of headache.
One caveat: When dealing with some OR/Ms like Hibernate, there is the use of proxy classes. This does pollute things, because there are a few instances where the proxy classes cause problems. In my opinion, that is an implemtation detail that should not escape the service layer. But with Hibernate, it does. Not sure about the .NET implementation.
I'm trying to get to grips with NHibernate, Fluent NHibernate and Spring.
Following domain-driven design principals, I'm writing a standard tiered web application composed of:
a presentation tier (ASP.Net)
a business tier, comprising:
an application tier (basically a set of methods made visible to UI tier)
repository interfaces and domain components (used by the application tier)
A persistence tier (basically the implementation of the repository interfaces defined in the business tier)
I would like help determining a way of instantiating an NHibernate ISession in such a way that it can be shared by multiple repositories over the lifetime of a single request to the business tier. Specifically, I would like to:
allow the ISession instance and any transaction to be controlled outwith the repository implementation (perhaps by some aspect of the IOC framework, an interceptor?)
allow the ISession instance to be available to the repositories in a test-friendly manner (perhaps via injection or trough some shared 'context' abstraction)
avoid any unnecessary transactions being created (i.e. when only read-only operations have been executed)
allow me to write tests that use SQLLite
allow me to use Fluent NHibernate
allow the repository implementation to remain ignorant of the host environment. I don't yet know if the businese tier will run in-process with the presentation tier or will be hosted separately under WCF (in IIS), so I don't want to bind my code too closely to a HTTP context (for example).
My first attempt to solve this problem had been using the Registry pattern; storing the ISession instance in a ThreadStatic property. However, subsequent reading has suggested that isn't the best solution (as ASP.Net can switch the thread within the page lifecycle, I believe).
Any thoughts, part solutions, pattern names, pointers to up-to-date samples (NHibernate 2) will be most gratefully received.
I have not used Spring.NET so I can't comment on that. However, the rest sounds remarkably (or perhaps not so remarkably; we're hardly the first to implement these things ;) similar to my own experience. I too had trouble finding a One True Best Practice so I just read as much as I could and came up with my own interpretation.
In my situation I wanted transaction/session management to be external to the repository as well as keep repository concerns from bubbling up out of them (i.e. the code using the repository should not need to know that it's using NHibernate internally and shouldn't need to know anything about NHibernate session management). In my case it was decided that transactions would be created by default lest developers forget them, so I had to have a read-only escape mechanism. I went with the Unit of Work pattern with the NHibernate ISession instance store inside. Calling code (I also created a DSL interface for the UoW) might look something like:
using (var uow = UoW.Start().ReadOnly().WithHttpContext()
.InNewScope().WithScopeContext(ScopeContextProvider.For<CRMModel>())
{
// Repository access
}
In practice, that could be as short as UoW.Start() depending on how much context is already available. The HttpContext part refers to the storage location for the UoW which is, unsurprisingly, the HttpContext in this case. As you mentioned, for a ASP .NET application, HttpContext is the safest place to store things. ScopeContextProvider basically makes sure the right data context is provided for the UoW (ISession instance to the appropriate database/server, other settings). The "ScopeContext" concept also makes it easy to insert a "test" scope context.
Going this route makes the repositories explicitly dependent on the UoW interface. Actually, you might be able to abstract it some but I'm not sure I see the benefit. What I mean is, each repository method retrieves the current UoW instance and then pulls out the ISession object (or simply a SqlConnection for those methods that don't use NHibernate) to run the NHibernate query/operation. This works for me though because it also seems like the ideal time to make sure that the current UoW is not read-only for methods that might need to run CRUD.
Overall, I think this is one approach that solves all your points:
Allows session management to be external to the repository
ISession context can be mocked or pointed at a context provider for a test environment
Avoids unnecessary transactions (well, you'd have to invert what I did and have a .Transactional() call or something)
I can't see why you couldn't test with SQLite since that's more of an NHibernate concern
I use Fluent NHibernate myself
Allows the repository to be ignorant of the host environment (that is, the repository caller controls the UoW storage context)
As for the UoW implementation, I'm partially kicking myself for not looking around more before I started. There's a project called machine.uow which I understand is fairly popular and works well with NHibernate. I haven't played with it much so I can't say if it solves all my requirements as neatly as the one I wrote myself, but it might have saved development time as well.
Perhaps we'll get some comments as to where I went wrong or how to improve things, but I hope this is at least helpful in some way.
For reference, the software stack I'm using is:
ASP.NET MVC
Fluent NHibernate on top of NHibernate
Ninject for dependency injection
What you are describing is supported by the Spring.NET framework almost out of the box. Only for FluentNHibernate you need to add a custom SessionFactory (not a lot of code, look here:Using Fluent NHibernate in Spring.NET) to Spring.NET.
Every repository can use the same ISession, just inject the SessionFactory in your repositories and use Spring.NET's transaction services.
Just try it out, they have pretty thorough documentation imho.
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I'm trying to decide whether or not it makes sense to go through the extra effort to encapsulate my IoC container. Experience tells me that I should put a layer of encapsulation between my apps and any third-party component. I just don't know if this is bordering on overkill.
I can think of situations where I might want to switch containers. For instance, my current container ceases to be maintained, or a different container is proven to be more light-weight/performant and better fits my needs. If this happens, then I'll potentially have a lot of re-wiring to do.
To be clear, I'm considering encapsulation of the registration and resolution of types. I think it's a no-brainer to encapsulate resolution - I'd hope it's common practice to have a helper/util class delegating to the container.
EDIT:
The assumption is that I prefer to wire-up my types programmatically for type-safety, compile-time checking and refactorability. It's this code and its dependency on the container that I'm looking to protect myself from.
I've also been using an IoC container for several other projects that share a lot of the same relationships, but the container is a pain to work with so I want change. But, a change means I lose the reusability of the registration code. Hence, why I'm contemplating encapsulation. It's not a huge burden, but one that I'd, nevertheless, like to mitigate.
I'm looking to:
Minimize the impact of change in containers / versions of containers
Provide some level of type-registration consistency across projects that may use different containers
Provide interface methods that make sense to me (RegisterSingleton<T,T> rather than RegisterType<T,T>( SomeLifetimeProvider ) - using Unity as an example).
Augment the container as conditions/scalability requirements change e.g. adding better caching, logging, etc during resolution/registration.
Provide my own model for registering type mappings.
Say I want to create a bunch of RegistrationHandler objects in an assembly/package and so I can easily segregate registration responsibilities across multiple classes and automatically pickup these handlers without changing code anywhere else.
I realize this is a bit subjective, so pros/cons might be helpful
Thanks!
Do it later, and only if you actually have the need to change IOC containers.
Pick an IOC container that is non-invasive. That is, one where the objects being connected to each other don't have any dependencies on the IOC container. In this case, there's nothing to encapsulate.
If you have to pick an IOC container that requires that you have dependencies on the container, choose one with the simplest dependencies/API you can. If you need to replace this IOC container (and you probably won't), implement adapters that bridge the new API to the old one.
In other words, let the first IOC container be the one that defines the interfaces for any future container so that you don't have to invent your own, and you can delay any of this sort of work until you absolutely need it.
EDIT:
I don't see a way of guaranteeing type-safety short of either:
Designing a relatively complex implementation of the Builder pattern along with visitor implementations that would write IOC configuration files, or something equivalent.
Implementing a type-safe IOC configuration DSL. (My choice if I had multiple apps that required swappable IOC containers.)
Yeah go for it. It's not a whole lot of extra effort and like you say, it gives you better isolation from third party components.
It also means that you can easily switch out the IoC container if you find something that's better. I recently did this with swapping out the Spring.net IoC container for structuremap.
The ASP.NET MVC Contrib project on codeplex is a pretty good place to start. This is what I based my implementation off.
It's best practice to do something only if there's an actual need for it, and never code something that you guess to be required sometimes in the future (that's the so-called YAGNI-principle). If your architecture is ok, you can easily change the container, if it actually should become necessary...
If you think you need this kind of flexibility, you may look at the Common Service Locator project at CodePlex. It does exactly what you look for: providing a common facade for various IoC containers.
HTH!
Rather than encapsulating the IOC container itself, I prefer to isolate the locus of interaction with the IOC container. For example, in ASP.Net MVC, I generally limit the exposure to the container to the controller factory and the global.aspx.cs file, where it's usually setup.
In my mind, having a lot of code that knows about the IOC container is an antipattern that increases complexity. I've seen a fair amount of code in which objects feel free to ask the IOC container for their dependencies, and then they've basically reduced the IOC container to a high-maintenance Service Locator.
Since IOC containers can resolve dependencies to an arbitrary degree of depth, it's pretty easy to make the controller factory the component that's responsible for involving the inversion of control containers. The constructor for each controller essentially specifies the services/repositories/gateways it needs.
For any of my apps, swapping the IOC container would essentially be a matter of rewriting the code the configures the container (specifies the bindings, etc.) and hooks up the controller factory. For apps exposed as services, the same basic idea should be reasonably manageable, though depending on the constraints of your runtime, you might have to use setter injection rather than constructor injection.
I am developing a WCF web service which has become quite bloated. What techniques do you use to split up the implementation of the contract?
Well you have a couple choices:
First, you could leave it all in one class, but split up into different files using the partial class feature of C#.
Second, you could have the main service class just pass requests off to one of a number of other actual classes that are organized logically.
A third alternative is to consider refactoring to reduce the number of operations you have. Is there actually a use to all of the methods you're exposing?
Finally, you could always split up the service into multiple WCF services.
It's hard to answer your question if you don't give any more information.
Do you mean that your service interface is bloated, or the class implementation? It's hard to answer well, if I don't see the code, or have no other information, anyway, I'll try:
Notice that WCF service is basically just a regular class that implements an interface and has some attributes on its methods. So all the other good OO design rules apply to it. Think about what it does, does it have really single responsibility, if not try to outsource some of that responsibility to other classes that your service depends on. If you need a non-default constructor, use IInstanceProvider to create the service class, and supply it with its dependencies (or if you use Windsor Container use WCF Facility).
If you really want to you can streach your inheritance chain, and move some of the code to a base class. I don't do it, however and always prefer to use composition over inheritance.
Inspect your service contract, and think about how cohesive it really is. Maybe what you should do is to split it, into few smaller, more cohesive services.