I am working on a very large game project in Symfony, and keep running into variations of the same problem.
I have a service that I need to separate into multiple "sub-services" because there is too much code to be contained within one class. For instance, a custom JSON serializer handler that needs a separate handler service for each method of serialization.
I'm having trouble working out the best practice for passing dependencies between "families of services." I would preferably like to keep all the definitions within services.yml just so things don't break in the future, but am assuming that may not be achievable.
Here's a better example - I have an "ActionQueueService" which takes a rather lengthy queue of actions from the user. What I would like to do is create a separate class to handle each type of action, so -
ActionQueueService // processes action queue JSON and delegates to sub-services
AbstractAction
PurchaseAction extends AbstractAction
SellAction extends AbstractAction
HarvestAction extends AbstractAction
Now if these three "actions" are defined as services they can have their own dependencies. However, they all have to be injected into the ActionQueueService - what happens if there are 38 of them (which there will be one day).
The next logical step for me was to create ActionFactory. Now I'm only passing in one dependency to ActionQueueService, and it can invoke any action service simply by calling -
$this->actionFactory->get('Harvest');
The problem I have is that each child has it's own separate list of dependencies. A Purchase or Sell action would need the Character service and the ShopStock service, a HarvestAction would need the HarvestService. Because I've decided to use a Factory method, I have to instantiate the sub-service within the factory class. I don't want to pass every dependency into the Factory only to have that either a) inject every dependency into every child or b) handle some crazy child constructor logic.
One solution would be to pass the service container into the factory and come up with a naming convention that allows me to create the service on the fly. I've heard that this is fairly bad practice though. Maybe a wrapper around the service container that limits the amount of bad stuff that could be done with it.
If anybody has any ideas on how this could be solved with Symfony I'd appreciate it. There are similar answers out there but unfortunately I don't know any languages other than PHP/Symfony.
Related
I want to set up several ui elements based on system information at the time of the application start up (i.e. this is info not known a priori so to set it statically in the css or the fxml file).
Is the controller constructor the best place to do this?
A first consideration was to do that either on the start() or init() methods of the main class that extends Application but it seems the set up is rather preventing programmer from easily accessing ui elements all the way down the node hierarchy. (which on the other hand is extremely easy in the respective controller through the #FXML injection)
It depends on the kind of work you need done. If you need anything that relies on your application's stage, then perform it in the start method. If not, then it can be performed in the constructor, init, or start methods. Bear in mind that the launching mechanism expects Application subclasses to provide a no-arg constructor, so if you incorporate startup logic there, then avoid requiring constructor parameters.
However, if you're going to use a controller (which I would recommend), then this logic should occur in its initialize method, not in your application class.
If you need a reference to the stage from the controller, then you can find many such solutions to passing the reference to the controller here on SO, such as making the stage reference public and static in your application class, or having such a field in your controller that can be set from your application's start method.
I've got to the point with Symfony 2 / Doctrine 2 where I've come to realise that we have build too much business logic in our application into services & controllers - and not enough into the model.
We wish to introduce configuration to our models (to modify behaviour) potentially giving models access to services directly in order to carry out their behaviours.
I've noticed that the following question has the completely wrong answer marked as correct with 8 upvotes - so I know the approach we have taken up to now (anaemic model) is considered the 'correct' way to do things by a lot of Symfony 2 users. After reading more into domain driven design I know this is not the case.
Symfony2 MVC: where does my code belong?
I see a lot of bundles define the behaviour in the model and extend this in entities/documents. This pattern works to a certain extent - but I think we need to introduce an additional stage. Some of the behaviour of our models is optional and having that behaviour will depend on what additional bundles are registered in our application (so including X bundle will allow the application to do more things). An Example.
We have an order object which at the moment has a bidirectional relationship with entities in the courier bundle meaning there is a hard dependency. I want to decouple this and have the courier bundle(s) optionally add behaviour to the order. Consider this method call.
// no courier bundle is registered
$order->getShippingMethods();
// throws NoAvailableShippingMethodsException;
// one bundle registered
$order-getShippingMethods();
// returns an array with one shipping method
etc....
Now currently we have an OrderProvider service which just sits on top of the Entity Manager - so if you call
$orderProvider->GetOrder($id);
You just get the entity returned 'direct' from the database. My question here is what pattens are other people using here? I'm thinking about moving all 'business logic' into a model class that the entity extends, having the service layer pull the entity out (entity being dumb record with properties in the database and getters), and then configure the model using configuration (the configuration being injected into the OrderProvider service), which will modify the behaviour of the model. For the example given I might do something like (within the OrderProvider)..
// trimmed down for example purposes by removing exceptions etc.
public function getOrder($id)
{
$order = $this->orderRepository->findOneById($id);
if ($this->couriers){
$order->addCouriers($couriers);
}
return $order;
}
// this function would be called by the courier bundle automatically using semantic configuration / tags / setter injection
public function addCourier(CourierInterface $courier)
{
$this->couriers[] = $courier;
}
The other option that I have is to create a new type of object - which decorates the base order and is already configured (as it ITSELF will be defined as a service in the DIC) and inject the order into that. The difference is subtle and both approaches would work but I'm wondering which is the best path.
Finally I have one issue with all of this that I can't get my head around. If my base Order entity has relationships with other entities and THOSE entities need to be configured - where should this happen? For example if I access my customer thus.
$order->getCustomer();
I get the customer (entity). But It may be the case that I need to add some configuration to the customer object too - like
$customer->getContactMethods();
Now the behaviour of this method might differ depending on whether my application has registered a twitter bundle or a facebook bundle or something else. Given the above example I'm not going to get a sufficiently configured customer - but rather the 'vanilla' base entity. Only way I can see around this is to cut relationships between entities which require configuration and pull the entity from a CustomerProvider service:
$customerProvider->getCustomerByOrder($order);
This seems to me to be removing information from the model layer and moves back towards a reliance on using multiple services for simple tasks (which I'm trying to get away from). Thoughts and links to resources appreciated.
Edit: Relevant - I see the cons listed in the first answer every single day which is why I've asked this question -> Anemic Domain Model: Pros/Cons
It seems like a complexity of your project is the modularity requirement - application behavior must be extensible via bundles. I'm not familiar with Symfony 2 / Doctrine 2 but a typical DDD tactic is to try and make sure that domain entities such as Order and Customer are unaware of bundle configurations. In other words, surrounding services should not add bundle-specific behaviors to entities. Delegating the responsibility for bundle awareness to entities will make them too complex. Fabricating entity class hierarchies to support extensive behavior is also too complex. Instead, this extensibility should be managed by application services. An application service would determine which bundles are loaded and orchestrate the appropriate entities as a result.
Another strategic pattern to consider is bounded contexts. Is it possible to partition your application into bounded contexts which align with the modules? For example, to address the $order-getShippingMethods() method you can create two BCs, one where there is an order model that has a getShippingMethods() method and another without it. Having two models may seem like a violation of DRY but if the models represent different things (ie an order that has shipping data vs an order that doesn't) then nothing is actually repeated.
I'm about to implement a web service for my database, perhaps using WCF Data Services. Some of the objects I need to make available have child objects that need to be present for the objects to be useful. But because of lazy loading in the Entity Framework, those child objects are not going to be automatically loaded.
I'm going to be calling this service using JSON, and I don't want to have to specify the $expand option in each call. And it's not clear to me where I would use the LoadProperty method (same link), since I'm just writing the InitializeService method and letting the framework do the rest.
Is there a way to configure it to explicitly load some child objects and not others?
WCF Data Services currently doesn't support auto-expand on the server. The client always has to ask for expansions.
You could implement some kind of a workaround around the WCF DS, by modifying the incoming request. So for example if the client sends request for ~/Products you could modify it before it gets to WCF DS and let it process ~/Products&$expand=Category and that way effectively achieve auto-expand. But for such a service to be robust, you would have to parse the query URL and only add the expand if there's not already one in there and so on.
The other way is if its always necessary for the child object to be present, can we make the child object complex types instead of entities, so that they always come along with the parent. Is there a strong reason for the child objects to be individual entities?
Hope this helps.
Thanks
Pratik
I have been reading about entity framework over the past couple of days and have managed to get a fair idea of using it but I still have a couple of questions some of which might seem a bit too basic. For perspective I am using entity framework 4.0 in an asp.net web application.If you can answer any of the questions please go ahead.
What advantage do I get by using POCO templates. I understand that if I wish to get persistence ignorance and keep my Entities clear of any information related to storage POCO entities are the way to go. Also I could switch from Entity framework to say NHibernate with relative ease when using POCO entities? Apart from loose coupling is there any significant reason for me to go towards POCO entities. Also if I do use POCO do I end up losing anything. I still get change tracking and lazy loading with the help of proxies?
Is it normal practice to use the Entities of the EF model as Data transfer Objects or Business Objects. i.e for example I have a separate class library for my entity model.Supposing I am using MVP , where I want a list of Employee's in a company. The presenter would request my business logic functions which would query the entity model for the list of Employee's and return the list of entities to the presenter. In this case my presenter would need to have a reference to the EF model. Is this the correct way? In the case of my asp.net web applciation it shouldnt be a problem but if I am using web services how does this work? Is this the reason to go towards POCO entities?
Supposing The Employee entity has a navigation property to a company table. If I use and wrap the data context in an 'using' block , and try to access the navigation property in the BL I am assuming I would get an exception. Would I also get an exception if I turned off lazyloading and used the 'include' linq query to get the entity? On a previous post someone recommended I use an context per request implying that the context remains active even when I am in the BL. I am assuming I would still need to detach the object and attach it to the context on my next request if I wish to persist any changes I make? or Instead should I just query for the object again with the new context and update it?
This question has more to do with organizing files/best practices and is a followup to a question i posted earlier. When I am using separate files based on entities to organize my data access layer, what is the best practice to organize my queries involving joins between multiple tables. I am still a bit hazy on organization. Have tried searching online but havent had much help.
Terrific question. My first recommendation is to think in patterns. With that said...
You pretty much nailed the advantages of using POCO. There are some distinct advantages to decoupling your business objects (POCO entities) from your data access layer. But the primary reason is like you said the ability to change or modify layers below. However using POCO you are essentially following the Code First (CF) approach. Personally, I consider it Code In Parallel depending upon your software development life cycle. You still have all the bells and whistles that data or model first approach have and some since you can extend the DbContext which is ObjectContext under the hood. I read an article, which I cannot seem to find, that CF is the future of Entity Framework. Lastly the nice thing with POCO is you are able to incorporate validation rules here or else where. You can also provide projections. Lets say you have Date of Birth but you want an Age property as well. That now becomes a no brainer as the Age property is ignored when mapping to the database.
Personally I create my own business objects (POCO) for large projects that tend to have a life of its own where change is a way of life. Another thought is scalability and maintainability. What if down the road I choose to split functionality between applications where, like you mentioned web services, functionality is now delivered from two disparate locations. If you have encapsulated your business objects and DAL within the same code block separation or scalability has now become a bit more complex. However, consider the project. It may be small with very little future change so no need to throw a grenade to kill a fly. At which time data first might be the way to go and let edmx file represent your objects. So don't marry yourself to one technology or one methodology/pattern. Do what makes sense for your time and business.
Using statements are perfectly fine. In fact I've recently been turned on to then wrapping that within a TransactionScope. If an error occurs rollbacks are inherent. Next, something to consider is the UnitOfWork. UnitOfWork pattern encapsulates a snapshot of what needs to be performed where the Data Context is the boundaries from which you work within. For each UnitOfWork you have a subject for which work is to be performed on. For example an Employee. So if you are to save Employee information to keep it simple you would make a call to the BL service or repository (which ever). There you pass in the Employee Id, perform some work under that UnitOfWork where it is either instantiated in the constructor or using Dependency Injections (DI or IoC). Easy starter is StructureMap. There the service makes the necessary calls to your UnitOfWork (DbContext) then returns control back upstream (e.g. UI).
The best way to learn here is to view others code. I'd start with some Microsoft examples. I'd start with Nerd Dinner (http://nerddinner.codeplex.com/) then build off that.
Additional Reading:
Use prototype pattern or not
http://weblogs.asp.net/manavi/archive/2011/05/17/associations-in-ef-4-1-code-first-part-6-many-valued-associations.aspx
[EDIT]
NightHawk457, I'm terribly sorry for not responding to your questions. Hopefully you figured it out but for future readers...
To help everyone visualize, imagine the below Architecture using the Domain Model and Repository as an example. Remember, there are many ways to skin a cat so take this and make it your own and don't forget my Grenade comment above.
Data Layer (Data Access): MyDbContext : DbContext, IUnitOfWork, where IUnitWork contracts the CRUD operations.
Data Repository (Data Access / Business Logic): MyDomainObjectRepository : IMyDomainObjectRepository, which receives IUnitOfWork by Factory class or Dependency Injection. Calls MyDomainObject validation on CRUD operations.
Domain Model (Business Logic): MyDomainObject using [Custom] Validation Attributes. Read this for pros/cons.
MVVM / MVC / WCF (Presentation / Service Layers): What ever additional layers you chose, you now have access to your data which is wrapped nicely in smaller modules who are self encapsulating of their function. The presentation layer (e.g. ViewModel, Controller, Code-Behind, etc.) can then receive an IMyObjectRepository by a Factory class or by Dependency Injection.
Tips:
Pass connection string into MyDbContext so you can reuse MyDbContext.
MySql does not play well with System.Transactions.TransactionScope, example. I don't recall exactly but it was something MySql did not support. This makes Testing a bit difficult since we have created this level of separation.
Create a Test project for each layer and at the minimum test general functionality/rules.
Each Domain Object should extend base object with ID field at minimum. Also do not implement Key attributes here. Domain Object should not describe architecture but rather the specific data as an entity. Even on Code First this can be achieved by the Fluent API.
Think generics when creating MyDbContext. ;) Read Diego's post.
In ASP.NET, the repositories are nice to use with ObjectDataSources.
As you can see, there is clear separation of roles where IUnitOfWork and IMyDomainObjectRepository are the Interfaces which expose the above layers functionality. And as an example, IUnitOfWork could be NHibernate, Entity Framework, LinqToSql or ADO.NET where a change to the factory class or dependency injection registration is all that has to change. FYI, I've heard the Repository called the Service Layer as well. Personally I like the first name to not be confused with Web Services. The next big take away from this structure is realizing the scope for you Database Context (IUnitOfWork). A simple example would be a ASP.NET page where for each page there is one and only one IUnitOfWork for either each repository or for that scope of work. Same holds true for ViewModels, Controllers, etc. So let's say you need to utilize two repositories, EmployeeRepository and HRRepository. You then could share the IUnitOfWork between both or not. To cross page, ViewModel or Controller boundaries, we use the ID for entities where they are then pulled from the DB and work is performed. You could alternatively pass a DTO across boundaries and attach to the context but then you begin losing separation of layers.
To continue, POCO classes do not have to be auto generated. In fact you can create your Entity Classes from scratch and perform the mapping in your extended DbContext class inside the OnModelCreating(DbModelBuilder mb) method. Start here, then here and note the Additional Resources, google Fluent API and read this post by Diego.
As for validation, this is an interesting point because it would be GREAT if all Business Rules could be validated in one location. Well, as we all know that doesn't work real well. So here is my recommendation, keep all data level validation (i.e. required, range, format, etc.) with data annotation as much as possible in the domain object and leave process validation in the Repository with clear roles of the Repository (i.e. if (isEmployee) do this, else that). I say clear, such that you do not want to add an Employee in two different Repositories where validation has to be duplicated. To call the validation, start here. Capture the ValidationResults and send upstream with a MyRepositoryValidationException which contains a collection of validations errors (e.g. Employee is required) which can be presented to the presentation layer. With all that said, don't forget to perform validation at the presentation layer. You don't want post backs to make sure an Employee has a valid Email, for example.
Just remember to balance time and effort with complexity. For something simple, use Data First or Model First with your EDMX file. Then lay a repository on top of that which also contains all the validation rules.
i am using EF4 and StructureMap in an asp.net web application. I am using the repository/unit of work patterns as detailed in this post. In the code, there is a line that delegates the setup of an ObjectContext in global.asax.
EntityUnitOfWorkFactory.SetObjectContext(() => new MyObjectContext());
On the web page code-behind, you can create a generic repository interface like so ...
IRepository<MyPocoObject> ds = ObjectFactory.GetInstance<IRepository<MyPocoObject>>();
My question is what is a good approach to refactoring this code so that I can use more than one ObjectContext and differentiate between them in the code-behind? Basically i have two databases/entity models in my application and need to query them both on the same page.
The Unit of Work is used to manage persistence across multiple repositories, not multiple object contexts.
You're not going to be able to persist changes across multiple contexts using a unit of work, as the UoW is simply implemented as a wrapper for a ObjectContext. Therefore, you'll need two unit of works.
Overall, things are going to get messy. You're going to have two OCs newed up and disposed each HTTP request, not to mention transaction management is going to be a nightmare.
Must you have two ObjectContexts? What is the reasoning for this? If it's for scalability, don't bother; it's going to be too painful for other things like your repository, unit of work and http scope management.
It's hard to provide good advice without seeing how you have your repositories set up.
Try creating wrapper classes for each object context, each implementing IUnitOfWork and a secondary unique interface (IEfSqlContext1, etc which represents one of your models/contexts).
Then you can inject whichever context you want.
As I said though, try and avoid having two EDMX/Contexts. It's more trouble than it's worth.