I am implementing a solution using EF code first, with Repository pattern and unit of work to do a correct separation. I am driving crazy trying to find the correct approach.
So my solution looks like:
DataAccess Project where I write my code first classes (Currenty I only have one: Posts.cs) and wrote my DBContext, y also added here other classes I needed for example for login and I marked them as [NotMapped](I know...it doesn't make sense)
Repository: Where I implemented Repository Pattern and Unit of Work
WCF service project: Here I access the unit of work like:
var posts= unitOfWork.PostRepository.Get()
here it's all good, but I might need to do this:
unitOfWork.PostRepository.Insert(Post)
and now all the purpose of decoupling dataAccess goes to shi** because I need to reference DataAccess project.
So, couple of questions:
Which is the best approach, how can I have a model separated?
I don't have a business layer, all logic like login to active directory, it's ok to put it in WCF project?
Please help!!!
The problem you're describing here took me a real long to get my head around a few years ago. You're definitely on the right track wanting to separate data access and business logic, and the business logic should be in its own project, so what you need to do is create an abstraction in the form of an repository interface. Something like:
interface IPostRepository
{
void Insert(Post post);
void Update(Post post);
void Delete(int postId);
Post GetById(int postId);
}
This interface must be placed in the business logic project, since your business logic needs to be able to read and write data.
In your data access you layer you implement this interface, so you will need to have a reference from the data access layer to the business logic, but not the other way around.
And finally, somewhere you need to tie the interface and the implementation together, and that should be done in the WCF service project, which means that it has references to both the data layer and the business layer. With this setup, you can have a WCF service method that looks something like below.
void InsertPost(Post post)
{
using (var db = new DbContext())
{
var postRepository = new PostRepository(db);
var postService = new PostService(postRepository);
postService.Insert(post);
db.SaveChanges();
}
}
Now this looks a bit strange since PostService seemingly has to know about PostRepository. But the constructor of PostService looks like this:
public PostService(IPostRepository postRepository)
{
_postRepository = postRepository;
}
The manual construction of PostRepository and PostService in the example above is far from ideal. I would really recommend that you take a look at an Inversion of Control container that makes most of this decoupling and layering a breeze. There are several out there: Autofac, Unity, Ninject etc.
I always used Repository pattern but for my latest project I wanted to see if I could perfect the use of it and my implementation of “Unit Of Work”. The more I started digging I started asking myself the question: "Do I really need it?"
Now this all starts with a couple of comments on Stackoverflow with a trace to Ayende Rahien's post on his blog, with 2 specific,
repository-is-the-new-singleton
ask-ayende-life-without-repositories-are-they-worth-living
This could probably be talked about forever and ever and it depends on different applications. Whats I like to know,
would this approach be suited for a Entity Framework project?
using this approach is the business logic still going in a service layer, or extension methods (as explained below, I know, the extension method is using NHib session)?
That's easily done using extension methods. Clean, simple and reusable.
public static IEnumerable GetAll(
this ISession instance, Expression<Func<T, bool>> where) where T : class
{
return instance.QueryOver().Where(where).List();
}
Using this approach and Ninject as DI, do I need to make the Context a interface and inject that in my controllers?
I've gone down many paths and created many implementations of repositories on different projects and... I've thrown the towel in and given up on it, here's why.
Coding for the exception
Do you code for the 1% chance your database is going to change from one technology to another? If you're thinking about your business's future state and say yes that's a possibility then a) they must have a lot of money to afford to do a migration to another DB technology or b) you're choosing a DB technology for fun or c) something has gone horribly wrong with the first technology you decided to use.
Why throw away the rich LINQ syntax?
LINQ and EF were developed so you could do neat stuff with it to read and traverse object graphs. Creating and maintain a repository that can give you the same flexibility to do that is a monstrous task. In my experience any time I've created a repository I've ALWAYS had business logic leak into the repository layer to either make queries more performant and/or reduce the number of hits to the database.
I don't want to create a method for every single permutation of a query that I have to write. I might as well write stored procedures. I don't want GetOrder, GetOrderWithOrderItem, GetOrderWithOrderItemWithOrderActivity, GetOrderByUserId, and so on... I just want to get the main entity and traverse and include the object graph as I so please.
Most examples of repositories are bullshit
Unless you are developing something REALLY bare-bones like a blog or something your queries are never going to be as simple as 90% of the examples you find on the internet surrounding the repository pattern. I cannot stress this enough! This is something that one has to crawl through the mud to figure out. There will always be that one query that breaks your perfectly thought out repository/solution that you've created, and it's not until that point where you second guess yourself and the technical debt/erosion begins.
Don't unit test me bro
But what about unit testing if I don't have a repository? How will I mock? Simple, you don't. Lets look at it from both angles:
No repository - You can mock the DbContext using an IDbContext or some other tricks but then you're really unit testing LINQ to Objects and not LINQ to Entities because the query is determined at runtime... OK so that's not good! So now it's up to the integration test to cover this.
With repository - You can now mock your repositories and unit test the layer(s) in between. Great right? Well not really... In the cases above where you have to leak logic into the repository layer to make queries more performant and/or less hits to the database, how can your unit tests cover that? It's now in the repo layer and you don't want to test IQueryable<T> right? Also let's be honest, your unit tests aren't going to cover the queries that have a 20 line .Where() clause and .Include()'s a bunch of relationships and hits the database again to do all this other stuff, blah, blah, blah anyways because the query is generated at runtime. Also since you created a repository to keep the upper layers persistence ignorant, if you now you want to change your database technology, sorry your unit tests are definitely not going to guarantee the same results at runtime, back to integration tests. So the whole point of the repository seems weird..
2 cents
We already lose a lot of functionality and syntax when using EF over plain stored procedures (bulk inserts, bulk deletes, CTEs, etc.) but I also code in C# so I don't have to type binary. We use EF so we can have the possibility of using different providers and to work with object graphs in a nice related way amongst many things. Certain abstractions are useful and some are not.
The repository pattern is an abstraction. It's purpose is to reduce complexity and make the rest of the code persistant ignorant. As a bonus it allows you to write unit tests instead of integration tests.
The problem is that many developers fail to understand the patterns purpose and create repositories which leak persistance specific information up to the caller (typically by exposing IQueryable<T>). By doing so they get no benefit over using the OR/M directly.
Update to address another answer
Coding for the exception
Using repositories is not about being able to switch persistence technology (i.e. changing database or using a webservice etc instead). It's about separating business logic from persistence to reduce complexity and coupling.
Unit tests vs integration tests
You do not write unit tests for repositories. period.
But by introducing repositories (or any other abstraction layer between persistance and business) you are able to write unit tests for the business logic. i.e. you do not have to worry about your tests failing due to an incorrectly configured database.
As for the queries. If you use LINQ you also have to make sure that your queries work, just as you have to do with repositories. and that is done using integration tests.
The difference is that if you have not mixed your business with LINQ statements you can be 100% sure that it's your persistence code that are failing and not something else.
If you analyze your tests you will also see that they are much cleaner if you have not mixed concerns (i.e. LINQ + Business logic)
Repository examples
Most examples are bullshit. that is very true. However, if you google any design pattern you will find a lot of crappy examples. That is no reason to avoid using a pattern.
Building a correct repository implementation is very easy. In fact, you only have to follow a single rule:
Do not add anything into the repository class until the very moment that you need it
A lot of coders are lazy and tries to make a generic repository and use a base class with a lot of methods that they might need. YAGNI. You write the repository class once and keep it as long as the application lives (can be years). Why fuck it up by being lazy. Keep it clean without any base class inheritance. It will make it much easier to read and maintain.
(The above statement is a guideline and not a law. A base class can very well be motivated. Just think before you add it, so that you add it for the right reasons)
Old stuff
Conclusion:
If you don't mind having LINQ statements in your business code nor care about unit tests I see no reason to not use Entity Framework directly.
Update
I've blogged both about the repository pattern and what "abstraction" really means: http://blog.gauffin.org/2013/01/repository-pattern-done-right/
Update 2
For single entity type with 20+ fields, how will you design query method to support any permutation combination? You dont want to limit search only by name, what about searching with navigation properties, list all orders with item with specific price code, 3 level of navigation property search. The whole reason IQueryable was invented was to be able to compose any combination of search against database. Everything looks great in theory, but user's need wins above theory.
Again: An entity with 20+ fields is incorrectly modeled. It's a GOD entity. Break it down.
I'm not arguing that IQueryable wasn't made for quering. I'm saying that it's not right for an abstraction layer like Repository pattern since it's leaky. There is no 100% complete LINQ To Sql provider (like EF).
They all have implementation specific things like how to use eager/lazy loading or how to do SQL "IN" statements. Exposing IQueryable in the repository forces the user to know all those things. Thus the whole attempt to abstract away the data source is a complete failure. You just add complexity without getting any benefit over using the OR/M directly.
Either implement Repository pattern correctly or just don't use it at all.
(If you really want to handle big entities you can combine the Repository pattern with the Specification pattern. That gives you a complete abstraction which also is testable.)
IMO both the Repository abstraction and the UnitOfWork abstraction have a very valuable place in any meaningful development. People will argue about implementation details, but just as there are many ways to skin a cat, there are many ways to implement an abstraction.
Your question is specifically to use or not to use and why.
As you have no doubt realised you already have both these patterns built into Entity Framework, DbContext is the UnitOfWork and DbSet is the Repository. You don’t generally need to unit test the UnitOfWork or Repository themselves as they are simply facilitating between your classes and the underlying data access implementations. What you will find yourself needing to do, again and again, is mock these two abstractions when unit testing the logic of your services.
You can mock, fake or whatever with external libraries adding layers of code dependencies (that you don’t control) between the logic doing the testing and the logic being tested.
So a minor point is that having your own abstraction for UnitOfWork and Repository gives you maximum control and flexibility when mocking your unit tests.
All very well, but for me, the real power of these abstractions is they provide a simple way to apply Aspect Oriented Programming techniques and adhere to the SOLID principles.
So you have your IRepository:
public interface IRepository<T>
where T : class
{
T Add(T entity);
void Delete(T entity);
IQueryable<T> AsQueryable();
}
And its implementation:
public class Repository<T> : IRepository<T>
where T : class
{
private readonly IDbSet<T> _dbSet;
public Repository(PPContext context)
{
_dbSet = context.Set<T>();
}
public T Add(T entity)
{
return _dbSet.Add(entity);
}
public void Delete(T entity)
{
_dbSet.Remove(entity);
}
public IQueryable<T> AsQueryable()
{
return _dbSet.AsQueryable();
}
}
Nothing out of the ordinary so far but now we want to add some logging - easy with a logging Decorator.
public class RepositoryLoggerDecorator<T> : IRepository<T>
where T : class
{
Logger logger = LogManager.GetCurrentClassLogger();
private readonly IRepository<T> _decorated;
public RepositoryLoggerDecorator(IRepository<T> decorated)
{
_decorated = decorated;
}
public T Add(T entity)
{
logger.Log(LogLevel.Debug, () => DateTime.Now.ToLongTimeString() );
T added = _decorated.Add(entity);
logger.Log(LogLevel.Debug, () => DateTime.Now.ToLongTimeString());
return added;
}
public void Delete(T entity)
{
logger.Log(LogLevel.Debug, () => DateTime.Now.ToLongTimeString());
_decorated.Delete(entity);
logger.Log(LogLevel.Debug, () => DateTime.Now.ToLongTimeString());
}
public IQueryable<T> AsQueryable()
{
return _decorated.AsQueryable();
}
}
All done and with no change to our existing code. There are numerous other cross cutting concerns we can add, such as exception handling, data caching, data validation or whatever and throughout our design and build process the most valuable thing we have that enables us to add simple features without changing any of our existing code is our IRepository abstraction.
Now, many times I have seen this question on StackOverflow – “how do you make Entity Framework work in a multi tenant environment?”.
https://stackoverflow.com/search?q=%5Bentity-framework%5D+multi+tenant
If you have a Repository abstraction then the answer is “it’s easy add a decorator”
public class RepositoryTennantFilterDecorator<T> : IRepository<T>
where T : class
{
//public for Unit Test example
public readonly IRepository<T> _decorated;
public RepositoryTennantFilterDecorator(IRepository<T> decorated)
{
_decorated = decorated;
}
public T Add(T entity)
{
return _decorated.Add(entity);
}
public void Delete(T entity)
{
_decorated.Delete(entity);
}
public IQueryable<T> AsQueryable()
{
return _decorated.AsQueryable().Where(o => true);
}
}
IMO you should always place a simple abstraction over any 3rd party component that will be referenced in more than a handful of places. From this perspective an ORM is the perfect candidate as it is referenced in so much of our code.
The answer that normally comes to mind when someone says “why should I have an abstraction (e.g. Repository) over this or that 3rd party library” is “why wouldn’t you?”
P.S. Decorators are extremely simple to apply using an IoC Container, such as SimpleInjector.
[TestFixture]
public class IRepositoryTesting
{
[Test]
public void IRepository_ContainerRegisteredWithTwoDecorators_ReturnsDecoratedRepository()
{
Container container = new Container();
container.RegisterLifetimeScope<PPContext>();
container.RegisterOpenGeneric(
typeof(IRepository<>),
typeof(Repository<>));
container.RegisterDecorator(
typeof(IRepository<>),
typeof(RepositoryLoggerDecorator<>));
container.RegisterDecorator(
typeof(IRepository<>),
typeof(RepositoryTennantFilterDecorator<>));
container.Verify();
using (container.BeginLifetimeScope())
{
var result = container.GetInstance<IRepository<Image>>();
Assert.That(
result,
Is.InstanceOf(typeof(RepositoryTennantFilterDecorator<Image>)));
Assert.That(
(result as RepositoryTennantFilterDecorator<Image>)._decorated,
Is.InstanceOf(typeof(RepositoryLoggerDecorator<Image>)));
}
}
}
First of all, as suggested by some answer, EF itself is a repository pattern, there is no need to create further abstraction just to name it as repository.
Mockable Repository for Unit Tests, do we really need it?
We let EF communicate to test DB in unit tests to test our business logic straight against SQL test DB. I don't see any benefit of having mock of any repository pattern at all. What is really wrong doing unit tests against test database? As it is bulk operations are not possible and we end up writing raw SQL. SQLite in memory is perfect candidate for doing unit tests against real database.
Unnecessary Abstraction
Do you want to create repository just so that in future you can easily replace EF with NHbibernate etc or anything else? Sounds great plan, but is it really cost effective?
Linq kills unit tests?
I will like to see any examples on how it can kill.
Dependency Injection, IoC
Wow these are great words, sure they look great in theory, but sometimes you have to choose trade off between great design and great solution. We did use all of that, and we ended up throwing all at trash and choosing different approach. Size vs Speed (Size of code and Speed of development) matters huge in real life. Users need flexibility, they don't care if your code is great in design in terms of DI or IoC.
Unless you are building Visual Studio
All these great design are needed if you are building a complex program like Visual Studio or Eclipse which will be developed by many people and it needs to be highly customizable. All great development pattern came into picture after years of development these IDEs has gone through, and they have evolved at place where all these great design patterns matter so much. But if you are doing simple web based payroll, or simple business app, it is better that you evolve in your development with time, instead of spending time to build it for million users where it will be only deployed for 100s of users.
Repository as Filtered View - ISecureRepository
On other side, repository should be a filtered view of EF which guards access to data by applying necessary filler based on current user/role.
But doing so complicates repository even more as it ends up in huge code base to maintain. People end up creating different repositories for different user types or combination of entity types. Not only this, we also end up with lots of DTOs.
Following answer is an example implementation of Filtered Repository without creating whole set of classes and methods. It may not answer question directly but it can be useful in deriving one.
Disclaimer: I am author of Entity REST SDK.
http://entityrestsdk.codeplex.com
Keeping above in mind, we developed a SDK which creates repository of filtered view based on SecurityContext which holds filters for CRUD operations. And only two kinds of rules simplify any complex operations. First is access to entity, and other is Read/Write rule for property.
The advantage is, that you do not rewrite business logic or repositories for different user types, you just simply block or grant them the access.
public class DefaultSecurityContext : BaseSecurityContext {
public static DefaultSecurityContext Instance = new DefaultSecurityContext();
// UserID for currently logged in User
public static long UserID{
get{
return long.Parse( HttpContext.Current.User.Identity.Name );
}
}
public DefaultSecurityContext(){
}
protected override void OnCreate(){
// User can access his own Account only
var acc = CreateRules<Account>();
acc.SetRead( y => x=> x.AccountID == UserID ) ;
acc.SetWrite( y => x=> x.AccountID == UserID );
// User can only modify AccountName and EmailAddress fields
acc.SetProperties( SecurityRules.ReadWrite,
x => x.AccountName,
x => x.EmailAddress);
// User can read AccountType field
acc.SetProperties<Account>( SecurityRules.Read,
x => x.AccountType);
// User can access his own Orders only
var order = CreateRules<Order>();
order.SetRead( y => x => x.CustomerID == UserID );
// User can modify Order only if OrderStatus is not complete
order.SetWrite( y => x => x.CustomerID == UserID
&& x.OrderStatus != "Complete" );
// User can only modify OrderNotes and OrderStatus
order.SetProperties( SecurityRules.ReadWrite,
x => x.OrderNotes,
x => x.OrderStatus );
// User can not delete orders
order.SetDelete(order.NotSupportedRule);
}
}
These LINQ Rules are evaluated against Database in SaveChanges method for every operation, and these Rules act as Firewall in front of Database.
There is a lot of debate over which method is correct, so I look at it as both are acceptable so I use ever which one I like the most (Which is no repository, UoW).
In EF UoW is implemented via DbContext and the DbSets are repositories.
As for how to work with the data layer I just directly work on the DbContext object, for complex queries I will make extension methods for the query that can be reused.
I believe Ayende also has some posts about how abstracting out CUD operations is bad.
I always make an interface and have my context inherit from it so I can use an IoC container for DI.
What most apply over EF is not a Repository Pattern. It is a Facade pattern (abstracting the calls to EF methods into simpler, easier to use versions).
EF is the one applying the Repository Pattern (and the Unit of Work pattern as well). That is, EF is the one abstracting the data access layer so that the user has no idea they are dealing with SQLServer.
And at that, most "repositories" over EF are not even good Facades as they merely map, quite straightforwardly, to single methods in EF, even to the point of having the same signatures.
The two reasons, then, for applying this so-called "Repository" pattern over EF is to allow easier testing and to establish a subset of "canned" calls to it. Not bad in themselves, but clearly not a Repository.
Linq is a nowadays 'Repository'.
ISession+Linq already is the repository, and you need neither GetXByY methods nor QueryData(Query q) generalization. Being a little paranoid to DAL usage, I still prefer repository interface. (From maintainability point of view we also still have to have some facade over specific data access interfaces).
Here is repository we use - it de-couples us from direct usage of nhibernate, but provides linq interface (as ISession access in exceptional cases, which are subject to refactor eventually).
class Repo
{
ISession _session; //via ioc
IQueryable<T> Query()
{
return _session.Query<T>();
}
}
The Repository (or however one chooses to call it) at this time for me is mostly about abstracting away the persistence layer.
I use it coupled with query objects so I do not have a coupling to any particular technology in my applications. And also it eases testing a lot.
So, I tend to have
public interface IRepository : IDisposable
{
void Save<TEntity>(TEntity entity);
void SaveList<TEntity>(IEnumerable<TEntity> entities);
void Delete<TEntity>(TEntity entity);
void DeleteList<TEntity>(IEnumerable<TEntity> entities);
IList<TEntity> GetAll<TEntity>() where TEntity : class;
int GetCount<TEntity>() where TEntity : class;
void StartConversation();
void EndConversation();
//if query objects can be self sustaining (i.e. not need additional configuration - think session), there is no need to include this method in the repository.
TResult ExecuteQuery<TResult>(IQueryObject<TResult> query);
}
Possibly add async methods with callbacks as delegates.
The repo is easy to implement generically, so I am able not to touch a line of the implementation from app to app. Well, this is true at least when using NH, I did it also with EF, but made me hate EF. 4. The conversation is the start of a transaction. Very cool if a few classes share the repository instance. Also, for NH, one repo in my implementation equals one session which is opened at the first request.
Then the Query Objects
public interface IQueryObject<TResult>
{
/// <summary>Provides configuration options.</summary>
/// <remarks>
/// If the query object is used through a repository this method might or might not be called depending on the particular implementation of a repository.
/// If not used through a repository, it can be useful as a configuration option.
/// </remarks>
void Configure(object parameter);
/// <summary>Implementation of the query.</summary>
TResult GetResult();
}
For the configure I use in NH only to pass in the ISession. In EF makes no sense more or less.
An example query would be.. (NH)
public class GetAll<TEntity> : AbstractQueryObject<IList<TEntity>>
where TEntity : class
{
public override IList<TEntity> GetResult()
{
return this.Session.CreateCriteria<TEntity>().List<TEntity>();
}
}
To do an EF query you would have to have the context in the Abstract base, not the session. But of course the ifc would be the same.
In this way the queries are themselves encapsulated, and easily testable. Best of all, my code relies only on interfaces. Everything is very clean. Domain (business) objects are just that, e.g. there is no mixing of responsibilities like when using the active record pattern which is hardly testable and mixes data access (query) code in the domain object and in doing so is mixing concerns (object which fetches itself??). Everybody is still free to create POCOs for data transfer.
All in all, much code reuse and simplicity is provided with this approach at the loss of not anything I can imagine. Any ideas?
And thanks a lot to Ayende for his great posts and continued dedication. Its his ideas here (query object), not mine.
For me, it's a simple decision, with relatively few factors. The factors are:
Repositories are for domain classes.
In some of my apps, domain classes are the same as my persistence (DAL) classes, in others they are not.
When they are the same, EF is providing me with Repositories already.
EF provides lazy loading and IQueryable. I like these.
Abstracting/'facading'/re-implementing repository over EF usually means loss of lazy and IQueryable
So, if my app can't justify #2, separate domain and data models, then I usually won't bother with #5.
Having seen some strong advice against testing EF against mocks, especially Code First, I have decided to go with integration testing against a SqlCe database dedicated to testing, and then use pure unit tests further downstream from the unit of work and repositories provided by DbContext and DbSet.
I am just unclear where to draw the line and what to test where. I know I can mock the DAL in my service layer when I am confident the DAL specific integration tests cover its insides, but what do I test in the DAL? There doesn't seem to be much point testing to see if I can save and read an object, because EF is external and already tested.
You will test your mapping and queries in DAL by using integration tests. Example:
public class Service {
private readonly IDAL _dal;
public Service(IDAL dal) {
// Not null validation here
_dal = dal;
}
public void DoSomething() {
SomeData data = FindSomeData();
// Do some logic
_dal.Commit();
}
protected virtual SomeData FindSomeData() {
return _dal.SomeData.Where(...).FirstOrDefault();
}
}
This is very simplified example showing:
Service dependent on DAL. DAL interface is passed through constructor injection.
The Service contains public DoSomething method you want to test to know if the logic is executed correctly. But this method is also dependent on DB query and DB persistence (Commit).
The query is part of your logic but executing such query is separate concern so it is handled by its own method. In more complex situation this method can be in other class injected to the Service class (repository). The key criteria for these query methods are:
They don't return IQueryable
They don't accept Expression<> as parameters
How to unit test DoSomething method:
In this simple example your test class will derive from Service class and override FindSomeData to return test data. In case of injection you would instead define fake for injected class.
You will also mock IDAL and you can verify that Commit was called
What integration test you should use:
You should create test for FindSomeData querying the real database
In general you should also have integration test for Commit but it is more difficult to achieve because the example has commit called directly from DoSomething. You don't want to test that method again and in the same time Commit method has too much generic cases because it simply flushes all changes from current context to database. I usually have separate tests for inserting, updating and deleting every entity type. When the DoSomething method does some complex modification you can split the method into two methods one handled by unit test for a real logic and second covered by integration tests for different persistence scenarios which can be produced by your logic.
Entity Framework is tested, but your DAL, especially mapping, is not. I prefer having integration tests to show me that at the very least my mapping is right, and better yet, that I can successfully perform all CRUD operations against my database.
What we usually test DB-wise, is if the complex object graphs can be properly inserted, updated, deleted; basically testing the more complex mappings.
In my opinion there's not really much point in testing if an object with 3 primitive value properties can be inserted and whatnot, because then you'd never see the end of it.
We kind of favor being optimistic (that the simple stuff will just work), we test the more complex associations, and if we encounter an error in our mapping (e.g. an object that should be deleted but isn't) we write an extra test for that.
It's usually not wise to test absolutely everything from a business perspective; you should focus on the high-risk/high-damage stuff first and then work your way down the severity ladder until you think it's not worth it anymore.
1) Have a set of integration tests which test your mappings
2) Make your DAL very light weight but with sufficent power to construct querys, something like:
public interface IDb
{
IQueryable<T>Query<T>();
... (save, delete, get-by-id methods)...
}
3) Write objects which encapsulate the logic behind constructing the query against the DAL
public class MuppetSearch
{
public MuppetColor? Color { get; set;}
public string Name{ get; set; }
public IQueryable<Muppet> ConstructQuery(IDb db)
{
var query = db.Query<Muppet>();
if(Color.HasValue)
{
query = query.Where(m=>m.Value == Color.Value);
}
if(!String.IsNullOrEmpty(Name))
{
query = query.Where(m=>m.Name.Contains(Name));
}
return query;
}
}
4) Test those, mocking all the data you need should be pretty trivial
5) In your service use the search classes to do your query construction
Recently I was looking at some source code provided by community leaders in their open source implementations. One these projects made use of IOC. Here is sample hypothetical code:
public class Class1
{
private ISomeInterface _someObject;
public Class1(ISomeInterface someObject)
{
_someObject = someObject;
}
// some more code and then
var someOtherObject = new SomeOtherObject();
}
My question is not about what the IOCs are for and how to use them in technical terms but rather what are the guidelines regarding object creation. All that effort and then this line using "new" operator. I don't quite understand. Which object should be created by IOC and for which ones it is permissible to be created via the new operator?
As a general rule of thumb, if something is providing a service which may want to be replaced either for testing or to use a different implementation (e.g. different authentication services) then inject the dependency. If it's something like a collection, or a simple data object which isn't providing behaviour which you'd ever want to vary, then it's fine to instantiate it within the class.
Usually you use IoC because:
A dependency that can change in the future
To code against interfaces, not concrete types
To enable mocking these dependencies in Unit Testing scenarios
You could avoid using IoC in the case where you don't control the dependency, for example an StringBuilder is always going to be an StringBuilder and have a defined behavior, and you usually don't really need to mock that; while you might want to mock an HttpRequestBase, because it's an external dependency on having an internet connection, for example, which is a problem during unit tests (longer execution times, and it's something out of your control).
The same happens for database access repositories and so on.
I am working in a project that has two main parts: a class library assembly and the main application. Both are using Castle Windsor for IoC and both manually setup their list of of components in code (to aid refactoring and prevent the need for a config file). Currently the main application has code like this:
public static void Main()
{
// Perform library IoC setup
LibraryComponent.Init();
// Perform application IoC setup
IoC.Register<IXyz, Abc>("abc");
// etc, etc, ...
// Start the application code ...
}
However the call to initialise the library doesn't seem like a good solution. What is the best way to setup a class library that uses an IoC container to decouple its internal components?
Edit:
Lusid proposed using a static method on each public component in the library that would in turn make the call to initialise. One possible way to make this a bit nicer would be to use something like PostSharp to do this in an aspect-oriented way. However I was hoping for something a bit more elegant ;-)
Lusid also proposed using the AppDomain.AssemblyLoad event to perform custom steps at load time, however I am really after a way to avoid the client assembly from requiring any setup code.
Thanks!
I'm not sure if I'm understanding exactly the problem you are trying to solve, but my first guess is that you are looking for a way to decouple the need to call the Init method from your main application.
One method I've used in the past is a static constructor on a static class in the class library:
static public class LibraryComponent {
static LibraryComponent() {
Init();
}
}
If you have multiple class libraries, and would like a quick and dirty way of evaluating all of them as they are loaded, here's a (kinda hairy) way:
[STAThread]
static void Main()
{
AppDomain.CurrentDomain.AssemblyLoad += new AssemblyLoadEventHandler(CurrentDomain_AssemblyLoad);
}
static void CurrentDomain_AssemblyLoad(object sender, AssemblyLoadEventArgs args)
{
IEnumerable<Type> types = args.LoadedAssembly.GetTypes()
.Where(t => typeof(IMyModuleInterface).IsAssignableFrom(t));
foreach (Type t in types)
{
doSomethingWithType(t);
}
}
The Where clause could be anything you want, of course. The code above would find any class deriving from IMyModuleInterface in each assembly that gets loaded into the current AppDomain, and then I can do something with it, whether it be registering dependencies, maintaining an internal list, whatever.
Might not be exactly what you are looking for, but hopefully it helps in some way.
You could have a registration module. Basically LibraryComponent.Init() function takes an IRegistrar to wire everything up.
The IRegistrar could basically have a function Register(Type interface, Type implementation). The implimentor would map that function back to their IOC container.
The downside is that you can't rely on anything specific to the container your using.
Castle Windsor actually has a concept called facilities that are basically just ways of wrapping standardised pieces of configuration. In this model, you would simply add the two facilities to the container and they would do the work.
Of course, this wouldn't really be better than calling a library routine to do the work unless you configured the facilities in a configuration file (consider binsor). If you are really allergic to configuration files, your current solution is probably the best.