I am using uow and repository pattern.
I have having trouble configuring what is the right way to perform queries in methods that are called from the main methods.
To make it clear:
I have some Method:
GetSomthingFromDB(int someId)
{
using (var uow = new UnitOfWork())
{
//Get the study from Db withrelated Entities
IRepository<Study> studyRepository
=uow.GetRepository<Study();
Foreach(var finding in study.Findings)
{
SomeSubMethod(finding);
}
}
}
SomeSubMethod(Finding finding)
{
//Do all kind of stuff on a finding
}
OK, now in SomeSubMethod(), I need to get something from the Db, Lets say something from configuration table.
But I don't have uow inside the subMethod (could be that subMethods calls another subMethod, and Only there I need the uow again.
Should I pass uow from one Method to the other?
Should I pass the repository inner and inner?
Should I Use uow as a class member?
What is the best practice?
Thank you. Tal.
General info:
Keep the connection live cycle short as possbile
if you are using WPF or ASP view then you can keep the connection (uow) alive as long the view is active.
Desgin your methods with SRP
Should I pass uow from one Method to the other?
Yes, some times you need to pass the unitOfWork form method to other one.
You can pass it on private without any problem
If you pass it to a public method you have to take care about the method scope usage to avoid any concurrency issues.
Should I pass the repository inner and inner?
Same here repostiory belogn to a connection and, if your method is public and called from differents layers/threads, then you might get some concurrency issues.
Should I Use uow as a class member?
Yes, and the best thing if you pass it on the constuctor as parameter and without a setter.
I am about to implement an Entity Framework 6 design with a repository and unit of work.
There are so many articles around and I'm not sure what the best advice is: For example I realy like the pattern implemented here: for the reasons suggested in the article here
However, Tom Dykstra (Senior Programming Writer on Microsoft's Web Platform & Tools Content Team) suggests it should be done in another article: here
I subscribe to Pluralsight, and it is implemented in a slightly different way pretty much every time it is used in a course so choosing a design is difficult.
Some people seem to suggest that unit of work is already implemented by DbContext as in this post, so we shouldn't need to implement it at all.
I realise that this type of question has been asked before and this may be subjective but my question is direct:
I like the approach in the first (Code Fizzle) article and wanted to know if it is perhaps more maintainable and as easily testable as other approaches and safe to go ahead with?
Any other views are more than welcome.
#Chris Hardie is correct, EF implements UoW out of the box. However many people overlook the fact that EF also implements a generic repository pattern out of the box too:
var repos1 = _dbContext.Set<Widget1>();
var repos2 = _dbContext.Set<Widget2>();
var reposN = _dbContext.Set<WidgetN>();
...and this is a pretty good generic repository implementation that is built into the tool itself.
Why go through the trouble of creating a ton of other interfaces and properties, when DbContext gives you everything you need? If you want to abstract the DbContext behind application-level interfaces, and you want to apply command query segregation, you could do something as simple as this:
public interface IReadEntities
{
IQueryable<TEntity> Query<TEntity>();
}
public interface IWriteEntities : IReadEntities, IUnitOfWork
{
IQueryable<TEntity> Load<TEntity>();
void Create<TEntity>(TEntity entity);
void Update<TEntity>(TEntity entity);
void Delete<TEntity>(TEntity entity);
}
public interface IUnitOfWork
{
int SaveChanges();
}
You could use these 3 interfaces for all of your entity access, and not have to worry about injecting 3 or more different repositories into business code that works with 3 or more entity sets. Of course you would still use IoC to ensure that there is only 1 DbContext instance per web request, but all 3 of your interfaces are implemented by the same class, which makes it easier.
public class MyDbContext : DbContext, IWriteEntities
{
public IQueryable<TEntity> Query<TEntity>()
{
return Set<TEntity>().AsNoTracking(); // detach results from context
}
public IQueryable<TEntity> Load<TEntity>()
{
return Set<TEntity>();
}
public void Create<TEntity>(TEntity entity)
{
if (Entry(entity).State == EntityState.Detached)
Set<TEntity>().Add(entity);
}
...etc
}
You now only need to inject a single interface into your dependency, regardless of how many different entities it needs to work with:
// NOTE: In reality I would never inject IWriteEntities into an MVC Controller.
// Instead I would inject my CQRS business layer, which consumes IWriteEntities.
// See #MikeSW's answer for more info as to why you shouldn't consume a
// generic repository like this directly by your web application layer.
// See http://www.cuttingedge.it/blogs/steven/pivot/entry.php?id=91 and
// http://www.cuttingedge.it/blogs/steven/pivot/entry.php?id=92 for more info
// on what a CQRS business layer that consumes IWriteEntities / IReadEntities
// (and is consumed by an MVC Controller) might look like.
public class RecipeController : Controller
{
private readonly IWriteEntities _entities;
//Using Dependency Injection
public RecipeController(IWriteEntities entities)
{
_entities = entities;
}
[HttpPost]
public ActionResult Create(CreateEditRecipeViewModel model)
{
Mapper.CreateMap<CreateEditRecipeViewModel, Recipe>()
.ForMember(r => r.IngredientAmounts, opt => opt.Ignore());
Recipe recipe = Mapper.Map<CreateEditRecipeViewModel, Recipe>(model);
_entities.Create(recipe);
foreach(Tag t in model.Tags) {
_entities.Create(tag);
}
_entities.SaveChanges();
return RedirectToAction("CreateRecipeSuccess");
}
}
One of my favorite things about this design is that it minimizes the entity storage dependencies on the consumer. In this example the RecipeController is the consumer, but in a real application the consumer would be a command handler. (For a query handler, you would typically consume IReadEntities only because you just want to return data, not mutate any state.) But for this example, let's just use RecipeController as the consumer to examine the dependency implications:
Say you have a set of unit tests written for the above action. In each of these unit tests, you new up the Controller, passing a mock into the constructor. Then, say your customer decides they want to allow people to create a new Cookbook or add to an existing one when creating a new recipe.
With a repository-per-entity or repository-per-aggregate interface pattern, you would have to inject a new repository instance IRepository<Cookbook> into your controller constructor (or using #Chris Hardie's answer, write code to attach yet another repository to the UoW instance). This would immediately make all of your other unit tests break, and you would have to go back to modify the construction code in all of them, passing yet another mock instance, and widening your dependency array. However with the above, all of your other unit tests will still at least compile. All you have to do is write additional test(s) to cover the new cookbook functionality.
I'm (not) sorry to say that the codefizzle, Dyksta's article and the previous answers are wrong. For the simple fact that they use the EF entities as domain (business) objects, which is a big WTF.
Update: For a less technical explanation (in plain words) read Repository Pattern for Dummies
In a nutshell, ANY repository interface should not be coupled to ANY persistence (ORM) detail. The repo interface deals ONLY with objects that makes sense for the rest of the app (domain, maybe UI as in presentation). A LOT of people (with MS leading the pack, with intent I suspect) make the mistake of believing that they can reuse their EF entities or that can be business object on top of them.
While it can happen, it's quite rare. In practice, you'll have a lot of domain objects 'designed' after database rules i.e bad modelling. The repository purpose is to decouple the rest of the app (mainly the business layer) from its persistence form.
How do you decouple it when your repo deals with EF entities (persistence detail) or its methods return IQueryable, a leaking abstraction with wrong semantics for this purpose (IQueryable allows you to build a query, thus implying that you need to know persistence details thus negating the repository's purpose and functionality)?
A domin object should never know about persistence, EF, joins etc. It shouldn't know what db engine you're using or if you're using one. Same with the rest of the app, if you want it to be decoupled from the persistence details.
The repository interface know only about what the higher layer know. This means, that a generic domain repository interface looks like this
public interface IStore<TDomainObject> //where TDomainObject != Ef (ORM) entity
{
void Save(TDomainObject entity);
TDomainObject Get(Guid id);
void Delete(Guid id);
}
The implementation will reside in the DAL and will use EF to work with the db. However the implementation looks like this
public class UsersRepository:IStore<User>
{
public UsersRepository(DbContext db) {}
public void Save(User entity)
{
//map entity to one or more ORM entities
//use EF to save it
}
//.. other methods implementation ...
}
You don't really have a concrete generic repository. The only usage of a concrete generic repository is when ANY domain object is stored in serialized form in a key-value like table. It isn't the case with an ORM.
What about querying?
public interface IQueryUsers
{
PagedResult<UserData> GetAll(int skip, int take);
//or
PagedResult<UserData> Get(CriteriaObject criteria,int skip, int take);
}
The UserData is the read/view model fit for the query context usage.
You can use directly EF for querying in a query handler if you don't mind that your DAL knows about view models and in that case you won't be needing any query repo.
Conclusion
Your business object shouldn't know about EF entities.
The repository will use an ORM, but it never exposes the ORM to the rest of the app, so the repo interface will use only domain objects or view models (or any other app context object that isn't a persistence detail)
You do not tell the repo how to do its work i.e NEVER use IQueryable with a repo interface
If you just want to use the db in a easier/cool way and you're dealing with a simple CRUD app where you don't need (be sure about it) to maintain separation of concerns then skip the repository all together, use directly EF for everything data. The app will be tightly coupled to EF but at least you'll cut the middle man and it will be on purpose not by mistake.
Note that using the repository in the wrong way, will invalidate its use and your app will still be tightly coupled to the persistence (ORM).
In case you believe the ORM is there to magically store your domain objects, it's not. The ORM purpose is to simulate an OOP storage on top of relational tables. It has everything to do with persistence and nothing to do with domain, so don't use the ORM outside persistence.
DbContext is indeed built with the Unit of Work pattern. It allows all of its entities to share the same context as we work with them. This implementation is internal to the DbContext.
However, it should be noted that if you instantiate two DbContext objects, neither of them will see the other's entities that they are each tracking. They are insulated from one another, which can be problematic.
When I build an MVC application, I want to ensure that during the course of the request, all my data access code works off of a single DbContext. To achieve that, I apply the Unit of Work as a pattern external to DbContext.
Here is my Unit of Work object from a barbecue recipe app I'm building:
public class UnitOfWork : IUnitOfWork
{
private BarbecurianContext _context = new BarbecurianContext();
private IRepository<Recipe> _recipeRepository;
private IRepository<Category> _categoryRepository;
private IRepository<Tag> _tagRepository;
public IRepository<Recipe> RecipeRepository
{
get
{
if (_recipeRepository == null)
{
_recipeRepository = new RecipeRepository(_context);
}
return _recipeRepository;
}
}
public void Save()
{
_context.SaveChanges();
}
**SNIP**
I attach all my repositories, which are all injected with the same DbContext, to my Unit of Work object. So long as any repositories are requested from the Unit of Work object, we can be assured that all our data access code will be managed with the same DbContext - awesome sauce!
If I were to use this in an MVC app, I would ensure the Unit of Work is used throughout the request by instantiating it in the controller, and using it throughout its actions:
public class RecipeController : Controller
{
private IUnitOfWork _unitOfWork;
private IRepository<Recipe> _recipeService;
private IRepository<Category> _categoryService;
private IRepository<Tag> _tagService;
//Using Dependency Injection
public RecipeController(IUnitOfWork unitOfWork)
{
_unitOfWork = unitOfWork;
_categoryRepository = _unitOfWork.CategoryRepository;
_recipeRepository = _unitOfWork.RecipeRepository;
_tagRepository = _unitOfWork.TagRepository;
}
Now in our action, we can be assured that all our data access code will use the same DbContext:
[HttpPost]
public ActionResult Create(CreateEditRecipeViewModel model)
{
Mapper.CreateMap<CreateEditRecipeViewModel, Recipe>().ForMember(r => r.IngredientAmounts, opt => opt.Ignore());
Recipe recipe = Mapper.Map<CreateEditRecipeViewModel, Recipe>(model);
_recipeRepository.Create(recipe);
foreach(Tag t in model.Tags){
_tagRepository.Create(tag); //I'm using the same DbContext as the recipe repo!
}
_unitOfWork.Save();
Searching around the internet I found this http://www.thereformedprogrammer.net/is-the-repository-pattern-useful-with-entity-framework/ it's a 2 part article about the usefulness of the repository pattern by Jon Smith.
The second part focuses on a solution. Hope it helps!
Repository with unit of work pattern implementation is a bad one to answer your question.
The DbContext of the entity framework is implemented by Microsoft according to the unit of work pattern. That means the context.SaveChanges is transactionally saving your changes in one go.
The DbSet is also an implementation of the Repository pattern. Do not build repositories that you can just do:
void Add(Customer c)
{
_context.Customers.Add(c);
}
Create a one-liner method for what you can do inside the service anyway ???
There is no benefit and nobody is changing EF ORM to another ORM nowadays...
You do not need that freedom...
Chris Hardie is argumenting that there could be instantiated multiple context objects but already doing this you do it wrong...
Just use an IOC tool you like and setup the MyContext per Http Request and your are fine.
Take ninject for example:
kernel.Bind<ITeststepService>().To<TeststepService>().InRequestScope().WithConstructorArgument("context", c => new ITMSContext());
The service running the business logic gets the context injected.
Just keep it simple stupid :-)
You should consider "command/query objects" as an alternative, you can find a bunch of interesting articles around this area, but here is a good one:
https://rob.conery.io/2014/03/03/repositories-and-unitofwork-are-not-a-good-idea/
When you need a transaction over multiple DB objects, use one command object per command to avoid the complexity of the UOW pattern.
A query object per query is likely unnecessary for most projects. Instead you might choose to start with a 'FooQueries' object
...by which I mean you can start with a Repository pattern for READS but name it as "Queries" to be explicit that it does not and should not do any inserts/updates.
Later, you might find splitting out individual query objects worthwhile if you want to add things like authorization and logging, you could feed a query object into a pipeline.
I always use UoW with EF code first. I find it more performant and easier tot manage your contexts, to prevent memory leaking and such. You can find an example of my workaround on my github: http://www.github.com/stefchri in the RADAR project.
If you have any questions about it feel free to ask them.
Here's what I am trying to accomplish with Structuremap.
On each we request, database connection strings and web service urls used in our clients will vary based on some business logic. Currently, our sql and web service client implementations receive the configs in their constructors.
I wanted to use profiles, only to discover that it is not possible to use them per request.
In our team, we're having a debate over two solutions:
1- Pass a config factory into the registry that can resolve which configurations to use
when the container needs to instantiate something.
Problems I see is that we might have to use HttpContext.Items, as most of the app objects are not instantiated in structuremap and it seems hard to get the current request context from within the factory.
2- Instantiate containers for every different configurations and decide which container to use depending on the business logic.
Problems I see is the load time, the memory consumption and maybe the lifecycles of objects. So, I don't seem to find any real problem here, it just feels wrong to me to have multiple containers.
1- Do you see other problems?
2- Any better idea?
3- Which one would you choose?
Thank you
EDIT
and it seems hard to get the current request context from within the factory.
I don't mean HttpContext, I mean the request data. For this app, it is a wcf request object.
it seems hard to get the current request context from within the factory.
Not sure why it seems that way. Wouldnt the following do the trick?
ObjectFactory.Configure(config => {
config.For<HttpContextBase>()
.Use(() => { return new HttpContextWrapper(HttpContext.Current); });
config.For<Service>().Use<Service>();
});
var service = ObjectFactory.GetInstance<Service>();
public class ConfigurationFactory
{
public ConfigurationFactory(System.Web.HttpContextBase context)
{
}
}
public class Service
{
public Service(ConfigurationFactory Configuration)
{
}
}
I am building an ASP.NET 4.0 MVC 2 app with a generic repository based on this blog post.
I'm not sure how to deal with the lifetime of ObjectContext -- here is a typical method from my repository class:
public T GetSingle<T>(Func<T, bool> predicate) where T : class
{
using (MyDbEntities dbEntities = new MyDbEntities())
{
return dbEntities.CreateObjectSet<T>().Single(predicate);
}
}
MyDbEntities is the ObjectContext generated by Entity Framework 4.
Is it ok to call .CreateObjectSet() and create/dispose MyDbEntities per every HTTP request? If not, how can I preserve this object?
If another method returns an IEnumerable<MyObject> using similar code, will this cause undefined behavior if I try to perform CRUD operations outside the scope of that method?
Yes, it is ok to create a new object context on each request (and in turn a call to CreateObjectSet). In fact, it's preferred. And like any object that implements IDisposable, you should be a good citizen and dispose it (which you're code above is doing). Some people use IoC to control the lifetime of their object context scoped to the http request but either way, it's short lived.
For the second part of your question, I think you're asking if another method performs a CRUD operation with a different instance of the data context (let me know if I'm misinterpreting). If that's the case, you'll need to attach it to the new data context that will perform the actual database update. This is a fine thing to do. Also, acceptable would be the use the Unit of Work pattern as well.
Ive just started using EF4 with the repository pattern. Im having to call the dispose method after every use of context or wrap code arround in the using block. Can I use the ObjectContext without doing this in every method I write or is there a better way of handling this in the repository.
Also I dont want to pass the ObjectContext to the repository from the UI as well.
To do this as resource effectively as possible without dependency injection, I would suggest that you implement a private, lazy-loading property for the object context.
private ObjectContext _context;
private ObjectContext Context
{ get
{
return _context ?? (_context = new ObjectContext());
}
}
Next, make your repository implement IDisposable and take care of the object context in your dispose method:
public Repository : IDisposable
{
...
public void Dispose()
{
_context.Dispose();
}
}
Then, you just use the property in all your methods, and wrap usage of your repository in using statements.
To decrease traffic to the database, you could also factor out the saving to a separate method on the repository, which just forwards the call to the object context. That way you get more control of when data is saved in the UI layer, even though you don't control how. That means you could do
using (var repo = new Repository())
{
repo.AddSomeStuff("this", "is", true);
repo.ChangeSomethingElse("yes, please");
repo.Save();
}
and there would only be one call from EF to the database. On the other hand, if you do
using (var repo = new Repository())
{
repo.AddSomeStuff("this", "is", true);
repo.ChangeSomethingElse("yes, please");
}
nothing happens, which might be confusing.
The general pattern for using an object context is:
public BusinessObject GetSomething(){
using (MyObjectContext context = new MyObjectContext()){
//..do fun stuff
}
}
Which hopefully is the pattern you are using. Calling dispose seems a little overkill when you can just use a "using" statement.
Another option is if you are going to be doing multiple DB queries in a flow. I have seen a pattern where you can reuse the same context within the thread. People basically implement a Thread based singleton pattern and pass around the context. Advantages to this is not having to rebuild the context, as well as some in memory caching. Downside is you could run into concurrency issues. Someone updating something that you have cached internally in EF.
I am guessing the second case doesn't really apply because it sounds like you are writting a small app. (that statement was based on your comments about passing a context from UI...a statement which will scare any good code architect).
If you are interested in a thread based singleton. First learn about the Singleton pattern, and then check out this blog about "DataContext" threads. You will have to change the "DataContext" type to the ObjectContext class but it would work.
EDIT
I will say I overlooked an obvious solution and that would be the below ;). Just using a property based Object Context and playing your repository in a using statement. It would be the same as the using example above, but you would implement IDisoposable.