Using DTO to transfer data between service layer and UI layer - asp.net-mvc

I've been trying to figure this out for days but there seems to be very little info on this particular subject with ASP.NET MVC. I've been Googling around for days and haven't really been able to figure anything out about this particular issue.
I've got a 3 layer project. Business, DAL and UI/Web layer. In the DAL is dbcontext, repository and unit of work. In the business layer is a domain layer with all the interfaces and the EF models. In the business layer there is also a service layer with DTOs for the EF models and a generic repository service that accesses the repository. This picture should help explain it.
My problem is that i just can't seem to figure out how to use the DTOs to transfer data from the business layer.
I've created service classes for the DTOs. I've got a ImageDTO and model and same for image anchors. I've created a service class for each DTO. So i've got a image service and anchor service. These services inherit the repository service and at the moment implement their own services. But thats about as far as i have gotten. Since these services have constructors that receive a IUnitOfWork interface via IoC i've pretty much gotten stranded.
If i reference the service directly from the UI everything works as it should but i just can't get my mind around how to use DTOs to transmit data both from the service layer to the UI layer and the other way around.
My service layer:
Business/Services/DTOs
public class AnchorDto
{
public int Id { get; set; }
public int x1 { get; set; }
public int y1 { get; set; }
public int x2 { get; set; }
public int y2 { get; set; }
public string description { get; set; }
public int imageId { get; set; }
public int targetImageId { get; set; }
public AnchorDto(int Id, int x1, int y1, int x2, int y2, string description, int imageId, int targetImageId)
{
// Just mapping input to the DTO
}
}
public class ImageDto
{
public int Id { get; set; }
public string name { get; set; }
public string title { get; set; }
public string description { get; set; }
public virtual IList<AnchorDto> anchors { get; set; }
public ImageDto(int Id, string name, string title, string description, IList<AnchorDto> anchors )
{
// Just mapping input to DTO
}
}
Business/Services/Services
public class RepoService<TEntity> : IRepoService<TEntity> where TEntity : class
{
private IRepository<TEntity> repo;
public RepoService(IUnitOfWork repo)
{
this.repo = repo.GetRepository<TEntity>();
}
public IEnumerable<TEntity> Get(
Expression<Func<TEntity, bool>> filter = null,
Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
string includeProperties = "")
{
return repo.Get(filter, orderBy, includeProperties);
}
public TEntity GetByID(object id)
{
return repo.GetByID(id);
}
public void Insert(TEntity entity)
{
repo.Insert(entity);
}
public void Delete(object id)
{
repo.Delete(id);
}
public void Delete(TEntity entityToDelete)
{
repo.Delete(entityToDelete);
}
public void Update(TEntity entityToUpdate)
{
repo.Update(entityToUpdate);
}
}
The Image Service, the IImageService interface is currently empty until i figure out what i need to implement.
public class ImageService : RepoService<ImageModel>, IImageService
{
public ImageService(IUnitOfWork repo)
: base(repo)
{
}
}
At the moment my controllers aren't really working and aren't using the service layer so i decided not to include any of those. I plan to map the DTOs to ViewModels using auto mapper once i've sorted this issue out.
So now, please anyone knowledgeable enough to give me that idea I'm missing so that i can figure this out?

Your service should receive DTOs, map them to business entities and send them to the repository. It should also retrieve business entities from the repository, map them to DTOs and return the DTOs as reponses. So your business entities never get out from the business layer, only the DTOs do.
Then your UI\Weblayer should be unaware of the business entities. The web layer should only know about the DTOs. To enforce this rule is very important that your UI layer does not uses the service implementation classes (which should be private), just the interfaces. And the service interfaces shouldn´t depend on the business entities, just the DTOs.
So you need service interfaces based on DTOs, and your base service class needs another generic argument for the DTO. I like to have a base class for entities and DTOs so they can be declared as:
//Your UI\presentation layer will work with the interfaces (The inheriting ones)
//so it is very important that there is no dependency
//on the business entities in the interface, just on the DTOs!
protected interface IRepoService<TDto>
where TDto: DTOBase
{
//I'm just adding a couple of methods but you get the idea
TDto GetByID(object id);
void Update(TDto entityToUpdateDto)
}
//This is the interface that will be used by your UI layer
public IImageService: IRepoService<ImageDTO>
{
}
//This class and the ones inheriting should never be used by your
//presentation\UI layer because they depend on the business entities!
//(And it is a best practice to depend on interfaces, anyway)
protected abstract class RepoService<TEntity, TDto> : IRepoService<TDto>
where TEntity : EntityBase
where TDto: DTOBase
{
...
}
//This class should never be used by your service layer.
//Your UI layer should always use IImageService
//You could have a different namespace like Service.Implementation and make sure
//it is not included by your UI layer
public class ImageService : RepoService<ImageModel, ImageDto>, IImageService
{
...
}
You then need a way of adding the mapping between entities and DTO to that base service without actually implementing the mapping (as it depends on each concrete entity and DTO classes). You could declare abstract methods that perform the mapping and will need to be implemented on each specific service (like ImageService). The implemantion of the base RepoService would look like:
public TDto GetByID(object id)
{
//I'm writing it this way so its clear what the method is doing
var entity = repo.GetByID(id);
var dto = this.EntityToDto(entity);
return dto;
}
public void Update(TDto entityToUpdateDto)
{
var entity = this.DtoToEntity(entityToUpdateDto)
repo.Update(entity);
}
//These methods will need to be implemented by every service like ImageService
protected abstract TEntity DtoToEntity(TDto dto);
protected abstract TDto EntityToDto(TEntity entity);
Or you could declare mapping services, adding a dependency with an appropiated mapping service that should be provided by your IOC (This makes more sense if you need the same mapping on different services). The implementation of RepoService would look like:
private IRepository<TEntity> _repo;
private IDtoMappingService<TEntity, TDto> _mappingService;
public RepoService(IUnitOfWork repo, IDtoMappingService<TEntity, TDto> mapping)
{
_repo = repo.GetRepository<TEntity>();
_mappingService = mapping;
}
public TDto GetByID(object id)
{
//I'm writing it this way so its clear what the method is doing
var entity = repo.GetByID(id);
var dto = _mappingService.EntityToDto(entity);
return dto;
}
public void Update(TDto entityToUpdateDto)
{
var entity = _mappingService.DtoToEntity(entityToUpdateDto)
repo.Update(entity);
}
//You will need to create implementations of this interface for each
//TEntity-TDto combination
//Then include them in your dependency injection configuration
public interface IDtoMappingService<TEntity, TDto>
where TEntity : EntityBase
where TDto: DTOBase
{
public TEntity DtoToEntity(TDto dto);
public TDto EntityToDto(TEntity entity);
}
In both cases (abstract methods or mapping services), you can implement the mapping between the entities and DTOs manually or using a tool like Automapper. But you should be very careful when using the AutoMapper and entity framework, although that is another topic! (Google a bit about that and collect some information on the topic. As a first advice pay attention to the queries being executed against the database when loading data so you don´t load more than needed or send many queries. When saving data pay attention to your collections and relationships)
Long post maybe, but I hope it helps!

Related

IoC - Autofac and register multiple services with same generic Interface

I have a service layer with the following classes / intefaces (IServices is an empty interface):
public interface IForoChanService<T> : IService
{
T GetById(int id);
IQueryable SearchBy(Expression<Func<T, bool>> predicate);
IEnumerable<T> GetAll();
int Create(T entity);
void CreateMany(IEnumerable<T> entities);
void Delete(T entity);
void Delete(int id);
void DeleteMany(IEnumerable<T> entities);
void Update(T entity);
}
Then I have an abstract class implementing that signature generically:
public abstract class ForoChanServiceBase<T> : IForoChanService<T> where T : EntityBase
{
public T GetById(int id)
{
return ChanDbContext.Set<T>().Find(id);
}
//all the other methods as well
}
And finally the concrete classes:
public class CategoryService : ForoChanServiceBase<Category>
{
}
I am trying to use AutoFac to inject those services (many: category, client, etc) in the constructor: I have a base controller:
public abstract class ForoChanBaseController: Controller
{
protected ForoChanServiceBase<Post> PostService { get; private set; }
protected ForoChanServiceBase<Comment> CommentService { get; private set; }
protected ForoChanServiceBase<Category> CategoryService { get; private set; }
protected ForoChanBaseController()
{
}
protected ForoChanBaseController(
ForoChanServiceBase<Post> postService,
ForoChanServiceBase<Comment> commentService,
ForoChanServiceBase<Category> categoryService)
{
PostService = postService;
CommentService = commentService;
CategoryService = categoryService;
}
}
And I am setting autofac like this:
public static void ConfigureIoc()
{
var builder = new ContainerBuilder();
builder.RegisterType<CommentService>().As<ForoChanServiceBase<Comment>>().InstancePerRequest();
builder.RegisterType<CategoryService>().As<ForoChanServiceBase<Category>>().InstancePerRequest();
builder.RegisterType<PostService>().As<ForoChanServiceBase<Post>>().InstancePerRequest();
builder.Build();
}
The problem is that I am having is when in the controller I need to use any service method that guy (CategoryService) is null:
public ActionResult Create()
{
var p = new PostFormNewVm
{
Categories = CategoryService.GetAll().Select(c => new CategoryVm { Id = c.Id, Title = c.Title })
};
return View(p);
}
Besides this error do am I doing something wrong? I can't make it work.
I tried with the inteface as well.
Your ForoChanBaseController contains multiple constructors, which is an anti-pattern. Because of the existence of this default constructor, there is a derived class that uses this constructor instead of the overloaded one, which is causing the dependencies to be null.
Although this default ctor is the cause for you to post the question here, there are more -less obvious problems- with your design:
Although you can remove the default constructor, prevent having this base class at all. Bases classes are often big Single Responsibility Principle violations and are either used to stuff in cross-cutting concerns or other utility functions. By having this base class derived types are forced to require dependencies that they might not even use at all. This complicates your code and complicates testing.
Since you have the IForoChanService<T> interface, consumers should not depend on the ForoChanServiceBase base class. As a matter of fact, the same advise as before holds: this base class should probably not exist at all.
The IForoChanService<T> is big generic tool box of methods where consumers only use one or two of those methods at a time. This means you are violating the Interface Segregation Principle.
IForoChanService<T> implementations are likely to violate the Liskov Substitution Principle, since there will be implementations that don't allow entities to be deleted. This will cause call to Delete to fail with an exception, instead of the Delete to not exist for that entity.

ASP MVC EF6 Architecture

We have ASP MVC web project. After reading a lot of articles and discussions here in stackoverflow about the correct architechture we have decided to go with the following one, although there is not only one correct way of doing things this is the way we have decided, but we still have some doubts.
We are publishing this here not only to be helped but also to show what we have done in case it is helpful to somebody.
We are working in ASP .NET MVC project, EF6 Code first with MS SQL Server.
We have divided the project into 3 main layers that we have separate into 3 projects: model, service and web.
The model creates the entities and setup the DataContext for the database.
The service make the queries to the data base and transform those entities into DTOs to pass them to the web layer, so the web layer doesn't know anything about the database.
The web uses AutoFac for the DI (dependency Injection) to call the services we have in the service layer and obtain the DTOs to transform those DTOs into Model Views to use them in the Views.
After reading a lot of articles we decided not to implement a repository pattern and unit of work because, in summary, we have read the EF acts as a unit of work itself. So we are simplifying things a little here.
https://cockneycoder.wordpress.com/2013/04/07/why-entity-framework-renders-the-repository-pattern-obsolete/
This is the summary of our project. Now I'm going to go through every project to show the code. We are going to show only a couple of entities, but our project has more than 100 different entities.
MODEL
Data Context
public interface IMyContext
{
IDbSet<Language> Links { get; set; }
IDbSet<Resources> News { get; set; }
...
DbSet<TEntity> Set<TEntity>() where TEntity : class;
DbEntityEntry<TEntity> Entry<TEntity>(TEntity entity) where TEntity : class;
}
public class MyDataContext : DbContext, IMyContext
{
public MyDataContext() : base("connectionStringName")
{
}
public IDbSet<Language> Links { get; set; }
public IDbSet<Resources> News { get; set; }
...
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
modelBuilder.Properties<DateTime>().Configure(c => c.HasColumnType("datetime2"));
}
}
Here is how we declare the entities
public class Link
{
public int Id{ get; set; }
public string Title { get; set; }
public string Url { get; set; }
public bool Active { get; set; }
}
SERVICES
These are the generic classes we use for all the services.
As you see we use the DTOs to get data from the web layer. Also we connect to the database using Dbset = Context.Set()
public interface IService
{
}
public interface IEntityService<TDto> : IService where TDto : class
{
IEnumerable<TDto> GetAll();
void Create(TDto entity);
void Update(TDto entity);
void Delete(TDto entity);
void Add(TDto entity);
void Entry(TDto existingEntity, object updatedEntity);
void Save();
}
public abstract class EntityService<T, TDto> : IEntityService<TDto> where T : class where TDto : class
{
protected IClientContext Context;
protected IDbSet<T> Dbset;
protected EntityService(IClientContext context) { Context = context; Dbset = Context.Set<T>(); }
public virtual IEnumerable<TDto> GetAll()
{
return Mapper.Map<IEnumerable<TDto>>(Dbset.AsEnumerable());
}
public virtual void Create(TDto entity)
{
if (entity == null)
{
throw new ArgumentNullException(nameof(entity));
}
Dbset.Add(Mapper.Map<T>(entity));
Context.SaveChanges();
}
public virtual void Update(TDto entity)
{
if (entity == null) throw new ArgumentNullException(nameof(entity));
Context.Entry(entity).State = EntityState.Modified;
Context.SaveChanges();
}
public virtual void Delete(TDto entity)
{
if (entity == null) throw new ArgumentNullException(nameof(entity));
Dbset.Remove(Mapper.Map<T>(entity));
Context.SaveChanges();
}
public virtual void Add(TDto entity)
{
Dbset.Add(Mapper.Map<T>(entity));
}
public virtual void Entry(TDto existingEntity, object updatedEntity)
{
Context.Entry(existingEntity).CurrentValues.SetValues(updatedEntity);
}
public virtual void Save()
{
Context.SaveChanges();
}
}
We declare the DTOs in this project (this is a very simple example so we don't have to put all the code here):
public class LinkDto
{
public int Id { get; set; }
public string Title { get; set; }
public string Url { get; set; }
public bool Active { get; set; }
}
Then one of our services:
public interface ILinkService : IEntityService<LinkDto>
{
IPagedList<LinkDto> GetAllLinks(string searchTitle = "", bool searchActive = false, int pageNumber = 1, int pageSize = 10);
LinkDto FindById(int id);
LinkDto Test();
}
public class LinkService : EntityService<Link, LinkDto>, ILinkService
{
public LinkService(IClientContext context) : base(context) { Dbset = context.Set<Link>(); }
public virtual IPagedList<LinkDto> GetAllLinks(bool searchActive = false, int pageNumber = 1, int pageSize = 10)
{
var links = Dbset.Where(p => p.Active).ToPagedList(pageNumber, pageSize);
return links.ToMappedPagedList<Link, LinkDto>();
}
public virtual LinkDto FindById(int id)
{
var link = Dbset.FirstOrDefault(p => p.Id == id);
return Mapper.Map<LinkDto>(link);
}
public LinkDto Test()
{
var list = (from l in Context.Links
from o in Context.Other.Where(p => p.LinkId == l.Id)
select new OtherDto
{ l.Id, l.Title, l.Url, o.Other1... }).ToList();
return list;
}
}
As you see we use AutoMapper (version 5 which has changed a little) to transform from Entities to DTOs the data.
One of the doubts we have is if the use of "Dbset.Find" or "Dbset.FirstOrDefault" is correct and also if the use of "Context.Links" (for any entity).
WEB
FInally the web project where we receive the DTOs and transform those DTOs into ModelViews to show in our views.
We need to call, in the Global.asax Application_Start, AutoFac to do the DI so we can use our services.
protected void Application_Start()
{
...
Dependencies.RegisterDependencies();
AutoMapperBootstrapper.Configuration();
...
}
public class Dependencies
{
public static void RegisterDependencies()
{
var builder = new ContainerBuilder();
builder.RegisterControllers(typeof(MvcApplication).Assembly).PropertiesAutowired();
builder.RegisterModule(new ServiceModule());
builder.RegisterModule(new EfModule());
var container = builder.Build();
DependencyResolver.SetResolver(new AutofacDependencyResolver(container));
}
}
public class ServiceModule : Autofac.Module
{
protected override void Load(ContainerBuilder builder)
{
builder.RegisterAssemblyTypes(Assembly.Load("MyProject.Service")).Where(t => t.Name.EndsWith("Service")).AsImplementedInterfaces().InstancePerLifetimeScope();
}
}
public class EfModule : Autofac.Module
{
protected override void Load(ContainerBuilder builder)
{
builder.RegisterType(typeof(MyDataContext)).As(typeof(IMyContext)).InstancePerLifetimeScope();
}
}
As you see we also call AutoMapper to configure the different maps.
Then in our controllers we have this.
public class LinksController : Controller
{
private readonly ILinkService _linkService;
public LinksController(ILinkService linkService)
{
_linkService = linkService;
}
public ActionResult Index()
{
var links = _linkService.GetAllLinks();
return View(links.ToMappedPagedList<LinkDto, LinksListModelAdmin>());
}
...
public ActionResult Create(LinksEditModelAdmin insertedModel)
{
try
{
if (!ModelState.IsValid) return View("Create", insertedModel);
var insertedEntity = Mapper.Map<LinkDto>(insertedModel);
_linkService.Create(insertedEntity);
return RedirectToAction("Index");
}
catch (Exception ex)
{
throw ex;
}
}
}
Well, this is it...I hope this can be useful for somebody...and also I hope we can have a little help with the questions we have.
1) Although we are separating database from the web project we do need a reference in the web project to initialize the database and also to inject dependencies, is this correct?
2) Is it correct the approach we have done having our Entities->DTOs->ViewModels? It's a little more work but we have everything separated.
3) In the Service project, when we need to reference a different entity than the main one we are using in the service, is it correct to call Context.Entity?
For example, if we need to retrieve also data from the News entity in the links service, is it correct to call "Context.News.Where..."?
4) We do have a little problem with Automapper and EF proxy, because when we call "Dbset" to retrieve data, it gets a "Dynamic proxies" object so Automapper can't find the proper map so, in order to work, we have to set ProxyCreationEnabled = false in the DataContext definition. This way we can get an Entity in order to map it to the DTO. This disables LazyLoading, which we don't mind, but is this a correct approach or there is a better way to solve this?
Thanks in advance for your comments.
For Question no. 2
Entities->DTOs->ViewModels? is good approach
because you are doing the clean separation, the programmer can work together with ease.
The person who design ViewModels, Views and Controllers don't have to worry about the service layer or the DTO implementation because he will make the mapping when the others developpers finish their implementation.
For Question no. 4
When the flag ProxyCreationEnabled is set to false, the proxy instance will not be created with creating a new instance of an entity. This might not be a problem but we can create a proxy instance using the Create method of DbSet.
using (var Context = new MydbEntities())
{
var student = Context.StudentMasters.Create();
}
The Create method has an overloaded version that accepts a generic type. This can be used to create an instance of a derived type.
using (var Context = new MydbEntities())
{
var student = Context.StudentMasters.Create<Student>();
}
The Create method just creates the instance of the entity type if the proxy type for the entity would have no value (it is nothing to do with a proxy). The Create method does not add or attach the entity with the context object.
Also i read some where if you set ProxyCreationEnabled = false the child element will not loaded for some parent object unless Include method is called on parent object.

Multiple database contexts when using repository pattern

I am a bit lost right now... I've never seen this much divergent information regarding solution to the problem. But let us start from the beginning.
I am using ASP.NET MVC with Repositories injected to Controllers, thanks to the Ninject. I have 2 simple Entities: Admin with a list of created blog entries and Entries with one virtual Admin field.
Admin:
public class Admin
{
[Key, ScaffoldColumn(false)]
public int Id { get; set; }
[Required(ErrorMessage = "Zły login.")]
[StringLength(20), MinLength(3)]
[RegularExpression(#"^[a-zA-Z0-9]*$", ErrorMessage = "Special characters are not allowed.")]
public string Login { get; set; }
[Required(ErrorMessage = "Złe hasło.")]
[StringLength(20, MinimumLength = 3)]
[DataType(DataType.Password)]
[Display(Name = "Hasło")]
public string Password { get; set; }
public virtual List<Entry> CreatedEntries { get; set; } // napisane aktualności przez danego admina
}
Entry:
public class Entry
{
[Key, ScaffoldColumn(false)]
public int Id { get; set; }
[StringLength(200, MinimumLength = 2)]
[DataType(DataType.Text)]
[Display(Name = "Tytuł")]
public string Title { get; set; }
[Required, StringLength(2000), MinLength(3)]
[Display(Name = "Treść")]
[UIHint("tinymce_jquery_full"), AllowHtml]
public string Text { get; set; }
public virtual Admin Admin { get; set; }
}
You probably know where it is going, since this problem is... "classic" on stackoverflow.
In the Controller I want to bind one object to another:
entry.Admin = repAdmins.GetAdmin(User.Identity.Name);
repEntries.AddEntry(entry);
In the repository:
public void AddEntry(Entry entry)
{
db.Entries.Add(entry);
db.SaveChanges();
}
Of course I can't do that, because of famous "An entity object cannot be referenced by multiple instances of IEntityChangeTracker", which is a result of having separate database contexts in each repository.
When I was searching for a solution I already knew that probably the best way to solve it is to use one common context. And then I discovered Unit Of Work pattern. But here's when the real problems starts.
On many sites the solution to this is a bit different.
The repositories must have common generic interface (which I don't want to use, because I don't need to have each CRUD operation on each Entity, plus sometimes I need to have extra methods like "IfExists", etc.)
On few sites I've read that this whole abstraction is not needed, since abstraction is already provided with Entity Framework and UoW is implemented in DbContext (whatever that means)
The Unit Of Work pattern (at least from examples on the internet) seems to be a real pain for me...
I need some guidance... I learn ASP.NET MVC for only a year. For me it seems like it's a "triumph of form over content". Because... What I simply need is to bind one object to another. I'm starting to think that it was better when I simply had a context object in the Controller and I didn't need to build Eiffel Tower to achieve what's mentioned above :\ However I like idea of repositories...
I'll open by simply answering the question straight-out. Simply, your repository should take the context as a dependency (it should have a constructor that accepts a param of type DbContext). Your context should be managed by Ninject, and then injected into your repository and/or your controller. That way, everything always uses the same context. You should do all this in "request" scope, so that the context is specific to the current request.
That said, I'd like to hit some of your other points. First, a repository is just a method of access. It really shouldn't be dependent on the entity. It's okay to have methods that you don't intend to use on a particular entity: just don't use them. However, if you do want to enforce this, you can always use generic constraints and interfaces. For example, let's say you don't want update available on a particular entity. You could have interfaces like:
public interface ICreateable
{
}
public interface IUpdateable : ICreateable
{
}
Then, your entity that should not be updated will implement only ICreateable while other entities (which allow update) would implement IUpdateable (which by interface inheritance, also implement ICreateable). Finally, you would add constraints on your repository methods:
public void Create<TEntity>(TEntity entity)
where TEntity : class, ICreateable
public void Update<TEntity>(TEntity entity>)
where TEntity : class, IUpdateable
Since, the entity in question only implements ICreatable, it will not be eligible to be used as a type param to Update, so there's then no way to utilize that method.
Next, the advice to not use the repository/UoW patterns with Entity Framework is indeed because Entity Framework already implements these patterns. The repository pattern exists as a way to contain all the database querying logic (constructing SQL statements and such) in one place. That is the "abstraction" we're talking about here. In other words, instead of directly constructing SQL statements in your application code, that code is abstracted away into a repository. However, this is exactly what Entity Framework does, which is why you don't need to do it again. The Unit of Work pattern exists as a method to orchestrate the work of multiple repositories, allowing things like transactions. However, again, Entity Framework does all this.
The only reason to add any further abstraction is if you want to abstract the actual provider, i.e. Entity Framework itself. For example, you could have an interface like IRepository and then create implementations like EntityFrameworkRepository, NHibernateRepository, WebApiRepository, etc. Your application would only ever depend on IRepository, and you could then sub in different implementations as needed. If you're not going to do this, or you will always be using Entity Framework, then you might as well just use your context directly. Any further abstraction is just something else to maintain with no benefit at all to your application.
Finally, yes, the Unit of Work pattern is a real pain to everyone, not just you. Which is why I forgo it entirely. I use what I call a "truly generic repository", which utilizes generic methods and interfaces to handle any entity I want to throw at it. That means it acts not only as a repository but also a unit of work as well. You only need one instance per context and it's provider-agnostic. For more information check out the article I wrote on the subject over on my website.
The following example shows how to use the same context within multiple repositories. To simplify it, I did not use interfaces and nor did I use a container to inject dependencies.
Controller class:
public class HomeController : Controller
{
Context context;
AdminRepository adminRepository;
EntryRepository entryRepository;
public HomeController()
{
context = new Context();
adminRepository = new AdminRepository(context);
entryRepository = new EntryRepository(context);
}
// GET: Home
public ActionResult Index()
{
string login = "MyLogin";
Admin admin = adminRepository.GetAdmin(login);
Entry entry = new Entry() { Admin = admin};
entryRepository.AddEntry(entry);
return View(entry);
}
}
Repositories:
public class AdminRepository
{
Context context;
public AdminRepository(Context context)
{
this.context = context;
// This seeds the database
Admin admin = new Admin() { Login = "MyLogin" };
this.context.Admins.Add(admin);
this.context.SaveChanges();
}
public Admin GetAdmin(string login)
{
return context.Admins.Where(a => a.Login == login).FirstOrDefault();
}
}
public class EntryRepository
{
Context context;
public EntryRepository(Context context)
{
this.context = context;
}
public void AddEntry(Entry entry){
context.Entrys.Add(entry);
context.SaveChanges();
}
}
Context class:
public class Context : DbContext
{
public Context()
{
Database.SetInitializer<Context>(new DropCreateDatabaseAlways<Context>());
Database.Initialize(true);
}
public DbSet<Admin> Admins { get; set; }
public DbSet<Entry> Entrys { get; set; }
}
Modified Models:
public class Admin
{
public int Id { get; set; }
public string Login { get; set; }
}
public class Entry
{
public int Id { get; set; }
public virtual Admin Admin { get; set; }
}

Shall list members be injected into domain model?

Lately, I have invested my efforts into learning and understanding DI. Now that I'm growing more fluent with it, some other concerns come up.
Shall list members be injected into domain model?
In the famous example of Ninject, the idea as I see it is:
public class Warrior {
public Warrior(IWeapon weapon) { this.weapon = weapon; }
public void Attack() { weapon.Hit(); }
}
public Archer : Warrior {
// Here, the weapon would be bound to a bow.
public Archer(IWeapon weapon) : base(weapon) { }
}
public Ninja : Warrior {
// On the contrary, the weapon would here be bound to a katana.
public Ninja(IWeapon weapon) : base(weapon) { }
}
Hence contextual binding to define what weapon should be created depending on what the IWeapon is injected into.
I understand that injecting a DAO into my model would be implementing the Active Record design pattern, which is considered somehow an anti-pattern by some people. Others would prefer POCOs as domain objects, simple data representation, which is not following the rules of DDD.
Back to my concern, I would say that Warrior, Archer and Ninja are all part of my domain model.
Now, what if my model has an IList<T> instead of a IWeapon? Would DI be of any use, or would it become useless?
public class MyClass {
public MyClass(IList<MyOtherClass> myOtherClasses) {
MyOtherClassesA = myOtherClasses.OfType<MyOtherClassA>().ToList();
MyOtherClassesB = myOtherClasses.OfType<MyOtherClassB>().ToList();
}
public IList<MyOtherClassA> MyOtherClassesA { get; protected set; }
public IList<MyOtherClassB> MyOtherClassesB { get; protected set; }
}
Am I pushing it too far?
Am I missing something?
EDIT
No, do inject them! But don't inject one list of a base type, which you then split by derived types.
Let's put ourselves in the context of Scrum and a Sprint.
In a Sprint, the Development Team may have Bugs, Impediments, Tasks and UserStories.
All of these have a Title and a Description, plus some other properties specific to each type. Let's make an abstract class called Artifact (not ScrumArtifact).
Artifact
public abstract class Artifact {
public string Description { get; set; }
public string Title { get; set; }
}
Bug
public class Bug : Artifact {
public string Resolution { get; set; }
}
Impediment
public class Impediment : Artifact {
}
Task
public class Task : Artifact {
public float EstimatedTime { get; set; }
public float RealTime { get; set; }
}
UserStory
public class UserStory : Artifact {
public string AcceptanceCriteria { get; set; }
public int BusinessValue { get; set; }
public int Complexity { get; set; }
public IList<Impediment> Impediments { get; protected set; }
public IList<Task> Tasks { get; protected set; }
}
Here, I have a UserStory which "depends" on two lists: Impediments and Tasks.
So I should have the constructor of UserStory taking two lists as follows.
public UserStory(IList<Impediment> impediments, IList<Task> tasks) {
Impediments = impediments;
Tasks = tasks;
}
And my unit test:
[TestFixture]
public class UserStoryTests {
[Test]
public void ImpedimentsShouldBeInitializedByDefault() {
userStory.Impediments.Should().NotBeNull().And.BeOfType<IList<Impediment>>();
}
public void TasksShouldBeInitializedByDefault() {
userStory.Tasks.Should().NotBeNull().And.BeOfType<IList<Task>>();
}
[TestFixtureSetUp]
public void UserStorySetUp() {
impediments = new Mock<IList<Impediment>>();
tasks = new Mock<IList<Task>>();
userStory = new UserStory(impediments.Object, tasks.Object);
}
private Mock<IList<Impediment>> impediments;
private Mock<IList<Task>> tasks;
private UserStory userStory;
}
The problem comes with the Sprint. The Sprint rather require four lists, and I find it too much of objects to inject for clarity and readability. It is said, if I'm not mistaken, that a class with too much dependencies might break the Single Responsibility Principle. Though I'm not breaking the SRP even with the Sprint class, I feel quite uncomfortable with injecting four different lists. I thought I could use polymorphism to inject one list which would contain them all, since after all they are all basically Artifacts.
Perhaps shall I simply consider using the AbstractFactory pattern so that my four lists get initialized properly as expected, and I would only have to inject one single factory class which single responsibility consist of creating lists?
I think you misinterpreted the Ninject example a little bit. It doesn't involve different warrior classes, which are tied to a specific subtype of IWeapon. There's only a Samurai, who can use any type of IWeapon. So an Archer, who can only use a specific kind of weapon is not accounted for and wouldn't fit in well. Instead just inject a Bow into a Samurai.
Injecting lists is totally OK. Some DI containers even allow for autowiring lists. I.e. you can tell the container to inject all implementations of your interface found in a given assembly as a list.
But that only really works if you can treat all members in the same way, i.e. you don't have to differentiate by subtype. If you want to separate your warrior's melee weapons from his collection of bows, it's better to inject two different lists of two different types.
If you want to learn more about proper DI patterns, I can very much recommend Dependency Injection in .NET by Mark Seemann.

Where to bind DTO into domain model

I'm starting to use AutoMapper and some doubts arose.
Where is the correct way to map a dto into a domain model?
I'm doing this:
DTO:
public class PersonInsert
{
[Required]
public string Name { get; set; }
public string LastName { get; set; }
}
Action:
[HttpPost]
public ActionResult Insert(PersonInsert personInsert)
{
if (ModelState.IsValid)
{
new PersonService().Insert(personInsert);
return RedirectToAction("Insert");
}
return View("Insert");
}
Service:
public class PersonService
{
public int Insert(PersonInsert personInsert)
{
var person = Mapper.Map<PersonInsert, Person>(personInsert);
return new PersonRepository().Insert(person);
}
}
Repository:
public class PersonRepository
{
internal int Insert(Person person)
{
_db.Person.Add(person);
_db.SaveChanges();
return person.Id;
}
}
So, is this correct? should my service knows about domain? or should I make the bind in repository only? is correct to use [Required] in DTO?
I would almost never create an entity from a DTO - I explain why below. I would use a request object to allow a factory method to build the entity:
Request:
public class InsertPersonRequest
{
[Required]
public string Name { get; set; }
public string LastName { get; set; }
}
Action:
[HttpPost]
public ActionResult Insert(InsertPersonViewModel viewModel)
{
if (ModelState.IsValid)
{
InsertPersonRequest request = InsertPersonViewModelMapper.CreateRequestFrom(viewModel);
new PersonService().Insert(request );
return RedirectToAction("Insert");
}
return View("Insert");
}
Service:
public class PersonService
{
public int Insert(InsertPersonRequest request)
{
var person = Person.Create(request.name, request.LastName);
return new PersonRepository().Insert(person);
}
}
Repository stays the same.
This way all logic for creating the Person are located in the Factory method of the person, and so business logic is encapsulated in the domain - derived fields, default fields etc.
The problem with what you are doing is that the DTO has to be created in the UI, then all fields are mapped to the entity - this is a sure fire way for business logic to seep into the service layer, UI, or anywhere it is not supposed to be.
PLease read that again - This is a very serious mistake I see made time and time again.
I would however, use AutoMapper in the service layer to return a DTO:
Service:
public class PersonService
{
public PersonDto GetById(intid)
{
var person = new PersonRepository().GetById(id);
var personDto = Mapper.Map<Person, PersonDto>(person);
return personDto
}
}
Is this correct?
I personally don't see anything wrong with having your service do the mapping
Is it correct to use [Required] in DTO
No, DTOs should have no business logic whatsoever. They should be used purely for transmitting data across different tiers/layers of your application.
DataAnnotations are typically used on ViewModels for client/server side validation, therefore, I would add another separation into your model and introduce a ViewModel for your Insert action e.g.
public class PersonViewModel
{
[Required]
public string Name { get; set; }
public string LastName { get; set; }
}
public class PersonDto
{
public string Name { get; set; }
public string LastName { get; set; }
}
Action:
[HttpPost]
public ActionResult Insert(PersonViewModel personViewModel)
{
if (ModelState.IsValid)
{
var personDto = Mapper.Map<PersonViewModel, PersonDto>(personViewModel);
new PersonService().Insert(personDto);
...
}
...
}
}
Service:
public class PersonService
{
public int Insert(PersonDto personDto)
{
var person = Mapper.Map<PersonDto, Person>(personDto);
return new PersonRepository().Insert(person);
}
}
It may seem overkill in this scenario (considering the only difference is the [Required] attribute). However, in a typical MVC application you would want to ensure a clean separation between your ViewModels and your business models.
I would say that your PersonService could be seen as part of the domain layer (or Application layer directly above the domain) of your architecture and the controller and DTO is in a layer above that. That means you shouldn't have a reference to the DTO in your PersonService signatures and instead use the domain Person class here. So the Mapping code should go into the Controller. This ensures that your domain logic is not affected by changes to the webservice contract which could really be just one way to use your PersonService.
I would also introduce an interface for your repository which is injected into your PersonService because the PersonService again shouldn't need to know about concrete data access implementations.
As for the [Required] attribute, I don't see a problem with having this on the DTO because it just states the data contract of your webservice method. Anybody calling your webservice should adhere to this data contract. Of course this requirement will typically also be reflected somewhere in your domain code, maybe by throwing an exception etc.
In ASP.NET MVC the typical use of DTO is being part of something called viewmodel. Viewmodel is a class that will combine one to several DTOs into one class tailored for view presentation and posting values back to server.
What you doing is correct, no issues with that, but data annotations should reside on view models, rather than DTOs. Unless you call your DTO a view model, then its fine.
Please read the following posting about model (Domain Model) vs ViewModel in ASP.NET MVC world:
ASP.NET MVC Model vs ViewModel
Confused with Model vs ViewModel
Hope this helps
I think it is fine to have annotations on the DTOs, such as [Required], MaxLength, Range etc.
Your DTO can come in from any (possibly untrusted) source (Not just your website, but from another endpoint, WCF service, etc). All requests will be funneled to your Service/Business Layers, so you will need to validate the input before performing your business logic (simple guard checks). Having the annotations on the DTO simply describe the needed input to perform the task at hand. Passing an object with annotations is not peforming validation.
However, I believe you should be validating the DTO information is correct in the service/business layer (and annotations are a nice way to check this).
Just my thoughts on the situation :)

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