I'm currently developing a multi-tiered application, using MVC3 and Spring.NET all of which is going well. I have one question with regards to razor, and assigning a model to it. For instance, my definition for say, Member is in the Domain layer, is it acceptable to decorate the fields with Data Annotations here, and use this directly in the views? It seems to go against the separation of concerns to a certain degree.
That being the case, what would be the best way to do it? Redefine the required classes in the Model, and use them there?
Any suggestions/recommendations would be greatly received.
R.
A standard approach here is to use ViewModels and to annotate these with the validation attributes that apply to the presentation layer. With this approach, you would map the domain object properties to properties on the ViewModel; a library like AutoMapper can really help to reduce duplicating code all over the place in this regard.
Sometimes you may find that all your ViewModel does is simply wrap the domain object. In these instances I still think that this is a good thing to do as it allows you to add any presentation functionality to the ViewModel that is specific to the model and context, an option you don't have if you map the domain object straight to the view.
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I am looking to implement the Onion Architecture into our ASP.NET MVC application. I understand the need to separate View Models from Domain Entities, however I am finding myself writing redundant code. There is redundant code because my view models and domain entities look exactly the same with the exception that my view models have the [Serializable] data annotation. I need these models serializable because I am using ASP.NET Session State in which the State Server needs objects to be serializable.
I personally feel the domain entities should NOT be serializable because it would then become dependent on a particular technology. However, how can I avoid redundant code?
I should add that my service methods are dependent on these serializable data models.
I would avoid annotating my domain objects with anything persistence or non-domain related. This way, my Domain project wouldn't depend on another layer and I won't have it cluttered with things that aren't relevant to the Domain. While we need to bend the rules, I prefer bending them in a way not involving dependency on a persistence detail.
The point is to keep the layers focused on their purpose because it's very easy to mix'em up and create (in time) the big ball of mud.
In your case, I have the feeling you don't really have a rich domain or it's improperly modeled. It seems you only have data structures and your needs are CRUDy.
If you are certain the app won't evolve to become more complex i.e it will be just data structure manipulations then you can have one model to use them for all the purposes. Basically you can cut corners and use the 'business' model for everything. No need for abstractions and other stuff.
But if you think the app will evolve or they are or will be business rules and processes i.e you'll need to model behaviour as perceived by the business, then it's best to keep things very decoupled, even if at this stage they seem to be identical.
To make it easier, for your view model you can define one (with copy paste) and use automapper to map the business object to the view model one. Other approach maybe that your query service/repository/object could return directly that view model (map the query result to the view model)
Viewmodels can contain domain entities/models. My domain entities are partial classes and all (eventually) inherit from a base entity which is serialized. Since I use my domain models within some of my viewmodels, I use data annotations on the domain models as well. Your domain model library should not depend on/reference anything else (domain driven).
I wouldn't call [Serializable] a data annotation per se, since it's part of the core .Net platform (mscorlib.dll). Data Annotations refers to specific attributes used to perform data validation and other operations in ASP.Net or Entity Framework.
Should an Entity be [Serializable] ? Probably not, but I don't think this attribute is as "adulterating" to your domain layer as other attributes that come from external, web- or persistence-oriented libraries. It doesn't tie you to a particular third-party framework.
The whole "redundant code" issue depends IMO on the type of system you're building. In a genuine DDD application, duplication between Domain entities and View Models will probably not be all that blatant, and the benefits of a separate presentation model will typically outweigh the costs. A good article on that subject : Is Layering Worth The Mapping ?
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Where to write Database and Business logic in MVC?
I have just started with MVC3 pattern. How do we do data access in MVC3? Do we make the 'MODEL' as Data Access Layer or Do we add another 'DAL' layer and call it from 'MODEL' Layer?
Your model should be independent of data-access stuff, which will allow you to change your DAL strategy in the future.
You should be feeding the model from the DAL, but the model shouldn't know how it is being constructed, and certainly shouldn't have any database-specific code in it.
If you take the approach I suggest, look at AutoMapper - a very useful tool for mapping data between DAL and model classes.
When I was working with my last MVC3 project, my understanding from the various samples (such as GeekDinner) was that the Entity Framework serves as the Data Access Layer.
Your Model can be a directly mapped data access object, but don't necessarily have to be. They could just as well be proxies through to your backend DAL which is always going to be the better option depending on your requirements and longevity of the project.
The way I tend to handle it for larger projects is to have a separate namespace called Project.Entities which contains my Entity Framework data models. My Project.Models would contain models which use the Entities as a backing store for their data, and provide common methods (Where necessary) to manipulate that data. It may not be the best way to do it, but provides the most flexibility, and sticks to keeping data models separate from the backing store which allows more abstraction. For example, you can always switch out the underlying data layer to in-memory storage, another DAL than Entity Framework or whatever else.
For smaller/temporary/test projects, my Entity Framework data models will be straight in Project.Models and used directly as it's quicker and doesn't require so much thought.
No, model is not data access. Model is a buch of classes to hold data, and it generally does not contain code other than, possibly, to verify the assigned values are permitted.
You access data from controllers. In which way you do that is completely up to you and MVC is not concerned.
Model is your view model, not your domain model.
If you want to do DAL activity, I would tend to wrap it in repository/service that can be injected into your controllers.
This stops your controllers getting bloated and also allows you to mock your DAL layer for unit testing the controllers.
I've done a couple of projects in ASP.NET MVC and there is a topic that I haven't really seen covered anywhere. I wanted to get some other peoples' opinions on this.
What are some best practices for designing models? I've taken two approaches in the past: Should models represent distinct entities, or should you have domain specific (sub-domain specific? view specific?) models? The difference really being models representing distinct entities are used in more than one view where as the domain specific models are tied to specific views.
Consider the following: I have a User entity in my application. Should I have a single UserModel that I use in the Register view, the Show view, the Index view, etc., or would it be preferred to have a RegisterUserModel, a ShowUserModel, a ListUserModel, etc.?
I've used both patterns before. The up side of the domain specific models is that any validation logic applied via attributes can be different between views. The down side is you violate DRY and your models get pretty hairy -- even if you separate them in to namespaces. Conversely, using the single model-to-entity pattern leads to overly generic validation data (usually with regard to error messages) but you have a nice, tight model layer and converting between models and entities is a lot easier (less code).
What approach does SO prefer? Or is there an approach that I'm not even considering?
I like to create my data models and then create specific view models as I need them.
The Case for ViewModel
The ViewModel Pattern
When I think of domain models, I think about business logic as well. I try to keep the M in MVC to refer to the models that assist in the presentation aspect of the application, and not the entities (domain objects) that represent my real-world objects.
Model and View shuld be a pair. Building huge Model classes and huge Views is not good idea. In my opinion in your view-Model you should represent only needed part of your business logic. For example. When you'r creating Registration form make your Model and View that simple as it can be possible - Create RegisterUserModel.cs and RegisterUserView.aspx. Do not pass there whole User object. Make it light, don't break Single Responibility Principle.
I am just figuring out best practice with MVC now I have a project where we have chosen to use it in anger.
My question is.
If creating a list view which is bound to an IEnumerable is this bad practise?
Would it be better to seperate the code generated by the WCF Service reference into a datastructure which essentially holds the same data but abstracts further from the service, meaning that the UI is totally unaware of the service implementation beneath.
or do people just bind to the proxy object types and have done with it ?
My personal feeling is to create an abstraction by creating a model and placing the Collection in that and referring to the collection in the UI code from the model.
but this seems to violate the DRY principle with respect to proxies.
Well, the best practice is to use a View Model which is populated from the Model. In many cases they could be the same because the view shows all the properties returned by the service, but another view could show only a subset of them. That's why having a view model is considered a good practice. This view model can also contain some calculated properties that are specific to the view. To further simplify the mapping between those objects you could use AutoMapper. There's also a nice article you may take a look at explaining the concept of view models.
I have an ASP.NET app with a three layer architecture:
Presentation layer: ASP.NET
Bussiness Layer: C# library.
Data Access Layer: C# library with
ADO.Net Entity Framework objects.
Some methods on Bussiness layer would return ADO.NET entity objects but, data access layer is not visible at Presentation layer I can't do that.
My question is: On a design view, Is it correct to expose Entity Objects in the Presentation Layer? I think I only have to link Data Layer library with ASP.NET app.
Thank you!
It's absolutely desirable to have your entity objects available for use and consumption in your presentation tier. That's what all the work is for.
Binding collection of objects to a grid/listview/dropdown
Splashing a single object (i.e. customer) onto a form for read/update/delete
This makes your life easier by far. Otherwise you'd have to pass string after int after double after string between your presentation and business layers.
These may be Entity objects or even your own POCO objects that were hydrated from the Entity objects.
I would even go so far as to say that your Entites should be in their own assembly separate from the DAL.
I suggest that you look into the concepts of View objects...or Data Transfer Objects (DTO). You might consider using a tool like AutoMapper or similar which will create a view specific domain object out of your entities. In general you may have screens that need an entity present to perform its work. But more often than not you will need to pass several different entities. In this case you are better off creating one DTO that contains all of these entities. By doing this you are adding a layer of separation between your presentation layer and your business layer. Often times your entities have more power than you might want to expose to your presentation layer. And...vice versa. Frequently you may need to get some UI messages out to the presentation layer based on some validation flagged in your business layer. Rather than make your ui more complex than it needs to be (by passing in your full entities) you can only pass in what the UI needs in the form of the DTO. Also, there is never a need for your business objects to care about anything specific to the presentation layer. I suggest that you not databind directly to anything as far back as the data access layer. Technically your presentation layer should know as little as possible about your business layer. In the case of MVP or MVC this is very easy to achieve by disconnecting the front end and the back end by way of this additional separation!
I think no, it is not, the best way to do that is to separate data classes from behavior, and reference only data classes in presentation level.The good approach I think to use WCF see this link
See Supervising Controller and Passive View
If you pass the Entity, you are essentially Supervising controller. Otherwise you are Passive View.
Supervising controller is less work, but less testable. Supervising Controller also says databinding is OK.
Passive view is testable but a LOT more work. No databinding. Lots of properties.
Typically I stick with Supervising Controller. You typically don't need that level of testability and it isn't worth the extra trouble.