Does anyone know of a good (read: quick to code) method for converting DTOs to View Models or mapping DTO members to View Model members? Lately I've been finding myself writing many conversion and helper methods but this is a very arduous and tedious task. Moreover, it will often needs to be done twice (DTO -> View Model, View Model -> DTO).
Is there a methodology, technique, or technology which would allow me to do this more quickly and efficiently?
Have a look at Automapper. It is an open source project that addresses exactly the problem you are having.
As suggested by David, Automapper is highly flexible. If you have simple mapping need, check out the object mapping feature of Fasterflect, a library I co-authored. It offers very high performance (use CIL generation in the backend, instead of reflection) and is very easy to use.
I found Otis Mapper better than AutoMapper , which facilitates mapping a collection of entities to DTO collection .
Please find the link below.
Otis
Hope this helps.
Thanks ,
Vijay
I see automapper as the best solution for DTO Mapping
Related
I've been looking at the different approaches to solving the mass assignment issues with MVC as well as doing things the right way.
So far, the 2 approaches which I think are the best are below: (I have also looked at AutoMapper)
1: Value Injecter - This seems to do the job pretty well, but also relies on a third party library
2: Using the UpdateModel method and bind to a View Model interface which exposes a subset of the required properties in your domain model. http://www.codethinked.com/easy-and-safe-model-binding-in-aspnet-mvc
Before I jump in and code my whole application (without spending a week on each to find out which one I actually like) using one of the above practices, does anybody have real world experience of using these 2 methods and which one you would recommend?
in simple scenarios where you have only text fields matching strings/int properties anything will do just as well.
but when you have properties on the viewmodel that match objects in the model (FK in the DB) it gets a bit more complex, you might need to pull data from the DB for some individual props and map some property of that object to the ViewModel, stuff like that.
prodinner asp.net mvc demo application uses valueinjecter in Mapper classes, there's a pdf where this approach is explained, you can download it here: http://prodinner.codeplex.com/
General consensus from all the reading I've done on this topic is that if you're going from a Entity or Domain Model (from your database) to a View Model to show on the form feel free to use automation tools like AutoMapper or whatever your preferred tool is to automate it.
If you are however going from a Input or Form Model (the object populated via the automatic model binding) back into to your Entity or Domain Model, do not automate this. It's a slippery slope to navigate correctly and can result in your automation tool mapping over fields that were not intended/permitted. Everything I've read about this (and various implementations myself) suggest the best practice is to do this manually/explicitly. It's pretty straight forward and object initializers can make it very easy to read.
var person = new Person()
{
PersonId = model.PersonId,
FirstName = model.FirstName,
LastName= model.LastName
}
personService.UpdatePerson(person);
Something along that line.
Been working on a pet project on the side to learn asp.net mvc better. My question is about viewmodels in mvc. I understand the controller is supposed to handle the interaction between the view and the model. I feel like I keep having to create viewmodel classes to combine information from the models to pass to the view.
Is this bad practice? Should I be doing more of the logic elsewhere and cut down on the viewmodels?
At the moment I've almost got a viewmodel for just about every one of my main views. But I definitely don't want the view to access the model directly.
No, all your views should be strongly typed, so using for each view one viewmodel is best practice. Here is very nice article about viewmodels.
The more viewmodels you use the better. The viewmodels allow you to create a single object that can contain different types of data from your models. These are very useful when creating templates. Also, this is very useful when using JQuery and Ajax since its a nice way to pass data into your controller and then directly to the DOM. In my opinion, use as many viewmodel as you desire.
Another thing that you might consider is to try to have better design of your model. I personally try to build my model just like a sql database and follow the normalization forms. You should not have to create a new viewmodel for each view in addition to the models you already have. If you need to pass information to the view that is not part of the model you are using, use ViewData or ViewBag. These are passed as an object so you will have to cast them to the appropriate class.
Nothing bad in this. As much your viewmodel closer to view as better.
Model could not particullary match View, so you use ViewModel class for that.
Great answers here, and here is my view on why a lot of view models are not an issue.
Your ViewModels are a nice way of separating your pure Data Access Objects or even your Domain Objects from your presentation layer and provide a dumbed down version of those objects for your views to consume.
Your views are supposed to be dumb and for me personally, what I try to achieve is to massage my domain model into a ViewModel for my view to consume.
Using lot of viewmodels creates mess in your project. It is much better to just create a Tuple in the controller then pass it.
Lots of great posts out here on this topic and I've tried to read them all. I'm a long time n-tier developer but trying to swing into action with an MVC3/EF application. I've generated POCOs via the EF POCO generator(T4). I'm also binding ViewModels to my Views...no EF stuff in my Views. My question has to do with validation (U/I only). I like the idea of DataAnnotations and want to use them. However, to use them correctly I have to use them in my ViewModels. From the advice I see on this site and others, I'll have to replicate any properties from my POCOs into my view models and do my annotations there. To make this easier I've seen lots of suggestions to use AutoMapper to make this tedious mapping more bearable.
Do I pretty much have the right idea?
I'm also binding ViewModels to my Views...no EF stuff in my Views
Correct. Ideally, your POCO's should not be on your Views.
I like the idea of DataAnnotations and want to use them. However, to use them correctly I have to use them in my ViewModels
Correct. There shouldn't be any data annotations on your POCO's.
From the advice I see on this site and others, I'll have to replicate any properties from my POCOs into my view models and do my annotations there
Why? Are you always binding to all of the properties on your POCO's? Remember, the ViewModel is to serve the View only. So if you have a form to submit an order, the ViewModel should only contain what is required to persist that Order. A combination of AutoMapper and your custom code can then map that to your POCO.
To make this easier I've seen lots of suggestions to use AutoMapper to make this tedious mapping more bearable
#Craig is right, it has nothing to do with Data Annotations. AutoMapper maps your ViewModel to your domain models with a few lines of configuration.
AutoMapper is only about transformation from entity to view model and vice versa. It is just replacement of code like custom conversion operator between types. You will still have to create your view models and mark properties with correct data annotations.
I'm an ASP.NET MVC newbie, but have used many Model-View-Controller frameworks previously.
I recently came across the convention of gathering up the pieces of data that your particular view needs (indeed, it's assigned to the ViewData) into a new class called (NameOfView)ViewModel.
Gathering up this data so that it's associated with the functions provided by the View/Controller interaction strikes me as a helper struct, or even closure mechanism (in the 'encapsulates a collection of variables' sense).
So why is it called 'ViewModel', given that it's neither a View or Model?
Does anyone else find the name confusing?
EDIT: What's wrong with just putting properties onto the View so that the Controller can populate them (as in other MVC frameworks)?
In my reading on this topic I've come across a variety of arguments as to why a developer would or would not want to use a ViewModel. Some even argue that a ViewModel should never expose anything more than strings. At this point I am not that extreme in my thinking. I will agree however, that it is not a good idea to expose Domain/Core Objects to the view. After some first hand experience it feels cleaner to remove this dependency.
While I don't agree with everything below Daniel Root makes a pretty good case for a ViewModel:
Most MVC examples show directly using
a model class, such as a LINQ-to-SQL
or Entity Framework class. The Visual
Studio wiring for MVC even steers you
into this concept with it's default
"Add View" code-generation, which lets
you quickly gen up views based on a
single model class. However, in
real-world-apps you often need more
than just a single table's data to
build out a page. Some examples get
around this by stuffing secondary data
into ViewData, but a better way to do
this is to create a "roll-up" class to
contain properties for everything
your view will need. This has the
added benefits of being more
strongly-typed, supporting
intellisense, being testable, and
defining exactly what a view needs.
Jeff Handley gives a nice description of the ViewModel pattern which he argues can be used in conjunction with MVC.
Edit
I've recently brought my thinking in line with Jimmy Bogard's regarding view models. After a fair amount of pain with each implementation I've tried having one view model per view creates a much cleaner development experience.
The model is a view-agnostic representation of the data. The view model is a view-specific representation of the data: it's the model as it might appear from a given viewpoint.
Consider a model that consists of raw data points; a histogram view might then have a view model consisting of a set of buckets and totals drawn from that data.
Logically, it's a subset or transformation of the model - it could be generated on-demand with a view-specific function and the model as its only input.
Regarding properties on the view vs. a property bag or custom object... I'm sure someone has strong feelings on this, but personally I don't see the big difference. You're producing a view-specific representation of the model and passing it somehow; the exact mechanism doesn't seem all that important.
Re: why can't the controller populate properties on the view?
Because the view doesn't exist at the time the controller action is executing. The idea behind returning an ActionResult from your action is that something later in the processing pipeline will evaluate the result and determine the best course of action (perhaps rendering a view, or maybe selecting a view to match the request (like special views made for mobile devices)).
I did a view posts on selecting the right kind of model object here: Putting the M in MVC Part I, Part II, Part III.
And yes, the term "ViewModel" term is en vogue right now, but it is in the spirit the original MVC adopters had in mind.
This isn't actually an answer but I highly recommend you watch the MVC2 Basics video by Scott Hanselman. It explains everything, and even though I have done ASP.NET MVC before it made a lot of things clear for me.
Its here: http://channel9.msdn.com/Blogs/matthijs/ASPNET-MVC-2-Basics-Introduction-by-Scott-Hanselman
It's called that because it's a "Model made for a View". I understand why the choice of term is a bit confusing.
It's a helpful approach if you don't want all your data passed to the view as a big hash array. It gives you a strongly-typed class dedicated to the UI, which pollutes neither the core Model or the View. It also allows you to encapsulate UI logic -- views should be kept dumb.
How do most developers handle Typed Views in ASP.NET MVC when dealing with large applications? We are considering putting View-specific models in the Models folder, then putting all domain objects into a separate project. This way our Controllers can easily add the domain object to the typed view, without the domain object needing to be aware of the View layout itself.
For example, if we have an Employee object with:
Id
First Name
Last Name
Status
Then our Employee View might use a ViewEmployeeModel object with:
Employee object
List to populate Status drop-down
etc
Is this a sensible approach? Are there better ways to accomplish the same thing? It seems a little strange since I'd basically have two models (one for the view, one for the business objects), but isn't it better than using untyped views?
I do this almost as a rule, because:
It lets you design the app view-first instead of DB-first, which is nice when working with customer representatives.
Views typically have a much "flatter" object graph than, say, Entity Framework models. LINQ makes it easy to map these.
The views and the data model can evolve much more independently.
It's typically easier to model bind to a flat view model with, say, FK IDs than an entity model which expects fully materialized related objects.
You don't have to worry about accidentally exposing "secret" properties or whitelisting properties for updates.
Don't have the reputation to comment, but Craig is right. It's a variation of the Model-View-ViewModel pattern. There's a good article on it available at Los Techies.
The article also uses the AutoMapper code that mgroves pointed out so you should be able to kill two birds with one stone.
I think this is a pretty sensible approach. One thing that might help you out is AutoMapper.
Seems fine, you have the advantage that the model only contains information needed by the view and not lots of pesky business logic functions / values.