I am pretty new to MVC and I am looking for a way to design my models.
I have the MVC web site project and another class library that takes care of data access and constructing the business objects.
If I have in that assembly a class named Project that is a business object and I need to display all projects in a view ... should I make another model class Project? In this case the classes will be identical.
Do I gain something from doing a new model class?
I don't like having in views references to objects from another dll ... but i don't like duplicating the code neither.
Did you encounter the same problem?
I usually use a combination of existing and custom classes for models, depending on how closely the views map to the actual classes in the datastore. For pure crud pages, using the data class as the model is perfect. In real world use though you usually end up needing a few other bits of data. I find the easiest way to combine them is something like
// the class from the data store
public class MyDataObject {
public string Property1 {get;set;}
public string Property2 {get;set;}
}
// model class in the MVC Models folder
public class MyDataObjectModel {
public MyDataObject MyDataObject {get;set;}
// list of values to populate a dropdown for Property2
public List<string> Property2Values {get;set;}
// related value fetched from a different data store
public string Property3 {get;set;}
}
I also have quite a few model classes that are just a set of form fields - basically corresponding to action parameters from a particular form rather than anything that actually ends up in the database.
If it is exactly the same project then obviously don't need to duplicate the Project class, just use it as is in the view. But in real life often views have specific requirements and it it a good practice to define view model classes in your MVC application. The controller will then map between the model class and the view model to be passed to the view.
You will likely find differing opinions on this. I will give you mine:
I tend to, by default, reuse the object. If the needs of the view change and it no longer needs most/all of the data in the business object, then I'll create a separate view. I would never change the business object to suit the view itself.
If you need most/all of the information in the business object, and need additional data, then I would create a view that holds a reference to the business object and also has properties for the additional data points you need.
One benefit of reusing the business object is that, depending on the data access technology you are using, you can get reuse out of validation. For isntance, ASP.NET MVC 3 coupled with Entity Framework is nice as they both use the attributes in the System.ComponentModel namespace for validation.
That depends on what you mean by model. In the architecture I typically use, I have my Domain model, which is a collection of classes in a separate class library. I use DataAnnotations and built in validation to automatically validate my model when saving.
Then there is the View model, which I place in my MVC project. View models only have the information relevant to the view. I use data annotations here as well since MVC will automatically use them for my validation.
The reason for splitting the model this way is that you don't always use every piece of your domain model in a view. That means you either have to rebuild the data on the backend or you have to stash it in hidden fields. Neither is something I like,.
Related
I've split my project into (as of this time) 4 layers:
Application (ASP.NET MVC project)
Domain/Model (contains only models with no logic in them at all)
BusinessLogic (right now only "wraps" the repositories)
DAL (Entity Framework, but should be interchangeable)
The MVC Controllers use the business logic "services" to talk to the database through whatever lies beneath the business logic layer, and the controller should not need to tell anyone that "I want this Student, and I also want all his Courses" - this implies that lazy loading should be used.
The thing is, if I just "call through" and return the result to whoever calls the controller action, I can't really control what gets loaded unless I explicitly access the properties on the model to trigger the loading of the graph.
I'd like to use AutoMapper to map from my model to a Dto (one for each model, which defines what gets returned).
Say I have a model like this:
public class Student
{
public string Name {get;set;}
public int Age {get;set;}
public ICollection<Course> Courses {get;set;}
}
And a dto like this:
public class StudentDto
{
public string Name {get;set;}
public ICollection<Course> Courses {get;set;}
}
When AutoMapper does the mapping, it doesen't appear to map the Courses, which is my problem.
Should I be eager-loading at the repository layer instead?
As you have in the Student and StudentDto Automapper should map object graph correctly to the dto. This will work only if lazy loading enabled otherwise you may need to use eager loading.
I think the best way to choose what method to use is to test the performance of both method which will depend on several factors like your data model in the db and the delay between the sql server and your application etc.. .
Edit.. How to choose the best method
How to choose the best method
You need to consider three things,
How many connections that you are going to make with the database. If you are using lazy loading there will be a database call for all the reference points of a navigation properties if referred navigation property is not in the context.
How much data that you are going to retrieve from databaseIf you choose to load all the data in initial query with differed loading it will be too slow when you have huge amount of data to retrieve.
Complexity of the query . When you are using lazy loading the queries will be simple because all the data is not loaded in the initial query. If you use immediate loading it will make quires will be more complex with query paths
read more here
I am new to MVC and am having a conceptual problem with state and object persistence and hope someone can put my thoughts in order.
I have a remote webservice which provides methods to manage orders. An order consists of a header and Lines as you would expect. Lines can have additional requirements.
I have my domain objects created (using xsd2code from the webservice schema), the webservice calls and object serialization all working fine. I've build the DAL/BLL layers and it's all working - tested using a WinForms testbed app front-end.
I have view model objects mapped from the domain objects using Automapper. As the order is returned from a single webservice method complete with lines etc I have an OrderViewModel as follows
public class OrderViewModel
{
public OrderHeaderViewModel OrderHeader { set; get; }
public List<OrderLineViewModel> OrderLines { set; get; }
public List<OrderLineAdditionalViewModel> OrderLineAdditional { set; get; }
public List<OrderJustificationViewModel> OrderJustifications { set; get; }
}
Firstly I'm wondering if I should dispense with the OrderViewModel as if I pass this as a model to a view I'm passing far more data than I need. Views only need OrderHeader or OrderLines etc - not the entire order.
Now my conceptual problem is in the controllers and the views and object persistence.
My Order controller has a Detail Action which performs the load of the order from the webservice and maps the Domain object to the OrderViewModel object.
public ActionResult Details(string orderNumber)
{
OrderViewModel viewModel = new OrderViewModel();
var order = WebServiceAccess.LoadOrderByOrderNumber(orderNumber,"OBOS_WS");
viewModel = AutoMapper.Mapper.Map<BusinessEntities.Order, ViewModels.OrderViewModel>(order);
return View(viewModel);
}
But the Order/Details.cshtml just has the page layout and a call to two partial pages for the header and the lines (I swap the Headerview for a HeaderEdit using Ajax, same for the LinesView)
#{ Html.RenderPartial("DetailsHeaderViewPartial", Model);}
#{ Html.RenderPartial("DetailsLinesViewPartial", Model);}
At the moment I'm passing the model into the main Details container page, then into the RenderPartials, However I don't think that the model should be passed to the main Detail page, as it doesn't need it - the model is only needed in the DetailsHeaderViewPartial, DetailsLinesViewPartial so I'd be better off using #RenderAction here instead and passing the model into the Header/Lines views instead.
However, The Order is retrieved from the webservice in the ActionResult Details() how can I make the retrieved OrderViewModel object available in the ActionResult HeaderDetails() / LineDetails() methods of the controller to pass as the model in return PartialView(...,model) ?
Should I use a User Session to store the Order ViewModel so it can be used across actions in the controller.
Moving on from this stage the user will be able to maintain the order (add/remove lines - edit the header etc). As the webservice call to save the order could take a few seconds to complete I'd rather only call the save method when the user has finished with the order. I therefore would like to persist the in-progress order locally somewhere whilst it's being worked on. User session ?
Many thanks for any advice. Once I've got my head around state management for the ViewModels I'll be able to stop reading a million Blog posts and actually write this thing !
You actually have a few questions here so I will try to address them all the best I can.
1) Dispensing with the view model : I would say no. The view model represents the data that you need in order to populate your view. It seems like you are using the view model as an identical container to the domain model object. So you are asking if you should dispense with it and just pass the domain model to the view while your original concern is that you are passing along more data then you really need as is?
Rather then dispensing with the view model, I would revisit your properties on your view model. Only use properties that you need and create the mapping logic (either with automapper or on your own) for taking the complex domain object and populating the properties on the view model.
summation: build the view model to be only things that the view needs and write mapping logic to populate that view model.
2) This is just a statement of best practice before I breakdown your specific scenario.
You describe your architecture as having a BLL and DAL. If that is the case then you should not be persisting any objects from your controller. The controller should not have any knowledge of the database even existing and the objects used in the controller should have no idea of how to persist themselves. The objects that are going between your controller and the web service should strictly be Data Transfer Objects (DTO's). If you are unfamiliar with what constitutes a DTO then I highly suggest that you do some research and try to build them into your solution. It will help you conceptually see the difference between view model objects, domain objects and data transfer objects.
3) I would not try to store an order object in the session. I would re-analyze how you are breaking up the partial views within the view so that you can call actions with the ordersviewmodel being the parameter in a way that you need. It sounds like you are needlessly breaking up views into partial views.
4) You should not be concerned with state management for the view model object. Your view (which can be comprised of many partial views) is filled based on properties provided by the view model. The user can make changes using the UI you have developed. Since you express the desire to only save once they are finished making all changes to optimize calls to the web service, you just need to repopulate the fields of the view model upon clicking submit. Now you have a "state" for orderviewmodel that represents the users changes. You can send this object to the web service after converting back to a DTO (if you do what I said above) or by mapping it to the domain object.
1 final note. You are using automapper to map your domain to the view model. I am assuming that your view model is too complex and includes things that you don't need because you built your view model to emulate the domain object so that automapper could map by naming convention. Automapper has an api for doing complex (custom) mappings that fall outside of standard same name properties. Don't let automapper constrain you to building your view models a certain way.
Hope this helps
I am working on a fairly large MVC 3 application, and I'm running into an issue that doesn't smell quite right to me. This question takes a little set up to understand, so here are the premises that I'm currently operating on:
Views should be strongly typed (ViewBag/ViewData should be avoided)
Because the views are strongly typed, view model objects should be created that encapsulate all the data the view needs to display
When we have a need for drop down menus we should have two properties:
A property in the model that stores the selected value of the drop down
A SelectList property in the view model that represents the items in the drop down
The view itself always uses the #Html.DropDownListFor() helper method
We are using Entity Framework 4, and letting it generate entity classes from our already designed database
To avoid duplication and take advantage of LINQ, we are not creating our own separate business/model classes but adding to the partial classes generated by the entity framework
These partial classes that we write are located in the business layer to make everything compile correctly
Most model classes have a shared editor template that can be used in multiple views
Here's where the trouble comes in. The shared editor template's model type is set to the model class. This means that the partial view that makes up the editor template does not have access to the containing view model object where the list of drop down items is stored.
I was able to "solve" this by adding a SelectList property directly to the model class in the business layer instead of keeping it in the view model. But the SelectList class is specific to MVC, which in turn means that my business layer has a dependcy on MVC. That doesn't seem right to me because the BL should be agnostic to the UI.
Has anyone else run into this issue? How should I solve this? It's also possible that one of my premises are wrong.
Everything seems very nice and good design up until this point (which is not surprising as it is that point that is causing you headaches :-)):
Most model classes have a shared editor template that can be used in multiple views
It's view models that should have editor templates and not EF models. And because view models are specific to the requirements of the view you are free to put whatever information you need into them, like in this case the SelectList. So don't simply define a root view model that has your EF models as properties (that's not a view model). Define a view model that is designed to meet the requirements of the particular view. Don't put a single EF class in your view model hierarchy and you will see how much simpler your life will be :-)
And don't worry if you have duplicate properties in your view models. That's what those classes are designed for. Also AutoMapper could greatly simplify the mapping between your models and view models.
You have 2 main solution IMHO:
1. Generate DTOs / Models for your business logic entities
You can use AutoMapper to minimize the copying code.
You will achieve a nice separation between your view and business logic.
This however may be time-consuming for your large application.
2. Use extension methods
Instead of declaring a SelectList property in EF entity partial class and polluting your business logic with view-related code create an extention methods for your EF entites in Web project. You can than move your view-related code to web project from BL and keep type-safety.
Example:
Business Logic assembly
// This is EF entity
public partial class FooTable
{
public long Id { get; set; }
public string Name { get; set; }
}
Web assembly
public static class FooTableExtensions
{
public static SelectList GetSelectList(this IEnumerable<FooTable> fooTables)
{
return new SelectList(); // Create your select list from FooTables here.
}
}
Well, we ended up taking the simple way out. In the business layer we just changed the type to plain old Object. I figured that, regardless of the presentation layer, it will need some sort of list to contain the options available.
I know this isn't super clean as per #Darin and #Jakub, but I don't see our end result being any different this way except that we've avoided having to write and/or set up a whole bunch of mappings between objects.
I have been learning ASP.NET MVC for a few months. I have learned about views and controllers and models and stuff. To design a view, we always need a model.
Usually a model is a just a class which we fill with data and pass to a view. I have a question here: Should a model itself do some calculation, or should it just be dumb?
For example, I have a site where I load Books by Users. My model class is as follows:
public class FormViewModel
{
public User MyUser {get; set;}
public Books UserBooks {get; set;}
//Constructor here.
public FormViewModel(User _user, Books _userBooks)
{
this.MyUser=_user;
this.UserBooks=_userBooks;
}
}
This class doesn’t do anything — it’s just a template. Now if I modify the code as follows:
public class FormViewModel
{
public User MyUser {get; set;}
public Books UserBooks {get; set;}
//Constructor here.
public FormViewModel(User _user)
{
this.MyUser=_user;
this.UserBooks=_user.GetBooks();
}
}
which Books are collected depends on which User has been selected. Now it’s much easier to work with.
I just want to know what is a good approach according to MVC patterns and practices.
You want to separate all of your business logic, and data validation into the model. Usually that includes "grouping" datasets and such or filtering data by some criteria.
You want to separate all calls to these methods of the model in the controller, who's responsibility is to retrieve and send data to and from the model. The controller then passes the applicable data set into the view.
The Helpers are logic that is used by the view to do presentation logic (not business logic or validation) such as printing menus and such.
The View is where you will use the Helpers (or not, they are not required to use MVC properly but they do "help" :p) to write HTML, CSS and JS to the browser. You may also separate commonly used view modules into partial views that you can include on more then one view.
You can further seperate things into a ViewModel, but then you are going outside of "strict" MVC. In this case, you would use the ViewModel to help the view interact with the model - basically the ViewModel is a modular controller. In this case, the controller would do much less then what little it does already.
However, this is generally overkill for web applications. Because web apps have a single flow of execution (the request) separating things into a ViewModel becomes unnecessary. However, in GUI code, the ViewModel becomes much more useful (as GUIs have much more then a single flow of execution).
You always want to separate business logic into the Model, period. Remember that you should not couple your controller to your model - so that you can use your model elsewhere in other controllers or even expose it as a web service.
Hope this helps
:)
You can do it a couple of ways, but I'd say the easiest way would be to pass in the reference identifier for the user which you are trying to access through to the controller action (as below) and let it do all the data access calls.
public void GetUserAndDetails(Guid userId) { ... }
Then in this controller action you can look up the user details and the books for this user, set the properties on the view model instance and return it to the view to access.
FormViewModel model = new FormViewModel();
model.MyUser = GetUser(userId);
model.UserBooks = GetUserBooks(userId);
return View(model);
This way the view remains dumb (which it should be) and the model is relatively simple. This also helps with testing purposes.
Hope this helps.
In general, this kind of work should be done in the model. This is for a couple of reasons. First, if getting the user books requires a database connection, you don't want to be doing that from the view - it will just slow it down. The other thing to remember is that there could be multiple views, and you would need to duplicate that code in all of the views (web clients, maybe rich clients, etc).
In the MVC pattern, the views should be the "dumb" pieces. This allows easier use of multiple views and changing views when needed. It's also easier to test code when it doesn't require a view, so you could test the model without bringing up a web client.
Jeff
it is the view that is "dumb". all it does is display the manipulated data.
the controller simply fetches data from the model for the view... again the controller is ONLY a go between.
the model does everything. it stores the data and contains the classes and methods that manipulate it.
When you have a viewmodel that is different from your domain model, you shouldn't map the domain model to the viewmodel inside the viewmodel. It would make the viewmodel class responsible for more than one thing. You can do the mapping in the controller or in a service layer.
Check out this. You are talking about VIEW model, not domain model. There is a huge difference. View model should be dumb, it's just a placeholder for data which allows your views to be more strongly typed. Domain model must be a heart of your app, it must contain ALL business logic.
MVC is a pattern by itself. I really don't have any experience with ASP.NET MVC, but worked several times and used MVC pattern. Sometimes, MVC is realted to other development patterns like heartbeat, memento, state ...
No business logic is allowed for a Model! It's a bad design!
Your logic must be in the Controllers and more exactly: place your logic into the Helpers (the Helpers might consume your BLL and/or DAL) and then use your Helpers in your Controllers.
I'm currently in the process of converting some small personal web sites from WebForms to MVC. With the existing sites, the database schema is solid but I had never really taken the time to build proper data/business models/layers. The aspx pages all talked to the database directly using a variety of Views and Stored Procedures that were created as needed for convenience. With MVC, I'm now trying to "do it right" as they say and use things like LINQ to SQL and/or the Entity Framework to build a proper data model or models for the application.
My question revolves around what goals I should have for building data models. I've read various pattern related articles and I realize that ultimately the answer is likely going to depend on the characteristics of my data. But generally should I attempt to build bigger models that encompass as much of the database as possible so that there's only one way to interact with a given set of tables? Or should I build smaller custom models for each MVC View that only contain the data and access that View will need?
Or should I build smaller custom models for each MVC View that only contain the data and access that View will need?
This would probably be better.
Do not forget, you can stick your models in hierarchies, so common properties, like ids, names, preferences can be present in each model.
Fat expanded models could be better for enterprise application, where framework automatically does lot of stuff based on preloaded user preferences, user roles, access rights etc. For a small personal project would probably be better to try to keep your models small and clean. It is also a protection. By not putting unnecessary data into a model you ensure your view will not by mistake display wrong entries or submitting a form would not by mistake overwrite some other data.
I would go for the model representing the actual data logic within your current system and have your controllers return the piece of the model which the view needs such as:
Controller:
public ActionResult index()
{
var ListOfObjects = DataHelper.GetAll();
ViewData.Add(ListOfObjects);
return View();
}
public ActionResult ViewObject(int id)
{
var Object= DataHelper.GetObject();
ViewData.Add(Object);
return View();
}
public ActionResult ViewObjectChild(int Objectid, int ChildId)
{
var Child= DataHelper.GetChildObject(Objectid, ChildId);
ViewData.Add(Child);
return View();
}
On the view
/
<% var myListOfObjects = ViewData.Get<IList<Object>>(); %>
/ViewObject/1/
<% var myobject= ViewData.Get<Object>(); %>
/ViewChild/1/1/
<% var myChild = ViewData.Get<Child>(); %>
Note I have used MVC Contrib typed functions I highly recommend these.
Generally, you would have one comprehensive domain model for the database. You can use (modify/add/remove/etc.) the domain model in your service layer or the controller if it is a small app.
However, for your views, you can use presentation objects to make the views easier to maintain. These are sometimes also called DTO or view model objects. Basically what you do is create an object that contains all the data from the model that is necessary for the view to be populated.
For example:
Your model may include:
public class Car()
{
public string Model;
}
public class Driver()
{
public string Name;
}
You want the view to output the name and model of the car and you would have to pass both the Car and Driver model objects the view.
Rather than sending the two model objects directly from the controller to the view, you can create an object which contains just the data you need:
public class CarAndDriverViewModel()
{
public string CarMake;
public string DriverName;
}
You would populate this object from the domain data and pass that to the view. And the view would be:
model.DriverName + ": " + model.CarMake
Now you don't have to worry about lazy loading issues or complicated view logic to deal with model peculiarities. It's more work to create these view model objects but they really help keep the view clean and provides an easy way to do formatting before sending data to the view.
There are projects and conventions you can use to help automate the creation of the view models, if you want to look into them. AutoMapper is an example.