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
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
In an ASP.NET MVC project we are using AutoMapper to map from domain model to viewmodel - and sometimes also flattening a hierarchy while doing so. This works like a charm and makes the rendering logic of our views very lean and simple.
The confusion starts when we want to go the other way from viewmodel (or postmodel or editmodel) to domain model, especially when updating objects. We can't use automated/two-way mapping because:
we would have to unflat the flattened hierarchy
all properties on the domain model would have to be mutable/have public setters
the changes coming from the view isn't always just flat properties being mapped back to the domain, but sometimes need to call methods like "ChangeManagerForEmployee()" or similar.
This is also described in Jimmy Bogards article: The case for two-way
mapping in AutoMapper, but the solution to this isn't described in detail, only that they go:
From EditModel to CommandMessages – going from the loosely-typed
EditModel to strongly-typed, broken out messages. A single EditModel
might generate a half-dozen messages.
In a similar SO question there is an answer by Mark Seeman where he mentions that
We use abstract mappers and services to map a PostModel to a Domain Object
but the details - the conceptual and technical implementation - is left out.
Our idea right now is to:
Recieve a FormCollection in the controller's action method
Get the original domain model and flatten it to viewModelOriginal and viewModelUpdated
Merging the FormCollection into viewModelUpdated using UpdateModel()
Use some generic helper method to compare viewModelOriginal with viewModelUpdated
Either A) Generate CommandMessages a la Jimmy Bogard or B) Mutate the differences directly into the domain model through properties and methods (maybe mapping the 1-1 properties directly through AutoMapper)
Can someone provide some examples of how they come from FormCollection through editmodel/postmodel to domain model? "CommandMessages" or "abstract mappers and services"?
I use the following pattern:
[HttpPost]
public ActionResult Update(UpdateProductViewModel viewModel)
{
// fetch the domain model that we want to update
Product product = repository.Get(viewModel.Id);
// Use AutoMapper to update only the properties of this domain model
// that are also part of the view model and leave the other properties unchanged
AutoMapper.Map<UpdateProductViewModel, Product>(viewModel, product);
// Pass the domain model with updated properties to the DAL
repository.Update(product);
return RedirectToAction("Success");
}
You might want to consider CQRS(Command Query Responsibility Segregation - I think this might be the concept you were missing), possibly even with Event Sourcing.
It is basically a practice of separating the logic of reading from a data source and writing to a data source, might even mean having different data models for reading and writing.
This might be a good place to start: http://abdullin.com/cqrs/
Option C: Put it all in the controller action. Next, if that gets hairy, decompose into services (abstract mappers) or messages-as-methods (the command message way).
Command message way:
public ActionResult Save(FooSaveModel model) {
MessageBroker.Process(model);
return RedirectToAction("List");
}
And the processor:
public class FooSaveModelProcessor : IMessageHandler<FooSaveModel> {
public void Process(FooSaveModel message) {
// Message handling logic here
}
}
This is really just about moving the "processing" of the form out of the controller action and into individual, specialized handlers.
But, I'd only really go this route if controller actions get hairy. Otherwise, just take the form and do the appropriate updates against the domain models as necessary.
There are some similarities here with what I've been doing. My hierarchy of view models is only somewhat flattened from its domain object equivalents, but I do have to deal with calling explicit service methods on save to do things like adding to child collections, changing important values etc, rather than simply reverse mapping. I also have to compare before and after snapshots.
My save is Ajax posted as JSON to an MVC action and enters that action magically bound back to a view model structure by MVC. I then use AutoMapper to transform the top level view model and its descendants back into its equivalent domain structure. I have defined a number of custom AutoMapper ITypeConverters for those cases where a new child item has been added on the client (I'm using Knockout.js) and I need to call an explicit service method. Something like:
foreach (ChildViewModel childVM in viewModel.Children)
{
ChildDomainObject childDO = domainObject.Children.Where(cdo => cdo.ID.Equals(childVM.ID))).SingleOrDefault();
if (childDO != null)
{
Mapper.Map<ChildViewModel, ChildDomainObject>(childVM, childDO);
}
else
{
MyService.CreateChildDO(someData, domainObject); // Supplying parent
}
}
I do a similar thing for deletes and this process cascades quite nicely down through the whole structure. I guess a flattened structure could be either easier to work with or harder - I have an AbstractDomainViewModel with an ID with which I do the above matching, which helps.
I need to do comparisons before and after updating because my service layer calls trigger validation which can affect other parts of the object graph, and this dictates what JSON I need to return as the Ajax response. I only care about changes which are relevant to the UI, so I transform the saved domain object back to a new view model and then have a helper method to compare the 2 view models, using a combination of manual upfront checks and reflection.
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,.
I'm begginer in asp.net mvc and i have some doubts.
P.S: I'm using DDD to learn
I have an ACtion in a Controller and it'll save an entity (from my model) by a repository (for a database).
My doubts is, How can I get the informations from the View and save it by a repository in my Controller ?
Is it correct to get an entity of my Model in Save method of controller, like this:
public ActionResult Save(Product product)
{
// validate object
// save data in repository
return View("Success");
}
Or Need I get an DTO (with a structure similar to my entity) and create an object passing property by property to an entity ?
I didnt' like of FormCollection and I'd like to know, What is recommended architecturally ?
Thanks a lot guys
Cheers
I you want to follow DDD practices as described by the Blue Book you should bind your views to DTO's which can be forwarded to a thin 'Application' layer where Domain objects are created or retrieved from database. This application layer can be a simple facade with methods or can leverage command pattern.
For a live demo, you can see my project -- DDDSample.NET
This kind of problem can be fixed by adding so called view model.
Basically - a view model is DTO that provides data for particular view. In similar fashion - view models are used to get data back from view via model binding. Then - controller just forwards necessary data to domain model.
Typically, in ASP.NET MVC your controller actions will receive strongly typed objects returned by the DefaultModelBinder when editing entity types. Using this pattern you can pass a "Product" to your GET view either by itself or as part of a DTO and then your "Save" method would receive a "Product" object in its parameter list.
So long as you are using either editor templates or fields with matching names (i.e. Html.TextBox("Name") corresponds to Product.Name) then the DefaultModelBinder should be able to correctly fill the typed entity object passed to the action method. You shouldn't have to mess with the FormCollection except in certain edge cases.
[HttpGet]
public ActionResult Create() {
return View("Create", new Product());
}
[HttpPost]
public ActionResult Create(Product product) { //or Save(Product)
...
}
As long as your form has fields which match the fields in Product, they should automatically be populated for you based on the values. How you save the entity depends on the data model, whether you're creating a new record or editing an existing one, etc.
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.