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How to code/design the Model part in Caliburn.Micro?

I am new to MVVM pattern and Caliburn.Micro. I've read some tutorials on how to get started, but I'm confused about the Model part of MVVM in the context of Caliburn.
I want to create my first MVVM application and I have some design questions:
In tutorials, the Model was presented as simple property in
ViewModel. How should I manage more complex models? Is there any
naming convention? Obviously, there should be some external classes
made for my models, but how should I communicate between my models
and the view?
How should I keep references to many instances of one complex model?
For ex. cumtomers (instances of Customer model class)
Is there a possibility to manipulate one model class in many
ViewModels? How should I store my model reference, so it'll be
visible from different ViewModels?
Where should I put my code for more complex model manupulation/file,
database storage? How should I invoke such code? I'm not asking here
about SQLConnections, but MVVM best practices. :)
Thanks in advance for any help :)
EDIT:-------------------------------------------------------
Thank you for your anwser. I uderstand the topic more clearly, but I'm still confused about some details.
For an example, let's assume this little application. I have a form that allows me to add a new Customer. It has a few fields like Name, Surname etc.
After pressing the button, I invoke the addCustomer command in the ViewModel. I want my program to store the newly created customer inside the database.
My view also has the List control (whatever), which displays my customers as raw strings (like "Name: John, Surname: Doe, Address: ..." I know it's dumb to make it like this, but i need an example of model manipulation (like .toString()))
For this example, I've created a bunch of stuff to illustrate my vision of that process:
fields - it's a set of form fields like Name, Surname etc.
customerSet - it's a set of Customer class to store all created
customers
.addToDatabase(fields) - a method which puts newly created customer
to the database
.getStrings - a method which prepares a set of strings to be
displayed by the list in CustomerView
I think about 2 approaches that would be good for a solution:
First approach. I don't like this one. The only advantage is, that
ViewModel handles all the logic inside application. Sharing model
would be a serious problem here, because saving methods are bound to
the ViewModel class.
Second, MVC like approach. To me it's the most intuitive one. But - I
don't know where should I store CustomersModel object, so few
ViewModels could have access to it.
Which is the better one? Or maybe another approach that is more suitable for MVVM?
Another problem is: Where should I put my method that will load all the Customers from the database, so they could be displayes on the list? In "get method" inside viewmodel, or inside a model class?

In tutorials, the Model was presented as simple property in ViewModel.
How should I manage more complex models? Is there any naming
convention? Obviously, there should be some external classes made for
my models, but how should I communicate between my models and the
view?
Your models should represent whatever it is they need to whether it's a customer, account, etc. The view models job is to handle the interaction between the view and models.
How should I keep references to many instances of one complex model?
For ex. cumtomers (instances of Customer model class)
Generally, you will map complex models to more friendly format for display, you can do it manually or use a tool like AutoMapper.
Is there a possibility to manipulate one model class in many
ViewModels? How should I store my model reference, so it'll be visible
from different ViewModels?
If you're working with a local db you can pass IDs around. If it's a service you could persist the model locally for other view models to work with. You could also inject a singleton, ISharedData, into view models that need to work with shared data.
Where should I put my code for more complex model manupulation/file,
database storage? How should I invoke such code? I'm not asking here
about SQLConnections, but MVVM best practices. :)
Create services for more complex model manipulation / business logic. Inject the services into view models that require them. ICustomerService, IAccountService, etc.
EDIT:-------------------------------------------------------
You're first approach is correct. To your point about sharing the model being a serious problem because saving methods are bound to the view model class. The view model will have a SaveCustomerCommand that is fired when the button is clicked, because of its binding.
The SaveCustomerCommand will persist the CustomerModel, regardless of how the CustomerModel is persisted. So if its a database, the view model might have a reference to a context and issue a _db.Save(CustomerModel). If another view model needs to manipulate a CustomerModel, it will do so by using the context. The view model could also have a reference to a CustomerService that handles the crud for the CustomerModel.
Here's how this might look:
public class AddCustomerViewModel : Screen
{
private readonly ICustomerService _customerService;
public AddCustomerViewModel(ICustomerService customerService)
{
_customerService = customerService;
}
//If button is named x:Name="SaveCustomer" CM will
//bind it by convention to this method
public void SaveCustomer(Customer customer)
{
_customerService.Save(customer);
}
}
public class CustomerListViewModel : Screen
{
private readonly ICustomerService _customerService;
private List<CustomerDisplayModel> _customers;
public CustomerListViewModel(ICustomerService customerService)
{
_customerService = customerService;
}
public List<CustomerDisplayModel> Customers
{
get { return _customers; }
set
{
_customers = value;
NotifyOfPropertyChange();
}
}
//only fires once, unlike OnActivate()
protected override void OnInitialize()
{
var customers = _customerService.LoadAllCustomers();
//could just use the model but this shows how one might map from
//the domain model to a display model, AutoMapper could be used for this
Customers = customers.Select(c => new CustomerDisplayModel(c)).ToList();
}
}
public interface ICustomerService
{
List<Customer> LoadAllCustomers();
void Save(Customer customer);
}
//same as button, Label named x:Name="CustomerName" will bind
// to CustomerName
public class CustomerDisplayModel
{
private readonly Customer _customer;
public CustomerDisplayModel(Customer customer)
{
_customer = customer;
}
public string CustomerName
{
get { return _customer.Name; }
set { _customer.Name = value; }
}
public string Surname
{
get { return _customer.Surname; }
set { _customer.Surname = value; }
}
public string Address
{
get { return _customer.Address; }
set { _customer.Address = value; }
}
}
public class Customer
{
public int Id { get; set; }
public string Name { get; set; }
public string Surname { get; set; }
public string Address { get; set; }
}

Who populates the ViewModel in ASP MVC 5

Whose responsibility is it to populate the values in an ASP MVC 5 architecture (C#, EF), for e.g. if we have PurchaseRecordsViewModel , PurchaseRecords Domain Model , PurchaseController
Does the code to populate data (time, cost etc) go it the viewmodel, right in its very own the viewmodel go in the PurchaseRecordsViewModel ?
Or, does the code go in the Action method of the PurchaseController

View models are typically just dumb collections of properties. Populating a view model typically rests inside of your service layer or, if you don't have one, your action method.
Think of the roles this way.
A domain model is a direct mapping to a database table.
A view model is a collection of properties needed to display a view.
A service layer gets/uses one or more domain models and populates a view model.
A service layer also can take a view model and create/update one or more domain models
A controller action method is the glue between the two. It calls a service layer to get (GET) a view model and passes it to a view. These action methods also take (POST) a view model and pass it to the service layer to do whatever needs to be done to it.
Another question typically asked is why can't I use domain models for a view? You can, but typically you run into things like, needing data from more than one domain model, not needing all the properties that are in the domain model and lastly, you now would have to worry about properties being updated on the domain model that you did not intend.

Expanding upon Tommy's answer, here is some code to go along with his description.
//Controller
public ActionResult Index()
{
List<OrderViewModel>() model = new List<OrderViewModel>();
model = new ServiceClass().GetOrders();
return View(model);
}
//here is your Service Class, this layer transfers the Domain Model into your ViewModel
public List<OrderViewModel> GetOrders()
{
List<OrderDomain> model = new List<OrderDomain>();
model = new DataAccess().GetOrders();
List<OrderViewModel> viewModel = new List<OrderViewModel>();
foreach (var order in model)
{
OrderViewModel vm = new OrderViewModel();
vm.OrderId = order.OrderId;
vm.OrderName = order.OrderName;
viewModel.Add(vm);
}
return viewModel;
}
//some DataAccess class, this class is used for database access
Public List<OrderDomain> GetOrders()
{
List<OrderDomain> model = new List<OrderDomain>();
using (var context = new MyEntities())
{
model = (from x in context.Order
select new OrderDomain
{
OrderId = x.OrderId,
OrderName = x.OrderName
}).ToList();
}
return model;
}
Edit:
This seems to be a mildly popular answer so I would like to mention I no longer follow this pattern. Instead I've been using mediatr and vertical slice architecture.

Ideally, PurchaseRecordViewModel should populate itself by getting PurchaseRecordsDomainModel. It should contain simple mapping of properties, and possibly some formatting of the output you're going to use in your view.
PurchaseRecordsViewModel
public class PurchaseRecordsViewModel
{
public IEnumerable<PurchaseRecordViewModel> PurchaseRecords {get;set;}
}
PurchaseRecordViewModel
public class PurchaseRecordViewModel
{
public DateTime Date {get;set;}
public decimal Cost {get;set;}
// .... some other properties
public PurchaseRecordsViewModel(PurchaseRecordsDomainModel domainModel)
{
Date = domainModel.Date;
Cost = domainModel.Cost;
// .... some other property mappings
}
}
What your action method on PurchaseController should do, is orchestrating the process of getting your PurchaseRecordsDomainModel, creation of PurchaseRecordsViewModel from PurchaseRecordsDomainModel and passing it to the View. Action method itself shouldn't contain any code that deals with connecting and retrieving data from database (in your case querying EF context), or any business logic. You should try to have loosely coupled modules, talking to each other via abstractions, this way you will ensure your application is maintainable, extensible and testable.
Also, try to draw clear separation between various layers of your system. For example, it is not a good idea to have EF entities as Domain Model Entites. You don't want your business logic layer to depend on data access layer, think of it this way, what if at some point of time in the future, you are moving away from EF and using some other ORM or even other technology to store and query data. You don't want to change business logic layer just because you're changing your data access layer. So to go from words to code in your case.
Considering that you already have your view and view model, I would create PurchaseRecordsService class in domain layer(please note depending in your case you might not use Repositories, but some other technique, this example is mainly to illustrate my point)
public class PurchaseRecordsService
{
private readonly IPurchaseRecordsRepository _purchaseRecordsRepository;
public PurchaseRecordsService(IPurchaseRecordsRepository purchaseRecordsRepository)
{
if(purchaseRecordsRepository == null)
{
throw new ArgumentNullException("purchaseRecordsRepository");
}
_purchaseRecordsRepository = purchaseRecordsRepository;
}
public IEnumerable<PurchaseRecordsDomainModel> GetPurchaseRecords()
{
// trivial case, real code can be more complex
return _purchaseRecordsRepository.GetPurchaseRecords();
}
}
Then in your domain layer, you could define IPurchaseRecordsRepository
public interface IPurchaseRecordsRepository
{
IEnumerable<PurchaseRecordsDomainModel > GetPurchaseRecords();
}
The idea is, our PurchaseRecordsService needs a way to communicate with databases, so whoever uses it, must supply implementation of IPurchaseRecordsRepository. Next step is to move to our data access layer and create implementation class of IPurchaseRecordsRepository.
public class EfPurchaseRecordsRepository: IPurchaseRecordsRepository
{
private readonly EfObjectContext _objectContext;
public EfPurchaseRecordsRepository(string connectionString)
{
_objectContext = new EfObjectContext(connectionString);
}
public IEnumerable<PurchaseRecordsDomainModel > GetPurchaseRecords()
{
var purchaseRecords = (from p in _objectContext.PurchaseRecords
....
select p).AsEnumerable();
return purchaseRecords .Select(p => p.ConvertToDomainPurchaseRecord());
}
}
And the last piece - we need to define our Action in PurchaseController
public class PurchaseController: Controller
{
private readonly IPurchaseRecordsRepository _repository;
public PurchaseController(IPurchaseRecordsRepository repository)
{
if(repository == null)
{
throw new ArgumentNullException("repository");
}
_repository = repository;
}
public ActionResult Index()
{
var purchaseRecordsService = new PurchaseRecordsService(_repository);
var purchaseRecordsViewModel = new PurchaseRecordsViewModel();
var purchaseRecords = purchaseRecordsService.GetPurchaseRecords();
foreach(var purchaseRecord in purchaseRecords)
{
var purchaseRecordViewModel = new PurchaseRecordViewModel(purchaseRecord);
purchaseRecordsViewModel.PurchaseRecords.Add(purchaseRecordViewModel);
}
return View(purchaseRecordsViewModel);
}
}
To recap, what we have is loosely coupled code, our Presentation and Data Access Layers don't know about each other, and they depend only on Domain layer. If you need, you can replace MVC front end with WPF for example, move from EF to another technology, your code is testable.

Ideally, your view model should be unaware of your domain model, so I'd say that you put your population logic in your controller, perhaps packed away in some sort of mapping/population utility class.
But remember, when it comes to questions about where to put certain logic, personal preference goes a long way.

When should I write code in the controller vs. model?

Without a doubt I know what the controllers and models are used for. However, I am able to write code that interacts with my db, for example adding users to a table, on either the controller or model. At what times should I write code in the controller vs. in model? Even though both work, what would be a more organized or practical way. Could you please post examples if the answer is ambiguous?Thx

For that, you should add a logic layer or logic classes. The controller should determine wants to do and can do, shuffle them in the right direction (logic layer), then determine what to show the user after the logic. Putting the logic in a separate layer will help keep your controllers lean and promote code reuse.
In the domain core, we only have models with properties. All logic is performed in a different layer, except for things like a property that returns fields concatenated in a format.

Code to access the database should be in service layer instead of keeping in Controller or Model.
Accessing Database Entities from Controller
Here is my answer for the above question, you can also read others answers why you should keep in separate layer.
namespace MyProject.Web.Controllers
{
public class MyController : Controller
{
private readonly IKittenService _kittenService ;
public MyController(IKittenService kittenService)
{
_kittenService = kittenService;
}
public ActionResult Kittens()
{
// var result = _kittenService.GetLatestKittens(10);
// Return something.
}
}
}
namespace MyProject.Domain.Kittens
{
public class Kitten
{
public string Name {get; set; }
public string Url {get; set; }
}
}
namespace MyProject.Services.KittenService
{
public interface IKittenService
{
IEnumerable<Kitten> GetLatestKittens(int fluffinessIndex=10);
}
}
namespace MyProject.Services.KittenService
{
public class KittenService : IKittenService
{
public IEnumerable<Kitten> GetLatestKittens(int fluffinessIndex=10)
{
using(var db = new KittenEntities())
{
return db.Kittens // this explicit query is here
.Where(kitten=>kitten.fluffiness > 10)
.Select(kitten=>new {
Name=kitten.name,
Url=kitten.imageUrl
}).Take(10);
}
}
}
}

ASP.NET MVC and MVC, in general, is a presentation layer pattern; thus your interaction with the database should be in a layer beyond the presentation layer, usually a data-access layer, but it could be a service layer or business layer as well.

What is the best practice for base model in MVC 4 project?

I am starting a new MVC project and it is definetly known that each view required the next items: user language, timezone and few user settings referred to city, country, etc. So, I am going to make some base entity where to put this properties. But some view would be type of PagedList (class from opensource MvcPaging library). And I am not sure how to combine Base model and PagedList in one object?
I thank about interfaces but I read that it is more complex rather then using classes.

sounds like you should look into inheritance:
public class BaseModel
{
public string UserLanguage { get; set; }
...
}
public class SomePageModel : BaseModel
{
public int Id { get; set; }
public PagedList<Whatever> PagedStuff { get; set; }
...
}
In this case SomePageModel inherits all properties of BaseModel. You don't need to use PagedList as a Model. You can use SomePageModel as a model for a view, which has inside the PagedList. In this case you'd write in the view:
#model [namespace].SomePageModel
//to access paged stuff:
#Model.PagedStuff
But really your question lucks specifics and it's hard to direct you in the correct direction based on the information you've provided thus far.

ASP.NET MVC3 - Unmutable model - Add validation attributes

I have a set of model classes from another section of the application that cannot be modified. These do not have the validation attributes I need (RemoteAttribute for instance). How do I go about adding these? I can't add [MetadataTypeAttribute] to models.
To illustrate:
//in Models.dll
//remember: I can't modify this
public class Product
{
string Name { get; set; }
}
//in Web.dll
public class ProductController
{
// GET: /Product/
public ActionResult Index()
{
return View(new Product());
}
}
//what i need:
public class ProductMetadata
{
[Remote("Foo", "Bar")]
[RegularExpression]
string Name { get; set; }
}
Is this in any way possible without creating a ViewModel class or something of that sort?

Is this in any way possible without creating a ViewModel class
Assuming that a properly architected ASP.NET MVC application should always use view models you can only benefit from introducing them. In addition to solving this particular problem and hundreds of potential other problems you will have a properly architected ASP.NET MVC application :-)
Tying your model to a controller (which is what the RemoteAttribute will do) seems like a horrible idea in terms of reusability of this model in other applications.