In an mvc project, could someone explain to me the difference between a model and a view model?
My understanding is that a view model reperesents the data for view eg. cshml, but a model represents the data for a partial view. Would this be correct. I have seen the names used in different situations which confuses me so looking for direction on this.
Models are your domain. For example we might have a customer model. We can use this customer in our domain. We can place orders for this customer. We can update the customers contact details, and so forth.
// Domain object, encapsulates state.
class Customer
{
public void PlaceOrder() {...}
public void UpdateContactDetails() { ... }
}
View Models are a way of presenting the data in an easy way. For example, we might have a customer view model. This would be a simple DTO (Data Transfer Object) which allows us to expose the customer to a view. Often view models are created from models - some form of conversion often takes place.
// DTO - exposes state - no domain logic
class CustomerViewModel
{
public string Name { get; set; }
public int Id { get; set; }
}
The benefit of using a view model rather than using your domain objects in your views is that you don't have to expose the innards of your domain to ease presentation logic. I should add that view models are a way of controlling model binding, e.g. if you expose a database record you probably don't want the whole record to be bindable. Using a view model means only those parameters on the model will be bound. Therefore using view models is important from a security point of view. The alternative here is to use whitelists to control what is used during the model binding process - naturally this is tedious and prone to error.
In terms of ASP.NET MVC - the word model is used somewhat interchangeably. In a "real world" project, your domain is likely complex and will not reside inside a Web App, chances are you'll include some other dependency. Therefore the "models" you'll use will be View Models.
In general, in the ASP.NET world, when people refer to models to refer to 'domain models' which are often a 1-1 mapping between say a database table and a C# class.
When referring to view models, these are convenience classes which aid the passing of data between the view (.cshtml) and controller. The view models should contain data relevant to the view, which may contain aggregation data of the domain model (e.g. a property called 'FullName' which is the combination of 'FirstName' and 'LastName') or things like paging info etc.
Personally I prefer to use view models to present data in simple forms to the view, and I make the controller actions take instances of a view model, construct domain models and act on them, either directly or through a service layer.
I'd say that is general a view model holds the data for a specific view/screen/partial view and a model is rather the object representing the business object or entity.
Please look into the following posting, your question was successfully answered: ASP.NET MVC Model vs ViewModel
Hope this helps
