WPF - MVVM - Who is responsible for a new DataProvider Connection?

Question

I know this might be a "style of coding" question but at this point I'm really confused. Currently I'm trying to follow the MVVM pattern (ViewModel, Repository, Controller etc.)

But who should initiate a connection to the source of data? Especially when more than one Controller needs an active connection?

There aren't that many possibilities out there - either every Controller itself opens a new connection, the corresponding ViewModel opens the connection and passes it to the repository which in turn passes it to it's controller - or the connection gets instantiated even earlier (eg StartUp.cs).

I know there is no "perfect" solution but I hope to get some inspiration and maybe a good / best practice.

Update 1

Example Code:

namespace Question {
class ViewModel {

    Person.Person p;
    Department.Department d;

    Person.PersonRepository pR;
    Department.DepartmentRepository dR;

    // Here in the VM both classes (Person and Department) intersect - should I inject an instance of a "IDataProvider" from here into the Repositorys?
    // If so, I'd have to pass it to the repository which has to pass it to it's controller.
 }
}

namespace Question.Person {
class Person {
    // Person Model
}

class PersonRepository {
    // This class does whatever a repository does and delegates database query to it's controller
}

class PersonController {

    // Or should the Controller itself instantiate a new "IDataProvider" ?

    // This class needs a connection to the databse to execute querys
 }
}

namespace Question.Department {

class Department {
    // Department Model
}

class DepartmentRepository {
    // This class does whatever a repository does and delegates database query to it's controller
}

class DepartmentController {
    // This class needs a connection to the databse to execute querys
 }
}

Answer 1

I think you misunderstand MVVM pattern. Read this article:

https://msdn.microsoft.com/en-us/magazine/dd419663.aspx

It should help better understood MVVM.

UPDATE:

Repository open connection. If you use ORM to access the database (EF, NHibernate), they usually used connection pool. If you not use ORM then you can implement pool.

http://martinfowler.com/eaaCatalog/repository.html - this article describes pattern "Repository". He implemented collection-like interface and shall hide a features of data access. Hence within the repository should be created connection.

Answer 2

I think you're confusing MVC with MVVM:

The ViewModel is responsible for retrieving the information from the Model, using repositories which get the data from the database, you don't need a controller here.

 public ViewModel()
    {
       Person.PersonRepository pR;
       Department.DepartmentRepository dR;
     }

Or even better inject a repository interface into your ViewModel to get a clean, decoupled and testable implementation:

public ViewModel(IPersonRepository personRepo, IDepartmentRepository depRepo)
    {
       Person.PersonRepository pR = personRepo;
       Department.DepartmentRepository dR = depRepo;
     }