WPF, WCF, Entity, MVVM doubts!

I am using a WCF service reference in a WPF project, and my entity framework data model resides in WCF project.

And I am using MVVM Light framework. I am doing the following things:

1. I use LINQ in the service to get data and then fetch it from WPF, obersvablecollec开发者_如何学编程tions usually.
2. Everything works in view part like populating datagrid, views as required.

But I have following doubts:

1. Is this correct way of transferring data between wcf and wpf.
2. I haven't used the Model for anything yet, I have doubt about when to use it?
3. I also wanted to save data from datagrid. I was able to pass on the observablecollection of updated data of datagrid to the service's function. But how do i update the entity from this collection? by looping? doesnt sound right. Once I update the entity from this collection I will be able to use saveChanges to update into database.
4. When I need to show hierarchal data in a treeview, where to make that data hierarichal, from stored procedure xml? use a view to create a grouping criteria column? create this column in service? create this column/property in presentation?

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1 - There is no correct way, it depends on your requirements and goals.

2 - With MVVM, the model should sit between WPF and the database. That means all calls to the database should go through the model, and all writes to the database should also go through the model. The WPF GUI should only bind to the model. This usually means that your WPF portion consists mostly of XAML code. All code that accesses the database should be in the model.

There are good reasons for separating this.

• You can write unit tests that on the model.
• The view model is independent from the look of the GUI. This means that you can easily change the GUI by dropping in different components and just binding to the model.
• A quick google search can probably yield more reasons.

3 - I would try to send over only the entities that have changed. This can be done by passing the collection to your view model, and have your view model figure out what has changed.

4 - I don't quite understand what you want to do. Usually, to make a TreeView, you should create HierarchicalDataTemplate for each of your view models. The TreeView control will take care of the rest. You should really do some tutorials on this one, because it's kinda hard to wrap your head around.