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    <p>To me it sounds like you are thinking about it the wrong way round. When you ask "How to create and manage the ViewModels for the Models which implement DB tables with many to many relationships" it sounds like you are thinking about ViewModels in terms of Models. Which isn't right. A ViewModel is a model of a View - not the Model. You shouldn't be thinking about creating ViewModels for your models, you should be thinking about creating VewModels of your Views. </p> <p>In fact the model doesn't even come into it until the end. Start with your UI - your View. You then create a logical representation of that View in code so that you can bind to it, your ViewModel. Then finally you implement your ViewModel by accessing your Model to do what ever needs to be done. When you come to design the next View, even though it might contain some of the same data as the first, you would still create a new model for it - another ViewModel. Now the new ViewModel could include some of the same properties at the first ViewModel, which is fine. Remember is is a model of the View not the Model.</p> <p>Consider an email app, with 2 views, summary and detail. Because there are 2 different Views you have 2 different ViewModels even though the are both pulling data from the same underlying model.</p> <pre><code>Model SummaryViewModel DetailsViewModel ----- --------------- ---------------- RecipientAddress RecipientAddress SenderAddress SenderAddress SenderAddress Subject Subject Subject Content Content </code></pre> <p>Now the Summary View is only a summary and doesn't display the RecipientAddress or the Content so consequently those properties don't exist on the SummaryViewModel. The Details View displays more information, so has more properties. This same idea answers your question about foreign keys. Foreign keys are never visible on your View therefore have no business being members of your ViewModel. Your ViewModel cares only about what is required for the View.</p> <p>In answer to your question "how do you manage the view models": you don't. You don't have to. ViewModel instances usually (not not always) have a one to one relationship with the Views, therefore you don't need to manage them. They only live as long as the view lives. You just create a new instance of the ViewModel when the View is loaded (typically in OnNavigatedTo event handler, see below) and store it in the View's DataContext. If two instances of the View are loaded, then there are two ViewModels. When the View is GC'ed, the ViewModel is too (if it isn't you have a memory leak).</p> <p>Finally, as for how you should synchronize changes, that can be tricky in a desktop Silverlight app where many views might display concurrently. Fortunately on the Windows Phone we usually only have one view open at a time (although not always). So we can simply tell our ViewModel to refresh each time the page is navigated to:</p> <pre><code>protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e) { base.OnNavigatedTo(e); if (DataContext == null) DataContent = new MyViewModel(); //Create new instance of the ViewModel else (MyViewModel)DataContext.Refresh(); //Refresh the existing ViewModel } </code></pre> <p>This works well in most cases for more advanced scenarios you could look at the messaging infrasructure provided by a toolkit like Prism or MvvmLight.</p> <p>Hope this has helped.</p>
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    1. POHow to create the ViewModel(s) for many Views sharing the same Model?
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    1. POHow to create the ViewModel(s) for many Views sharing the same Model?
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    1. COI read you perfectly with regard to View - ViewModel relationship. What I am interested in is the ViewModel - Model relationship: "Then finally you implement your ViewModel by accessing your Model to do what ever needs to be done." - what things to consider here, how is the model shared between different views, including those which will modify the data. For the time being, I am not considering using any of the mentioned toolkits.
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    2. COThats good, you don't need toolkits to do MVVM. There are many ways to share the model between different VM. You might, for example follow a type repository pattern (http://msdn.microsoft.com/en-us/library/ff649690.aspx). Depending on your scenario you you might just new up model objects in your ViewModels. I often create classes services in my application which handle creating and caching of the models (not unlike the repository pattern), which can be requested as required by the ViewModels.
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    3. COI got the idea, in general, but let's take this concrete example, based on the object model presented earlier.
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Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

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