I have to build a number of small independent applications, that can be copied to an USB device and run from there out of the box. So I was thinking to use WPF, that uses EF code first to connect to a SQL Server CE database.
My question is about what architecture I should use. Although the apps are standalone, I would still like to decouple UI from domain from data, to have a clean separation of layers. But I also don't want to make it too complex.
So, I want to have a UI layer (WPF/MVVM) that uses the underlying domain layer (domain objects with domain logic) and repositories (that use EF code first).
My question is: what pattern should I use to make EF work in this case? Is there somewhere an example that demonstrates how to implement CRUD operations in such scenario? For example, should I create one context and leave it open; or should I implement the unit of work pattern and attach objects to other context if needed?
Or would you do it in a totally different way?
Thanks for the advice!
The EF context should be open for as short time as possible. Preferably use it within a using statement.
private static void ApplyItemUpdates(SalesOrderDetail originalItem,
SalesOrderDetail updatedItem)
{
using (AdventureWorksEntities context =
new AdventureWorksEntities())
{
context.SalesOrderDetails.Attach(updatedItem);
// Check if the ID is 0, if it is the item is new.
// In this case we need to chage the state to Added.
if (updatedItem.SalesOrderDetailID == 0)
{
// Because the ID is generated by the database we do not need to
// set updatedItem.SalesOrderDetailID.
context.ObjectStateManager.ChangeObjectState(updatedItem, System.Data.EntityState.Added);
}
else
{
// If the SalesOrderDetailID is not 0, then the item is not new
// and needs to be updated. Because we already added the
// updated object to the context we need to apply the original values.
// If we attached originalItem to the context
// we would need to apply the current values:
// context.ApplyCurrentValues("SalesOrderDetails", updatedItem);
// Applying current or original values, changes the state
// of the attached object to Modified.
context.ApplyOriginalValues("SalesOrderDetails", originalItem);
}
context.SaveChanges();
}
}
There is a method called Attach, which attachs entities to a context:
private static void AttachRelatedObjects(
ObjectContext currentContext,
SalesOrderHeader detachedOrder,
List<SalesOrderDetail> detachedItems)
{
// Attach the root detachedOrder object to the supplied context.
currentContext.Attach(detachedOrder);
// Attach each detachedItem to the context, and define each relationship
// by attaching the attached SalesOrderDetail object to the EntityCollection on
// the SalesOrderDetail navigation property of the now attached detachedOrder.
foreach (SalesOrderDetail item in detachedItems)
{
currentContext.Attach(item);
detachedOrder.SalesOrderDetails.Attach(item);
}
}