My question here is if I should place a RowVersion [TimeStamp] property in every entity in my domain model. For Example: I have an Order class and an OrderDetails "navigation, reference" property, should I use a RowVersion property for both entities, or is it enough to the parent object?
These classes are pocos meant to be used with Entity Framework Code First approach.
Thank you.
The answer, as often, is "it depends".
Since it will almost always be possible to have an Order without any OrderDetails, you're right that the parent object should have a RowVersion property.
Is it possible to modify an OrderDetail without also modifying the Order? Should it be?
If it isn't possible and shouldn't be, a RowVersion property at the detail level doesn't add anything. You already catch all possible modifications by checking the Order's RowVersion. In that case, only add the property at the top level, and stop reading here.
Otherwise, if two independent contexts load the same order and details, both modify a different OrderDetail, and both try to save, do you want to treat this as a conflict? In some cases, this makes sense. In other cases, it doesn't. To treat it as a conflict, the simplest solution is to actually mark the Order as modified too if it is unchanged (using ObjectStateEntry.SetModified, not ObjectStateEntry.ChangeState). EF will check and cause an update to the Order's RowVersion property, and complain if anyone else made any modifications.
If you do want to allow two independent contexts to modify two different OrderDetails of the same Order, yes, you need a RowVersion attribute at the detail level.
That said: if you load an Order and its OrderDetails into the same context, modify an OrderDetail, and save your changes, Entity Framework may also check and update the Order's RowVersion, even if you don't actually change the Order, causing bogus concurrency exceptions. This has been labelled a bug, and a hotfix is available, or you can install .NET Framework 4.5 (currently available in release candidate form), which fixes it even if your application uses .NET 4.0.
