Use one entity from two context instance entity framework-CodePudding

I create instance of context per form and may multi forms use same entity How handle this when save?

CodePudding user response：

The DbContext is part of your "view state", intended to give you access to the database, hold a copy of the data the user is working on in the Change Tracker, and flush changes back to the database.

In a smart client app the natural scope and lifetime for the DbContext is either global or scoped to a UI element that represents a task or use-case. But in either case you have to prevent the DbContext's Change Tracker from growing too large or from holding on to copies of data too long, as even a single form can stay open all day. A possible rule-of-thumb for these apps is to clear the change tracker after every successful SaveChanges(). Other than that, of course you must avoid long-running transactions so the DbContext doesn't hold a DbConnection open for a long time, but you have to do that anyway. The point is that a DbContext with an empty change tracker can be long-lived.

Using a Short-Lived DbContext is possible, but you loose the services of the Change Tracker and .Local ObservableCollection which make data binding really easy. So that's not a silver bullet.

So on to the question at-hand, if you have DbContext-per-form, and you have form-to-form communication of entities which end up getting saved by a different DbContext, you really have no choice but to disconnect the entities from their home DbContext before sending them over.

Or this might indicate that the two forms really should share a View State, and you should create an explicit View State object that includes the DbContext and the entieies and have both share that between forms.

Take a look at the Model-View-ViewModel (MVVM) pattern which introduces a distinction between the View (form) and the ViewModel, the data that models the use case user's interaction with the app. It's a useful pattern and is very widely used in XAML-based smart clients. Also XAML is (still) the future of smart client apps, so it's useful to learn.