Entity Framework + SQL Server Compact + WPF/WinForms = Sluggish UI?

Question

Entity Framework doesn't allow sharing the same entity between multiple database contexts. Therefore, I have to use only one database context in a GUI application (be it WPF or WinForms), because entities need to interact with each other.

SQL Server Compact doesn't allow sharing the same database connection between multiple threads . If I try creating a connection on one thread and running SQL query on another, my application is likely to crash.

Therefore, I have to create EF database context on one thread and run all queries on that thread . I've used GUI thread for that, because almost all queries are very fast. However, now I have a slow query and want to show an animated progress bar while it's being executed.

But I can't do that, because if I run a query on a different thread, my app crashes with AV. Furthermore, EF seems to complain if I run multiple queries simultaneously , even without SQL CE involved. Moving all queries to a different thread, covering all code with crazy amounts of async/await, callbacks, locks and other threading stuff sounds scary too, as I want to keep the code simple if it's possible.

Question: What is the correct way to work with EF database contexts and SQL Server Compact in a multi-threaded GUI application? Is there any way to offload individual queries to a different thread without making the whole application asynchronous, ie is there a simple way to do it?

Answer 1

SQL Server CE supports multithreading. But its objects like SqlCeConnection or SqlCeTransaction are not thread-safe. Each thread should use a separate connection. An Entity Framework DataContext instance is designed to last for one unit of work (bussiness transaction). The recommendation is a context per a form.

You can either redesign your application and store/transfer data using DTOs . Or you can use Attach/Detach features of Entity Framework ( here or here ). Or combine both.