Using EF Core with WPF and I'd like to revert to initial state when a user press Cancel instead of OK on a dialog, is that possible and how?

Question

I'm using EF Core with WPF and I'd like to revert any changes done on any objects to their initial state when a user press Cancel instead of OK on a dialog, is that possible and how?

I'm using a global singleton DbContext where I load all my data model at the beginning of the application. I do not want to know if I should or should not use a DataContext singleton.

When a user has to do some changes on instances in a database, I present a WPF DialogBox where he/she can choose OK or Cancel. On OK, I just do ctx.SaveChanges(). But for Cancel, how can I revert back every changes? How can I come back to a state where all objects returns to their initial state as when the Dialog was called?

I can Dispose the DataContext (which will flush all changes) and reload everything again, but it takes a lot of time. Is there a better way to achieve the task more efficiently by using changes tracked by the DbContext?

I found a GitHub-dotnet/efcore request: Implement RejectChanges() in DbContext #14594. but it doesn’t seem to have any solution.

I think the proper solution should be close to this answer for EF (not core): DbContext discard changes without disposing. I will try to code it (if possible) but an already properly coded solution, and debugged, would be so great!

Update 2022-05-27

After a few trials and errors (like having a singleton Context), I decided to go with something that would require more work, but that with be more in line with the EF Core philosophy. In my case, I load the full model (almost) in memory with "NoTracking". Then when I want to edit an instance (entity), I do so by copying it and makes modification on the copy. If the user choose to apply modifications, then I open a Context and attach to the entity to edit, apply changes to the original entity (copy changes from the copy), and then Ctx.SaveChanges and then Dispose().

@paulsm4, I already done something similar where there was no EFcore implied. But I,m mostly looking a solution where I can use the inner tracking that already exists into EFCore in order to do the job efficiently, generically et easily. I'm pretty sure, many other users would beneficate such a nice feature (like shown in the Github request). Oops comment dispeared.. — Eric Ouellet, May 06 '22 at 18:48

score 3 · Accepted Answer · edited Jun 30 '22 at 12:28

Q: Is that possible and how?

A: Sure.

The most straightforward way is to only "SaveChanges()" when you're "Done" (when the user clicks OK).
Another approach might be to make copies of the original objects, and perform in-process operations on the copies.
If you're continually updating and saving work-in-progress to the DB (possibly an unwise design), then you can also leverage transactions, and rollback if the user hits Cancel.

Example:

https://learn.microsoft.com/en-us/ef/core/saving/transactions

using var context = new BloggingContext();
using var transaction = context.Database.BeginTransaction();

try
{
    context.Blogs.Add(new Blog { Url = "http://blogs.msdn.com/dotnet" });
    context.SaveChanges();

    context.Blogs.Add(new Blog { Url = "http://blogs.msdn.com/visualstudio" });
    context.SaveChanges();

    var blogs = context.Blogs
        .OrderBy(b => b.Url)
        .ToList();

    // Commit transaction if all commands succeed, transaction will auto-rollback
    // when disposed if either commands fails
    transaction.Commit();
}
catch (Exception)
{
    // TODO: Handle failure
}

What I understand is your solution show the "OK" behavior but I'm looking for the "Cancel" Behavior. Where objects revert to their initial states? — Eric Ouellet, May 06 '22 at 18:50
I'm not sure but using Transation implies a road trip to the database where there is no reason to do so. It should be possible to do the revert task locally using only the DbContext Object Change Tracker. — Eric Ouellet, May 06 '22 at 18:54

score 0 · Answer 2 · answered May 06 '22 at 19:11

0

You can use the ChangeTracker to retrieve all tracked EntityEntries. Each EntityEntry contains both the CurrentValues and the OriginalValues for all properties. Documentation

answered May 06 '22 at 19:11

pjs

363
1
7

Thank you for the information. I will check the documentation and code it. When I'm done, I will either accept your answer or tell you what I found. Thanks! – Eric Ouellet May 06 '22 at 19:14

Using EF Core with WPF and I'd like to revert to initial state when a user press Cancel instead of OK on a dialog, is that possible and how?

2 Answers2