实体框架POCO长期变更跟踪

Question

I'm using .NET entity framework 4.1 with code-first approach to effectively solve the following problem, here simplified.

• There's a database table with tens of thousands of entries.
• Several users of my program need to be able to
  • View the (entire) table in a GridRow, which implied that the entire Table has to be downloaded.
  • Modify values of any random row, changes are frequent but need not be persisted immediately. It's expected that different users will modify different rows, but this is not always true. Some loss of changes is permitted, as users will most likely update same rows to same values.
  • On occasion add new rows.

Sounds simple enough. My initial approach was to use a long-running DbContext instance. This one DbContext was supposed to track changes to the entities, so that when SaveChanges() is called, most of the legwork is done automatically. However many have pointed out that this is not an optimal solution in the long run , notably here . I'm still not sure if I understand the reasons, and I don't see what a unit-of-work is in my scenario either. The user chooses herself when to persist changes, and let's say that client always wins for simplicity. It's also important to note that objects that have not been touched don't overwrite any data in the database.

Another approach would be to track changes manually or use objects that track changes for me, however I'm not too familiar with such techniques, and I would welcome a nudge in the right direction.

What's the correct way to solve this problem?

I understand that this question is a bit wishy-washy, but think of it as more fundamental. I lack fundamental understanding about how to solve this class of problems. It seems to me that long living DbContext is the right way, but knowledgeable people tell me otherwise, which leads me to confusion and imprecise questions.

EDIT1 Another point of confusion is the existance of Local property on the DbSet<> object. It invites me to use a long running context, as another user has posted here .

Answer 1

Problem with long running context is that it doesn't refresh data - I more discussed problems here . So if your user opens the list and modify data half an hour she doesn't know about changes. But in case of WPF if your business action is:

• Open the list
• Do as many actions as you want
• Trigger saving changes

Then this whole is unit of work and you can use single context instance for that. If you have scenario where last edit wins you should not have problems with this until somebody else deletes record which current user edits. Additionally after saving or cancelling changes you should dispose current context and load data again - this will ensure that you really have fresh data for next unit of work.

Context offers some features to refresh data but it only refreshes data previously loaded (without relations) so for example new unsaved records will be still included.

Perhaps you can also read about MS Sync framework and local data cache.

Answer 2

Sounds to me like your users could have a copy (cached) of the data for an indefinate period of time. The longer the users are using cached data the greater the odds that they could become disconnected from the database connection in DbContext. My guess is EF doesn't handle this well and you probably want to deal with that. (eg occaisionally connected architecture). I would expect implementing that may solve many of your issues.