c# - How to refresh an Entity Framework Core DBContext?

Question

When my table is updated by another party, the db context in dotnet core still return the old value, how can I force the Db context to refresh?

I've done research but I only found people use Reload method, which is not available in EF core, to force the context to refresh.

Some other solution suggests dispose the context after using, but I get error saying the DB context is created by dependency injection and I should not mess up with it.

Answer 1

Oh, this issue had me in knots for days.

I'm using Visual Studio 2017 with .Net Core 2.1, and my EF Core code looked something like this:

//  1.  Load a [User] record from our database 
int chosenUserID = 12345;
User usr = dbContext.Users.FirstOrDefault(s => s.UserID == chosenUserID);

//  2. Call a web service, which updates that [User] record
HttpClient client = new HttpClient()
await client.PostAsync("http://someUrl", someContent);

//  3. Attempt to load an updated copy of the [User] record
User updatedUser = dbContext.Users.FirstOrDefault(s => s.UserID == chosenUserID);

At step 3, it would simply set "updatedUser" to the original version of the [User] record, rather than attempting to load in a fresh copy. So, if, after step 3, I modified that [User] record, I'd actually lose whatever settings the web service had applied to it.

I - eventually - found two solutions.

I could change the ChangeTracker settings. This worked, but I was concerned about the side-effects of doing this:

dbContext.ChangeTracker.QueryTrackingBehavior = Microsoft.EntityFrameworkCore.QueryTrackingBehavior.NoTracking;

Or, I could slip in the following command, before attempting to reload the [User] record...

await dbContext.Entry(usr).ReloadAsync();

This seems to force .Net Core to reload that [User] record, and life is good again.

I hope this is useful...

Tracking down, and fixing this bug took me days....

There's also an excellent article describing the various ways to get around this caching issue here.