问题:

Why is this happening when we make a call to the AccountApiController.Register() method?

what is trying to use the context?
what is trying to create the context?
how do we avoid this?
how do we debug this?

"Message":"An error has occurred.",

"ExceptionMessage":"The context cannot be used while the model is being created. This exception may be thrown if the context is used inside the OnModelCreating method or if the same context instance is accessed by multiple threads concurrently. Note that instance members of DbContext and related classes are not guaranteed to be thread safe.",

"ExceptionType":"System.InvalidOperationException",

"StackTrace":"

at System.Web.Http.ApiController.d__1.MoveNext()

--- End of stack trace from previous location where exception was thrown

at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)

at System.Runtime.CompilerServices.TaskAwaiter .HandleNonSuccessAndDebuggerNotification(Task > task)

at System.Web.Http.Dispatcher.HttpControllerDispatcher.d__0.MoveNext()"

回答1:

This error can also occur in case of incorrect connectionString. Check if connectionString is valid (no typo etc.).

回答2:

The problem was that we were NOT using the factory pattern that MS recommends.

You can use Factory implementation to get an instance of UserManager from the OWIN context. ... This is a recommended way of getting an instance of UserManager per request for the application.

As a result, "the same context instance is accessed by multiple threads concurrently," because several requests and thus threads shared a DbContext.

This following is correct. It creates a new instance of MyDbContext for each call to the UserManagerFactory function.

UserManagerFactory  = () => new UserManager(new UserStore(new MyDbContext()));

The following is incorrect. It look similar but does not create a new instance for each call to UserManagerFactory. It is what we were using, ergo our site broke.

var userStore = new UserStore(new MyDbContext());                     var userManager = new UserManager(userStore); UserManagerFactory = () => userManager;

回答3:

Do you override the OnModelCreating method? If so, can you share it or the whole context class?

If not, you should pay attention to the following in the error message

or if the same context instance is accessed by multiple threads concurrently. Note that instance members of DbContext and related classes are not guaranteed to be thread safe.

If that doesn't help, do you use an unchanged Web API project which is created by Visual Studio?

回答4:

If you are getting records from Table/View make sure you have sufficient access on the DB objects.

I had the same problem and i resolved it by executing

sp_change_users_login [ @Action = ] 'action' [ , [ @UserNamePattern = ] 'user' ] [ , [ @LoginName = ] 'login' ] [ , [ @Password = ] 'password' ] [;]   sp_change_users_login 'update_one' 'dbuser' 'dblogin'

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