Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.
Source Error:
public void Trans_Rollback()
{
trans.Rollback();
con.Close();
}
Looks like you disposed 'trans' or 'con' variable (or both) before calling 'TransRollback()'.
If you're using NHibernate, take a look to the querying part. If you use using statement with any of these variables you need to call your rollback method before statement parenthesis closes, since it means disposing object using were used with.
If that's not your case - provide more information, maybe at least framework you're using for accessing database. And context you calling your rollback method from.
Related
I have a fairly simple axon application that Im trying to apply some generic "catch all" exception handling logic to.
If I have a command that goes into an aggregate that throws some kind of exception e.g.
class UserAggregate {
//...
#CommandHandler()
public void on(CreateUserCommand cmd) {
Validate.notNull(cmd.getEmail(), "Email cannot be null");
//other processing
}
}
Then when I invoke this command from the Rest Controller, then the exception is far away from what I would expect
org.axonframework.commandhandling.CommandExecutionException: Email cannot be null
at org.axonframework.axonserver.connector.ErrorCode.lambda$static$10(ErrorCode.java:88)
at org.axonframework.axonserver.connector.ErrorCode.convert(ErrorCode.java:182)
at org.axonframework.axonserver.connector.command.CommandSerializer.deserialize(CommandSerializer.java:157)
at org.axonframework.axonserver.connector.command.AxonServerCommandBus$1.onNext(AxonServerCommandBus.java:313)
at org.axonframework.axonserver.connector.command.AxonServerCommandBus$1.onNext(AxonServerCommandBus.java:306)
at io.grpc.stub.ClientCalls$StreamObserverToCallListenerAdapter.onMessage(ClientCalls.java:429)
at io.grpc.ForwardingClientCallListener.onMessage(ForwardingClientCallListener.java:33)
at io.grpc.ForwardingClientCallListener.onMessage(ForwardingClientCallListener.java:33)
at io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl$1MessagesAvailable.runInternal(ClientCallImpl.java:596)
at io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl$1MessagesAvailable.runInContext(ClientCallImpl.java:581)
Granted the message is useful, however, this is not always a given. This can be mitigated when implementing an ExceptionHandler like so
#ExceptionHandler
public void handle(Exception exception) {
log.info("Caught Exception - {}", exception.getMessage(), exception);
}
This now gives me a stack trace pinpointing where the issue actually came from, however, this comes at the cost of having to write such an ExceptionHandler everywhere I would like to invoke this command.
Is there a more generic way to log these exceptions without having to impose the ExceptionHandler on every class issueing commands?
I would point you to the code-samples repo, where it shows a way of handling it using a MessageHandlerInterceptor.
Quoting from the repo itself:
One of the most common ways to indicate that a logical error has occurred and that Command handling failed is to throw an exception from a Command handler. However, if the exception is directly serialized there is no guarantee that the command sending side can properly deserialize the exception in question.
That is why by default Axon Framework will wrap any exception thrown inside a Command handler into a CommandExecutionException.
In short, you are going to define a MessageHandlerInterceptor responsible to try-catch the command execution logic. There you would have your centralized way of handling the CommandExecutionException.
Entity Framework's DbEntityValidationException renders a message of
Validation failed for one or more entities. See 'EntityValidationErrors' property for more details.
With a stack pointing to where the error occurred. It would be really, really useful if we could dig into the collection of errors, and write out the property and error message. Is there any way in Elmah where we can customize the output for this exception type only?
ELMAH only logs information about an error from the shared stuff on various exception. If the exception message or stacktrace doesnt contain the 'EntityValidationErrors' details, you need to save those yourself.
You can create a filter in ELMAH, implemented to check the type of the exception. If the type is DbEntityValidationException, you can dismiss that exception and raise a new one, containing a ToString of each item in the EntityValidationErrors property as the error detail.
I have one piece of code that gets run on Application_Start for seeding demo data into my database, but I'm getting an exception saying:
The ObjectContext instance has been disposed and can no longer be used for operations that require a connection
While trying to enumerate one of my entities DB.ENTITY.SELECT(x => x.Id == value);
I've checked my code and I'm not disposing my context before my operation, Below is an outline of my current implementation:
protected void Application_Start()
{
SeedDemoData();
}
public static void SeedDemoData()
{
using(var context = new DBContext())
{
// my code is run here.
}
}
So I was wondering if Application_Start is timing out and forcing my db context to close its connection before it completes.
Note: I know the code because I'm using it on a different place and it is unit tested and over there it works without any issues.
Any ideas of what could be the issue here? or what I'm missing?
After a few hours investigating the issue I found that it is being caused by the data context having pending changes on a different thread. Our current implementation for database upgrades/migrations runs on a parallel thread to our App_Start method so I noticed that the entity I'm trying enumerate is being altered at the same time, even that they are being run on different data contexts EF is noticing that something is wrong while accessing the entity and returning an incorrect error message saying that the datacontext is disposed while the actual exception is that the entity state is modified but not saved.
The actual solution for my issue was to move all the seed data functions to the database upgrades/migrations scripts so that the entities are only modified on one place at the time.
hey , I have a problem with updating a record using a domain service, entity framework and asp.net.
Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.
Source Error:
Line 257: }
Line 258: Me.ObjectContext.OrderStatusHistories.AddObject(_orderStatusHistory)
Line 259: Me.ObjectContext.Orders.AttachAsModified(currentOrder, Me.ChangeSet.GetOriginal(currentOrder))
Line 260: End Sub
Line 261:
The order is commited in the database, does anyone know whats going on here?
Turns out the changeset was null. So in my code added an if changeset is not null, i dont need to run the code if there isnt a changeset.
In our application we have to access session objects in business class. We are using HttpContext.Current.Session to get the session value. In some cases it returns the value but mostly its throwing a null reference exception(Object reference not set to an instance of an object). We have the following code
Try
If HttpContext.Current.Session("Username") IsNot Nothing then
' Statements to be executed
End If
Catch ex As Exception
'Log to db
End Try
Here HttpContext.Current.Session("Username") is mostly throwing an exception "Object reference not set to an instance of an object"
While debugging we found that HttpContext.Current itself is nothing.
Thanks. Any help on this will be appreciated.
If the production machine is IIS, there is an installation of "WebSocket protocol".
If the production machine is nginx, you need to set "proxy_set_header Connection" Upgrade ";".